Shape coexistence in Hg-178

Lifetime measurements of excited states in Hg-178 have been performed using the Rh-103(Kr-78, p2n) reaction at a beam energy of 354 MeV. The recoil-decay tagging (RDT) technique was applied to select the Hg-178 nuclei and associate the prompt gamma rays with the correlated characteristic ground-state alpha decay. Lifetimes of the four lowest yrast states of Hg-178 have been determined using the recoil distance Doppler-shift (RDDS) method. The experimental data are compared to theoretical predictions with focus on shape coexistence. The results confirm the shift of the deformed prolate structures to higher lying states but also indicate their increasing deformation with decreasing neutron nu…

A Geant4 simulation package for the sage spectrometer

International audience; A comprehensive Geant4 simulation was built for the SAGE spectrometer. The simulation package includes the silicon and germanium detectors, the mechanical structure and the electromagnetic fields present in SAGE. This simulation can be used for making predictions through simulating experiments and for comparing simulated and experimental data to better understand the underlying physics.

Investigation of the Δn = 0 selection rule in Gamow-Teller transitions : The β-decay of 207Hg

Gamow-Teller β decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This Δn = 0 requirement plays a major role in the β decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical r-process pathway below both Z = 50 (for N > 82) and Z = 82 (for N >126). The level of forbiddenness of the Δn = 1ν1g9/2 → π0g7/2 transition has been investigated from the β− decay of the ground state of 207Hg into the single-proton-hole nucleus 207Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible γ-ray transitions depopulating the π0…

Alpha-decay studies of the francium isotopes 198Fr and 199Fr nuclei

Very neutron deficient francium isotopes have been produced in fusion evaporation reactions using 60Ni ions on 141Pr targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two α-particle activities, with Eα = 7613(15) keV and T1/2 = (15+12 −5 ) ms and Eα = 7684(15) keV and T1/2 = (16+13 −5 ) ms were identified in the new isotope 198Fr. In addition, the half-life and α-particle energy of 199Fr wer…

In-beam spectroscopic study of Cf244

The ground-state rotational band of the neutron-deficient californium (Z = 98) isotope 244Cf was identified for the first time and measured up to a tentative spin and parity of I I-pi = 20(+). The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured gamma-ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high-j orbitals starting at a rotational frequency of about (h) over bar (omega) = 0.20 MeV. The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with avail…

Towards saturation of the electron-capture delayed fission probability : The new isotopes 240Es and 236Bk

The new neutron-deficient nuclei 240Es and 236Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240Es produced in the fusion–evaporation reaction 209Bi(34S,3n)240Es. Half-lives of 6(2) sand 22+13−6swere obtained for 240Es and 236Bk, respectively. Two groups of αparticles with energies Eα=8.19(3) MeVand 8.09(3) MeVwere unambiguously assigned to 240Es. Electron-capture delayed fission branches with probabilities of 0.16(6)and 0.04(2)were measured for 240Es and 236Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes. peerReviewed

Isomeric state in the doubly odd196At nucleus

An excited isomeric state has been identified in the 196At nucleus using the recoil decay tagging technique. This is the first identification of an excited state in this neutron-deficient odd-odd nucleus. Several tentative prompt γ-rays have also been correlated with 196At α-decay, although it has not been possible to assign them to specific energy levels in 196At. The mean lifetime of the isomeric state has been measured as τ = 11±2 µs. The new level is compared with similar low-lying states in neighbouring nuclei and is de-excited by an E2 γ-ray transition, the large hindrance of which is not expected.

Recoil isomer tagging in the proton-rich odd-odd N = 77 isotones, 142Tb and 144Ho

A fusion-evaporation reaction has been employed to search for isomeric states in the near-proton drip-line N577 isotones, 65 142Tb and 67 144Ho. The recoiling nuclei were implanted into a silicon detector at the focal plane of a gas-filled separator, where a recoil isomer tagging technique was employed to correlate prompt and delayed g-ray transitions across isomeric states. New states were observed to be built upon a known 15-ms isomer in 142Tb and the feeding and decay of a new 500(20)-ns isomeric state was established in 144Ho. This measurement represents the first observation of excited states in 144Ho. The behavior of the new states above the isomers suggests that they are built upon l…

The SAGE spectrometer: A tool for combined in-beam gamma-ray and conversion electron spectroscopy

International audience; The sage spectrometer allows simultaneous in-beam -ray and internal conversion electron measurements, by combining a germanium detector array with a highly segmented silicon detector and an electron transport system. sage is coupled with the ritu gas- lled recoil separator and the great focal-plane spectrometer for recoil-decay tagging studies. Digital electronics are used both for the ray and the electron parts of the spectrometer. sage was commissioned in the Accelerator Laboratory of the University of Jyvaskyla in the beginning of 2010.

High-spin spectroscopy of 140Nd

The population of the high-spin states in 140Nd was investigated using the reaction 96Zr(48Ca,4n). The results from two experiments, one with the EUROBALL array and one with the JUROGAM II + RITU + GREAT setup employing the recoil decay tagging technique, have been combined to develop a very detailed level scheme for 140Nd. Twelve bands of quadrupole transitions and eleven bands of dipole transitions were identified and their connections to low-lying states were established. Calculations using the cranked Nilsson-Strutinsky and the tilted axis cranking models were used to interpret the observed structures. The overall good agreement between the experimental results and the calculations assu…

Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes

Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient Po196,198,200,202 isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, Po200,202, the transitional and diagonal matrix elements of the 2+1 state are determined. In Po196,198 multistep Coulomb excitation is observed, populating the 4+1,0+2, and 2+2 states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from Po196 onwards. Three model descriptions are used to compare to the data. Calculati…

The GREAT spectrometer

Abstract The GREAT spectrometer is designed to measure the decay properties of reaction products transported to the focal plane of a recoil separator. GREAT comprises a system of silicon, germanium and gas detectors optimised for detecting the arrival of the reaction products and correlating with any subsequent radioactive decay involving the emission of protons, α particles, β particles, γ rays, X-rays or conversion electrons. GREAT can either be employed as a sensitive stand-alone device for decay measurements at the focal plane, or used to provide a selective tag for prompt conversion electrons or γ rays measured with arrays of detectors deployed at the target position. A new concept of …

Lifetime Measurements of Excited States in Pt172 and the Variation of Quadrupole Transition Strength with Angular Momentum

Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1…

Electromagnetic transition strengths in 109Te

Lifetime measurements have been made in the neutron-deficient nucleus 109Te using the coincident recoil distance Doppler-shift method. The experimental B(E2) values have been compared with state-of-the-art shellmodel calculations using the monopole-corrected realistic charge-dependent Bonn nucleon-nucleon potential. Lifetimes in the νh11/2 band are consistent with an interpretation based on the deformation driving properties of a single valence neutron outside of the even-even tellurium core and highlight the unexpected presence of collective behavior as the N = 50 shell closure is approached. Lifetime measurements for the low-lying positive-parity states also appear to correlate well with …

Collective excitations in the transitional nucleiRe163andRe165

Excited states in the neutron-deficient nuclei ${}_{75}^{163}{\mathrm{Re}}_{88}$ and ${}_{75}^{165}{\mathrm{Re}}_{90}$ were populated in the ${}^{106}{\mathrm{Cd}(}^{60}\mathrm{Ni},\phantom{\rule{0.16em}{0ex}}p2n\ensuremath{\gamma})$ and ${}^{92}{\mathrm{Mo}(}^{78}\mathrm{Kr}$, $3p2n\ensuremath{\gamma})$ fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. \ensuremath{\gamma} rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for $^{163}\mathrm{Re}$ and $^{165}\mathrm{Re}$ were identifie…

Spectroscopy of the proton drip-line nucleus 203Fr

The nucleus ${}^{203}$Fr has been studied through $\ensuremath{\gamma}$-ray and electron spectroscopy, using the recoil-decay tagging technique. A 13/2${}^{+}$ state, with a half-life of 0.37(5) $\ensuremath{\mu}$s, has been observed in ${}^{203}$Fr. Both the $\ensuremath{\alpha}$-decay branch and the internal de-excitation of the 1/2${}^{+}$ isomer in ${}^{203}$Fr have been studied. Furthermore, the corresponding 1/2${}^{+}$ state, with a half-life of 0.31(8) s, has been found in ${}^{199}$At. In addition, transitions feeding the 9/2${}^{\ensuremath{-}}$ ground state of ${}^{203}$Fr have been identified. The observed level pattern suggests that the ground state is still spherical.

Prompt and delayed spectroscopy of 203At : Observation of a shears band and a 29/2+ isomeric state

Using fusion-evaporation reactions, a gas-filled recoil separator, recoil-gating technique and recoil-isomer decay tagging technique we have extended the level scheme of 203 At ( N = 118 ) significantly. We have observed an isomeric [ τ = 14.1 ( 3 ) μ s ] state with a spin and parity of 29 / 2 + . The isomeric state is suggested to originate from the π ( h 9 / 2 ) ⊗ ∣ ∣ 202 Po ; 11 − ⟩ coupling, and it is depopulated through 286 keV E 2 and 366 keV E 3 transitions. In addition, we have observed a cascade of magnetic-dipole transitions which is suggested to be generated by the shears mechanism. peerReviewed

Development of a new Recoil Distance Technique using Coulomb Excitation in Inverse Kinematics

We report on an experiment using Coulomb excitation in inverse kinematics in combination with the plunger technique for measuring lifetimes of excited states of the projectiles. Aside from the investigation of E(5) features in 128Xe, the aim was to explore the special features of such experiments which are also suited to be used with radioactive beams. The measurement was performed at the JYFL with the Koln coincidence plunger device and the JUROGAM spectrometer using a 128Xe beam impinging on a natFe target at a beam energy of 525 MeV. Recoils were detected by means of 32 solar cells placed at extreme forward angles. Particle‐gated γ‐singles and γγ‐coincidences were measured at different t…

Confirmation of the new isotope Pb178

The extremely neutron-deficient isotope $^{178}\mathrm{Pb}$ has been produced. The GREAT spectrometer at the focal plane position of the gas-filled separator RITU was used to study the $\ensuremath{\alpha}$ decay of $^{178}\mathrm{Pb}$ and its $\ensuremath{\alpha}$-decay chain through $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}$ correlations. The $\ensuremath{\alpha}$ decay was measured to have an energy and half-life of ${E}_{\ensuremath{\alpha}}$= 7610(30) keV and ${t}_{1/2}=0.{21}_{\ensuremath{-}0.08}^{+0.21}$ ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and proximity potential model. The $\ensuremath{\alpha}$-decay…

Collective rotational – vibrational transition in the very neutron-deficient nuclei Pt

Excited states have been identified for the first time in very neutron deficient Pt-171.172 nuclei using the recoil-or-decay tagging technique. The ground-state band in Pt-172 has been established up to I-pi = 8+. A similar level sequence, presumably built on the I-pi = 13/2(+) state, is observed for Pt-171. The data are compared with theoretical calculations based on the mean field approach and the random phase approximation and are put into the context of the systematics of platinum isotopes. (C) 1998 Elsevier Science B.V. All rights reserved.

First observation of excited states of173Hg

The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of gamma rays decaying from excited states are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighbouring neutron-deficient Hg nuclei. In addition to the gamma-ray spectroscopy, the alpha decay of this nucleus has been measured yielding superior precision to earlier measurements.

α -decay spectroscopy of the N=130 isotones Ra218 and Th220 : Mitigation of α -particle energy summing with implanted nuclei

© 2019 American Physical Society. An analysis technique has been developed in order to mitigate energy summing due to sequential short-lived α decays from nuclei implanted into a silicon detector. Using this technique, α-decay spectroscopy of the N=130 isotones Ra218 (Z=88) and Th220 (Z=90) has been performed. The energies of the α particles emitted in the Ra218→Rn214 and Th220→Ra216 ground-state-to-ground-state decays have been measured to be 8381(4) keV and 8818(13) keV, respectively. The half-lives of the ground states of Ra218 and Th220 have been measured to be 25.99(10) μs and 10.4(4) μs, respectively. The half-lives of the ground states of the α-decay daughters, Rn214 and Ra216, have …

Prompt gamma ray-spectroscopy of N = 50 fission fragments

Excited states in the nuclei 83 As and 84,86 Se have been studied via prompt -ray spectroscopy. The nuclei were produced by the proton-induced fission of a 238 U target, at the accelerator of the University of Jyvaskyla. The JUROGAM-II array was used to detect prompt -rays and a triple- coincidence analysis performed. A comparison of the N = 50 nuclei with shell-model calculations reproduces the low-lying states in 83 As and 84 Se well. The inclusion of particle-hole excitations is necessary to correctly describe the states above ∼ 3.5 MeV.

The JUROGAM 3 spectrometer

AbstractThe jurogam 3 spectrometer has been constructed for in-beam $$\gamma $$γ-ray spectroscopy experiments in the Accelerator Laboratory of the University of Jyväskylä, Finland. jurogam 3 consists of germanium-detector modules in a compact geometry surrounding a target to measure $$\gamma $$γ rays emitted from radioactive nuclei. jurogam 3 can be employed in conjunction with one of two recoil separators, the mara vacuum-mode separator or the ritu gas-filled separator, and other ancillary devices.

Spectroscopy of the proton drip-line nucleus 203Fr

The nucleus 203Fr has been studied through γ -ray and electron spectroscopy, using the recoil-decay tagging technique. A 13/2+ state, with a half-life of 0.37(5) μs, has been observed in 203Fr. Both the α-decay branch and the internal de-excitation of the 1/2+ isomer in 203Fr have been studied. Furthermore, the corresponding 1/2+ state, with a half-life of 0.31(8) s, has been found in 199At. In addition, transitions feeding the 9/2− ground state of 203Fr have been identified. The observed level pattern suggests that the ground state is still spherical. peerReviewed

Octupole correlations in the structure of 0$_2^+$ bands in the N=88 nuclei 150Sm and 152Gd

Knowledge of the exact microscopic structure of the 01 + ground state and first excited 02 + state in 150Sm is required to understand the branching of double β decay to these states from 150Nd. The detailed spectroscopy of 150Sm and 152Gd has been studied using (α,xn) reactions and the γ -ray arrays AFRODITE and JUROGAM II. Consistently strong E1 transitions are observed between the excited Kπ = 02 + bands and the lowest negative parity bands in both nuclei. These results are discussed in terms of the possible permanent octupole deformation in the first excited Kπ = 02 + band and also in terms of the “tidal wave” model of Frauendorf. peerReviewed

Evolution of collective motion in light polonium nuclei

The {gamma}-ray spectroscopy of even- and odd-mass isotopes of polonium have been studied using arrays of Ge detectors coupled to recoil-mass analyzers, including recoil-decay tagging techniques. The level energies and B(E2) branching ratios can be reproduced by theoretical frameworks which do not explicitly include proton particle-hole excitations across the Z = 82 shell, conclusions in contrast to those deduced from alpha-decay measurements.

Confirmation of the new isotope 178Pb

The extremely neutron-deficient isotope 178Pb has been produced. The GREAT spectrometer at the focal plane position of the gas-filled separator RITU was used to study the α decay of 178Pb and its α-decay chain through α-α correlations. The α decay was measured to have an energy and half-life of Eα= 7610(30) keV and t1/2 = 0.21+0.21 −0.08 ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and proximity potential model. The α-decay reduced width and hindrance factor for 178Pb were deduced and correspond to an unhindered l = 0 transition. In addition, the mass excess of 178Pb and the α-decay Q value were calculated from the experimental results…

Lifetime measurement of the first excited 2+ state in 112Te

The lifetime of the 2+ → 0+ g.s. transition in the neutron-deficicient nucleus 112Te has been measured for the first time using the DPUNS plunger and the recoil distance Doppler shift technique. The deduced value for the reduced transition probability is B(E2 :0+ g.s. → 2+) = 0.46 ± 0.04 e2b2, indicating that there is no unexpected enhancement of the B(E2 :0+ g.s. → 2+) values in Te isotopes below the midshell. The result is compared to and discussed in the framework of large-scale shell-model calculations. peerReviewed

Identification of the Jπ = 1− state in 218Ra populated via α decay of 222Th

The α decay of 222Th populating the low-lying J π = 3− state, and also a proposed 1− state, in 218Ra has been observed. The observations suggest an excitation energy of 853 keV for the 1− state, which is 60 keV above the 3− state. The hindrance factors of these α decays give a possible boundary to the region of ground-state octupole deformation in the light-actinide nuclei. The relative positions of the J π = 1− and 3− states suggest they are produced by an octupole-vibrational mechanism, as opposed to α clustering or rotations of a reflection-asymmetric octupole-deformed shape. peerReviewed

A time-of-flight correction procedure for fast-timing data of recoils with varying implantation positions at a spectrometer focal plane

Abstract Fast-timing measurements at the focal plane of a separator can suffer from poor timing resolution. This is due to the variations in time-of-flight (ToF) for photons travelling to a given detector, which arise from the changes in the implantation positions of the recoil nuclei emitting the γ rays of interest. In order to minimise these effects on timing measurements, a procedure is presented that improves fast-timing data by performing ToF corrections on an event-by-event basis. This method was used to correct data collected with an array of eight LaBr 3 detectors, which detected γ rays from spatially distributed 138Gd recoil-implants at the focal plane of the Recoil-Ion-Transport-U…

Spectroscopy of 161Hf from low to high spin

Excited states in the neutron-deficient nucleus 161 72Hf89 have been populated using the 118Sn(48Ti,5n) 161Hf and 110Pd(56Fe,5n) 161Hf fusion-evaporation reactions at 240 and 270 MeV, respectively. The level scheme for 161Hf has been extended with the observation of new band structures and an I π = (13/2+) isomeric state with a half-life of 4.8(2) μs has been identified. The decay path from this isomer to the (7/2−) ground state is established. The yrast band, based on the (13/2+) isomeric state, is extended up to (73/2+) and side band structures are identified up to (69/2−) and (55/2−). Quasiparticle assignments for these rotational structures are made on the basis of their alignment prope…

Excited states and reduced transition probabilities in Os168

The level scheme of the neutron-deficient nuclide 168Os has been extended and mean lifetimes of excited states have been measured by the recoil distance Doppler-shift method using the JUROGAM \gamma-ray spectrometer in conjunction with the IKP K\"oln plunger device. The 168Os \gamma rays were measured in delayed coincidence with recoiling fusion-evaporation residues detected at the focal plane of the RITU gas-filled separator. The ratio of reduced transition probabilities B(E2;4_1^+ \rightarrow 2_1^+)/B(E2;2_1^+ \rightarrow 0_1^+) is measured to be 0.34(18), which is very unusual for collective band structures and cannot be reproduced by IBM-2 model calculations based on the SkM* energy-den…

Gamma-ray spectroscopy of 192–195Po

Prompt and delayed γ-rays have been observed from very neutron deficient 192–195Po nuclei by using the recoil-decay tagging (RDT) and recoil gating techniques. The yrast levels up to the (10+) state in the 192Po were identified for the first time. Comprehensive data for 194Po rendered it possible to extend the yrast line and to observe several positive and negative parity non-yrast states. In the odd-mass isotopes 193Po and 195Po, favoured and unfavoured states on top of the 13/2+ state have been identified. The results are discussed within the simple vibrator and rotor pictures as well as in the framework of coexisting spherical and deformed-intruder structures.

Reduced transition probabilities along the yrast line in 166W

Lifetimes of excited states in the yrast band of the neutron-deficient nuclide 166W have been measured utilizing the DPUNS plunger device at the target position of the JUROGAM II γ -ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal-plane spectrometer. Excited states in 166W were populated in the 92Mo(78Kr,4p) reaction at a bombarding energy of 380 MeV. The measurements reveal a low value for the ratio of reduced transitions probabilities for the lowest-lying transitions B(E2; 4+ → 2+)/B(E2; 2+ → 0+) = 0.33(5), compared with the expected ratio for an axially deformed rotor (B4/2 = 1.43). peerReviewed

Experimental investigation of the 0⁺₂ band in ¹⁵⁴Sm as a β-vibrational band

First prompt in-beam gamma-ray spectroscopy of a superheavy element: the 256Rf

Using state-of-the-art γ-ray spectroscopic techniques, the first rotational band of a superheavy element, extending up to a spin of 20 ¯h, was discovered in the nucleus 256Rf. To perform such an experiment at the limits of the present instrumentation, several developments were needed. The most important of these developments was of an intense isotopically enriched 50Ti beam using the MIVOC method. The experimental set-up and subsequent analysis allowed the 256Rf ground-state band to be revealed. The rotational properties of the band are discussed and compared with neighboring transfermium nuclei through the study of their moments of inertia. These data suggest that there is no evidence of a…

Octupole correlations in the structure of02+bands in theN=88nuclei150Sm and152Gd

Knowledge of the exact microscopic structure of the 0${}_{1}$${}^{+}$ ground state and first excited 0${}_{2}$${}^{+}$ state in ${}^{150}$Sm is required to understand the branching of double \ensuremath{\beta} decay to these states from ${}^{150}$Nd. The detailed spectroscopy of ${}^{150}$Sm and ${}^{152}$Gd has been studied using (\ensuremath{\alpha},xn) reactions and the \ensuremath{\gamma}-ray arrays AFRODITE and JUROGAM II. Consistently strong $E$1 transitions are observed between the excited ${K}^{\ensuremath{\pi}}$ $=$ 0${}_{2}$${}^{+}$ bands and the lowest negative parity bands in both nuclei. These results are discussed in terms of the possible permanent octupole deformation in the …

Fine structure in the α decay of 156Lu and 158Ta

Fine structure in the α decay of high-spin states in 156Lu and 158Ta has been identified by means of αγ - coincidence analysis. One new α decay from 156Lu and two from 158Ta were identified, one of which was found to populate a previously unknown state in 154Lu. The hindrance-factor systematics from all four odd-odd, N = 85 nuclei with known α-decaying, πh11/2 coupled states were reviewed and are discussed. These proved consistent with the previously assigned (πh11/2νh9/2 )10+ configuration of the α-decaying state in 156Lu, which differs from the (πh11/2ν f7/2 )9+ assignments in the other three nuclei. peerReviewed

Coexistence of triaxial and prolate shapes in 171Ir

Abstract Excited states in 171Ir have been observed for the first time. Gamma-rays were assigned to the nucleus by the recoil-decay tagging method. The ground-state band has a structure consistent with an h 11 2 proton coupled to a core of large triaxial deformation. At high spins, a bandcrossing occurs which is interpreted as a change in shape to a prolate deformation. Band-mixing calculations are performed for 171–175Ir. These show that shape-coexistence between triaxial and prolate states in these nuclei follows the same systematics found in their Pt and Os neighbours. The systematics are also compared with deformations calculated for 171–179Ir using the code “Ultimate Cranker”. Dipole b…

Spectroscopy on the proton drip-line: Probing the structure dependence of isospin nonconserving interactions

J. Henderson et al. ; 4 pags. ; 4 figs. ; PACS number(s): 21.10.Re, 21.60.Cs, 23.20.Lv, 27.50.+e

Microsecond isomers in 187Tl and 188Pb

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between 155Gd and 36Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the 159Tb(32S, 4n) reaction the γ-decay of isomeric levels in 187Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in…

Collective 2$^{+1}$ excitations in$^{206}$Po and$^{208,210}$Rn

In the present study, $B(E2; 2^{+}_{1}\rightarrow 0^{+}_{1})$ values have been measured in the 208,210Rn and 206Po nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. These nuclei have been proposed to lie in, or at the boundary of the region where the seniority scheme should persist. However, contributions from collective excitations are likely to be present when moving away from the N=126 closed shell. Such an effect is confirmed by the observed increased collectivity of the $2^{+}_{1}\rightarrow 0^{+}_{1}$ transitions. Experimental results have been interpreted with the aid of theoretical studies carried out within the BCS-based QRP…

Investigation of nuclear collectivity in the neutron mid-shell nucleusPb186

For the first time, non-yrast structures of the neutron mid-shell nucleus $^{186}\mathrm{Pb}$ have been identified in an in-beam \ensuremath{\gamma}-ray spectroscopy measurement using the recoil-decay tagging technique. The yrast band has been tentatively extended up to ${I}^{\ensuremath{\pi}}=20{}^{+},$ revealing a similar backbend to that observed in the Pt and Hg isotones. Three new bands and several other transitions have been observed. Calculations carried out in the framework of the interacting boson model together with mean-field studies using the generator coordinate method provide arguments for the association of one of the new bands with an oblate shape. The present data also show…

Investigation of the Δn = 0 selection rule in Gamow-Teller transitions: The β-decay of 207Hg

5 pags., 3 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0

In-beam andα-decay spectroscopy of191Poand evidence for triple shape coexistence at low energy in the daughter nucleus187Pb

Prompt gamma rays have been observed for the first time from the neutron-deficient nucleus Po-191 using the recoil-decay tagging technique at the RITU gas-filled separator. In addition improved alp ...

Evidence for oblate structure inPb186

In-beam $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data have been collected for $^{186}\mathrm{Pb}$ by combining the JUROGAM Ge-detector array and the GREAT spectrometer with the RITU gas-filled recoil separator for recoil-decay tagging measurements. In addition to the known prolate yrast band in $^{186}\mathrm{Pb}$, these data have enabled a new low-lying side band to be identified. Based on the analysis of its decay pattern and comparison with Interacting Boson Model (IBM) calculations, the new band is associated with an oblate shape.

Evolution from γ -soft to stable triaxiality in Nd136 as a prerequisite of chirality

The level structure of Nd136 has been investigated using the Mo100(Ar40,4n) reaction and the JUROGAM II+RITU+GREAT setup. The level scheme has been extended significantly. Many new bands have been identified both at low and high spin, among which are five nearly degenerate bands interpreted as chiral partners. Excitation energies, spins, and parities of the previously known bands are revised and firmly established, and some previously known bands have been revised. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. The band structure of Nd136 is now clarified and the various types of single-particle and collective excitations are well underst…

Recoil-decay tagging study of 205Fr

The nucleus 205Fr has been studied through γ -ray and electron spectroscopy using the recoil-decay tagging technique. The resulting level scheme presents a spherical structure built on the 9/2− ground state and a rotational structure on top of a short-lived isomer. The isomer, with a spin and parity of 13/2+ and a half-life of 80(20) ns, de-excites by an M2 transition directly to the 9/2− ground state. Another, longer-lived, isomer, with a half-life of 1.15(4) ms, has also been found and assigned a spin and parity of 1/2+. Transitions populating and de-exciting this isomer have been observed as well. peerReviewed

Evidence of chiral bands in even-even nuclei

Evidence for chiral doublet bands has been observed for the first time in the even-even nucleus 136 Nd . One chiral band was firmly established. Four other candidates for chiral bands were also identified, which can contribute to the realization of the multiple pairs of chiral doublet bands ( M χ D ) phenomenon. The observed bands are investigated by the constrained and tilted axis cranking covariant density functional theory (TAC-CDFT). Possible configurations have been explored. The experimental energy spectra, angular momenta, and B ( M 1 ) / B ( E 2 ) values for the assigned configurations are globally reproduced by TAC-CDFT. Calculated results support the chiral interpretation of the o…

Prompt and delayed spectroscopy of 199At

The neutron-deficient nucleus At199 has been studied through γ-ray and electron spectroscopy, using the recoil-decay tagging technique. Two experiments were conducted, using a gas-filled recoil separator with a focal-plane spectrometer alone and together with a germanium-detector array at the target position. The resulting level scheme for At199 includes a new isomer with a half-life of 0.80(5) μs and a spin and parity of (29/2+). The 13/2+ isomer, which de-excites via an M2 transition to the 9/2− ground state, was measured to have a half-life of 70(20) ns. Our earlier version of the level scheme for At197 has been updated as well. peerReviewed

Spectroscopy ofAt201including the observation of a shears band and the29/2+isomeric state

The excited states of $^{201}\mathrm{At}$ were studied and an isomeric $29/{2}^{+}$ state $[{T}_{\textonehalf{}}=3.39(9)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}]$ was identified by using a fusion-evaporation reaction, a gas-filled recoil separator, and recoil gating techniques. The $29/{2}^{+}$ state is suggested to originate from the $\ensuremath{\pi}({h}_{9/2})\ensuremath{\bigotimes}|^{200}\mathrm{Po};{11}^{\ensuremath{-}}\ensuremath{\rangle}$ configuration, and it decays through the 269- and 339-keV $E2$- and $E3$-type transitions, respectively. Moreover, a cascade of magnetic dipole transitions that is suggested to originate from a shears band was observed by using recoil-…

Reassigning the shapes of the 0+ states in the 186Pb nucleus

Across the physics disciplines, the 186Pb nucleus is the only known system, where the two first excited states, together with the ground state, form a triplet of zero-spin states assigned with prolate, oblate and spherical shapes. Here we report on a precision measurement where the properties of collective transitions in 186Pb were determined in a simultaneous in-beam γ-ray and electron spectroscopy experiment employing the recoil-decay tagging technique. The feeding of the 0+2 state and the interband 2+2→2+1 transition have been observed. We also present direct measurement of the energies of the electric monopole transitions from the excited 0+ states to the 0+ ground state. In contrast to…

A charge plunger device to measure the lifetimes of excited nuclear states where transitions are dominated by internal conversion

Abstract A charge plunger device has been commissioned based on the DPUNS plunger (Taylor et al., 2013) using the in-flight mass separator MARA at the University of Jyvaskyla. The 152 Sm (32 S ,4 n )180 Pt reaction was used to populate excited states in 180 Pt . A lifetime measurement of the 2 1 + state was performed by applying the charge plunger technique, which relies on the detection of the charge state-distribution of recoils rather than the detection of the emitted γ rays. This state was a good candidate to test the charge plunger technique as it has a known lifetime and depopulates through a converted transition that competes strongly with γ -ray emission. The lifetime of the 2 1 + s…

Direct observation of theBa114→Xe110→Te106→Sn102tripleα-decay chain using position and time correlations

The triple $\ensuremath{\alpha}$-decay chain $^{114}\mathrm{Ba}\ensuremath{\rightarrow}^{110}\mathrm{Xe}\ensuremath{\rightarrow}^{106}\mathrm{Te}\ensuremath{\rightarrow}^{102}\mathrm{Sn}$ has been directly observed for the first time, following the $^{58}\mathrm{Ni}(^{58}\mathrm{Ni},2n)$ reaction. Implantation of $^{114}\mathrm{Ba}$ nuclei into a double-sided silicon-strip detector has allowed their $\ensuremath{\alpha}$ decays to be correlated in position and time with the $\ensuremath{\alpha}$ decays of the daughter $(^{110}\mathrm{Xe})$ and granddaughter $(^{106}\mathrm{Te})$ nuclei. In total, 17 events have been assigned to the $^{114}\mathrm{Ba}\ensuremath{\rightarrow}^{110}\mathrm{Xe}…

In-beam spectroscopic studies of shape coexistence and collectivity in the neutron-deficientZ≈ 82 nuclei

In the present paper we focus on studies of shape coexistence in even-mass nuclei in the neutron-deficient Pb region. They are based on experiments carried out using tagging techniques in the Accelerator Laboratory of the University of Jyväskylä, Finland. Excited states in many of these nuclei can only be accessed via fusion-evaporation reactions employing high-intensity stable-ion beams. The key features in these experiments are high selectivity, clean spectra and instrumentation that enables high count rates. We review three spectroscopic highlights in this region. peerReviewed

Search for the terminating 27- state in 140Nd

In the search for the fully aligned 27− state in 140Nd predicted by cranked Nilsson-Strutinsky calculations, new close-to-spherical high-spin states have been discovered. Both the close-to-spherical and the triaxial calculated states are in good agreement with the experimental results, supporting the existence of shape coexistence up to very high spins. Shell-model calculations using a newly developed effective interaction for the 50 N ,Z 82 mass region are in good agreement with the observed spherical states. The comparison between the experimental and calculated level energies allowed the relative energy to be established between several proton and neutron orbitals at high energy and spin…

Coulomb excitation of re-accelerated 208Rn and 206Po beams

In the present study, B( E2; 2(+)-> 0(+) ) values have been measured in the Rn-208 and Po-206 nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. The resulting B(E2; 2(+)-> 0(+)) in 208Rn is similar to 0.08 e(2)b(2). These nuclei lie in, or at the boundary of the region where seniority scheme should persist. However, contributions from collective excitations may be present when moving away from the N = 126 shell closure. To date, surprisingly little is known of the transition probabilities between the low-spin states in this region.

Towards saturation of the electron-capture delayed fission probability: The new isotopes $^{240}Es$ and $^{236}Bk$

Abstract The new neutron-deficient nuclei 240 Es and 236 Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240 Es produced in the fusion–evaporation reaction 209 Bi( 34 S,3n) 240 Es. Half-lives of 6 ( 2 ) s and 22 − 6 + 13 s were obtained for 240 Es and 236 Bk, respectively. Two groups of α particles with energies E α = 8.19 ( 3 ) MeV and 8.09 ( 3 ) MeV were unambiguously assigned to 240 Es. Electron-capture delayed fission branches with probabilities of 0.16 ( 6 ) and 0.04 ( 2 ) were measured for 240 Es and 236 Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilitie…

In-beam γ -ray spectroscopy of low- and medium-spin levels in Po211

The structure of the low- and medium-spin levels of the $^{211}\mathrm{Po}$ nucleus have been studied with in-beam $\ensuremath{\gamma}$-ray spectroscopy with the $^{208}\mathrm{Pb}(\ensuremath{\alpha},n)^{211}\mathrm{Po}$ fusion-evaporation reaction. The level scheme was further extended with levels of the configurations $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{8}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{11/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensurem…

COMMISSIONING OF THE SPEDE SPECTROMETER WITH STABLE BEAMS

The SPectrometer for Electron DEtection (SPEDE) has been constructed for in-beam nuclear structure studies using radioactive ion beams. SPEDE employs a silicon detector for detecting conversion electrons. It is designed to be used in conjunction with the MINIBALL spectrometer at HIE-ISOLDE, CERN. Peer reviewed

Identification of excited states in doubly odd63140Eu77by recoil-isomer tagging

The 36Ar + 107Ag fusion-evapn. reaction was used to search for isomeric states in the N = 77 isotope 140Eu near the proton-drip line. The recoiling nuclei were implanted into a Si detector, at the focal plane of a gas-filled separator, where prompt and delayed g-ray transitions were correlated across isomeric states using recoil-isomer tagging. The feeding and decay of a new 299(3) ns isomeric state was established. This measurement represents the first observation of excited high-spin states in 140Eu. The behavior of the new states above the isomer is discussed in terms of theor. calcns. based upon the cranked-shell model and upon the exptl. systematics of other N = 77 isotones. Within thi…

Spectroscopic factor and proton formation probability for the d3/2 proton emitter 151Lu

The quenching of the experimental spectroscopic factor for proton emission from the short-lived $d_{3/2}$ isomeric state in $^{151m}$Lu was a long-standing problem. In the present work, proton emission from this isomer has been reinvestigated in an experiment at the Accelerator Laboratory of the University of Jyv\"{a}skyl\"{a}. The proton-decay energy and half-life of this isomer were measured to be 1295(5) keV and 15.4(8) $\mu$s, respectively, in agreement with another recent study. These new experimental data can resolve the discrepancy in the spectroscopic factor calculated using the spherical WKB approximation. Using the R-matrix approach it is found that the proton formation probabilit…

Spectroscopy of transfermium nuclei: No-252(102)

An in-beam study of excited states in the transfermium nucleus 252 No has been performed using the recoil separator RITU together with the JUROSPHERE II array at the University of Jyväskylä. This is the second transfermium nucleus studied in an in-beam experiment. Levels up to spin 20 were populated and compared to levels in 254 No . An upbend is seen at a frequency of 200 keV/ħ corresponding to spin 16. We also use an improved systematics to connect the energy of the lowest 2 + state with its half-life and find that the deformation of both 2 5 2 , 2 5 4 No is slightly larger than previously assumed. peerReviewed

Identification of a dipole band above the Iπ = 31/2- isomeric state in 189Pb

A dipole band of six transitions built upon a firmly established I π = 31/2− isomeric state has been identified in 189Pb using recoil-isomer tagging. This is the lightest odd-mass Pb nucleus in which a dipole band is known. The dipole nature of the new transitions has been confirmed through angular-intensity arguments. The evolution of the excitation energy and the aligned-angular momentum of the states in the new dipole band are compared with those of dipole bands in heavier, odd-mass lead isotopes. This comparison suggests that the new band in 189Pb is based upon a π[s−2 1/2h9/2i13/2]11− ⊗ ν[i −1 13/2+ ]13/2+ configuration. However, the increased aligned-angular momentum in 189Pb may sugg…

Lifetime measurements in 166Re : Collective versus magnetic rotation

WOS: 000371740600004

Low-lying structure of light radon isotopes

The excited states in the neutron-deficient isotopes Rn have been populated using the Er(Ar,4n), Er(Ar,4n), and Er(Ar,4n) reactions at beam energies of 175, 182, and 177 MeV, respectively. Evaporation residues were selected using an in-flight gas-filled separator and implanted at the focal plane into a 16-element position-sensitive, passivated ion-implanted planar silicon detector. Prompt γ rays were observed at the target position using an array of Compton-suppressed germanium detectors. Correlation with the subsequent radioactive decay of associated recoiling ions in the silicon detector, recoil-γ and recoil-γ-γ coincidences were used to construct decay schemes of light radon isotopes. Me…

Quasiparticle alignments and α-decay fine structure of 175Pt

Excited states and decay properties of 175Pt have been investigated using the 92Mo(86Sr,2pn) fusion-evaporation reaction. The JUROGAM I γ -ray spectrometer and the GREAT spectrometer were used in conjunction with the gas-filled recoil separator RITU for the measurement of the radiation at the target and focal plane positions, respectively. Two new band structures, assigned to be based on the I π = (7/2 −) ground state in 175Pt, have been established and the known yrast band has been extended up to I π = (49/2 +). Rotational properties of the excited states in 175Pt have been investigated within the cranked shell-model formalism. The low-frequency changes in the alignments of the positive- a…

Competing Decay Modes of a High-spin Isomer in the Proton-unbound Nucleus 158Ta

An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both α and γ decay modes. The large spin change required to decay via γ-ray emission incurs a lifetime long enough for α decay to compete. The α decay has an energy of 8644(11) keV, which is among the highest observed in the region, a partial half-life of 440(70) µs and changes the spin by 11~. In this paper, additional evidence supporting the assignment of this α decay to the high-spin isomer in 158Ta will be presented. peerReviewed

Collectivity ofPo196at low spin

Absolute electromagnetic transition probabilities in $^{196}\mathrm{Po}$ have been measured using the recoil distance Doppler-shift technique. The lifetimes of the three lowest yrast states in $^{196}\mathrm{Po}$ were extracted from singles \ensuremath{\gamma}-ray spectra by using the recoil-decay tagging method. In addition, configuration mixing calculations of angular momentum projected mean-field states have been carried out for $^{196}\mathrm{Po}$. The present study sheds light on the onset of collectivity and mixing of competing structures in neutron-deficient Po nuclei.

Direct observation of the Ba 114 → Xe 110 → Te 106 → Sn 102 triple α -decay chain using position and time correlations

The triple α-decay chain 114Ba → 110Xe → 106Te → 102Sn has been directly observed for the first time, following the 58Ni(58Ni ,2n) reaction. Implantation of 114Ba nuclei into a double-sided silicon-strip detector has allowed their α decays to be correlated in position and time with the α decays of the daughter (110Xe) and granddaughter (106Te) nuclei. In total, 17 events have been assigned to the 114Ba → 110Xe → 106Te → 102Sn triple α-decay chain. The energy of the 114Ba α decay has been measured to be Eα = 3480(20) keV, which is 70 keV higher than the previously measured value, and the half-life of 114Ba has been measured with improved accuracy, to be 380+190 −110 ms. A revised Q12C value …

Experimental study of isomeric intruder ½+ states 197,203At

A newly observed isomeric intruder ½ + state [ T ½ = 3.5 ( 6 ) ms ] is identified in 203 At using a gas-filled recoil separator and fusion-evaporation reactions. The isomer is depopulated through a cascade of E 3 and mixed M 1 / E 2 transitions to the 9 / 2 − ground state, and it is suggested to originate from the π ( s ½ ) − 1 configuration. In addition, the structures above the ½ + state in 203 At and 197 At are studied using in-beam γ -ray spectroscopy, recoil-decay tagging, and recoil-isomer decay tagging methods. The ½ + state is fed from 3 / 2 + and 5 / 2 + states, and the origin of these states are discussed. peerReviewed

Spectroscopy of Kr70 and isospin symmetry in the T=1 fpg shell nuclei

The recoil-β tagging technique has been used in conjunction with the 40 Ca(32 S ,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2 + and, tentatively, 4 + states in the nucleus 70 Kr. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J = 0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectation for analog states th…

Transition probability studies in 175Au

Transition probabilities have been measured between the low-lying yrast states in 175Au by employing the recoil distance Doppler-shift method combined with the selective recoil-decay tagging technique. Reduced transition probabilities and magnitudes of transition quadrupole moments have been extracted from measured lifetimes allowing dramatic changes in nuclear structure within a low excitation-energy range to probed. The transition quadrupole moment data are discussed in terms of available systematics as a function of atomic number and aligned angular momentum. peerReviewed

Decay of a 19− isomeric state in 156Lu

A multiparticle spin-trap isomeric state having a half-life of 179(4) ns and lying 2601 keV above the yrast 10 + state in 156 Lu has been discovered. The 156 Lu nuclei were produced by bombarding isotopically enriched 106 Cd targets with beams of 58 Ni ions, separated in flight using the gas-filled separator RITU and their decays were measured using the GREAT spectrometer. Analysis of the main decay path that populates yrast states observed previously suggests a spin-parity assignment of 19 − for the isomeric state, which is consistent with isomeric states identified in the N = 85 isotones. Comparison with other decay paths in 156 Lu indicates that the [ π h − 1 11 / 2 ⊗ ν h 9 / 2 ] 10 + st…

Observation of the proton emitter 116,57La59

The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental “smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope 11657La59, 23 neutrons away from the only stable isotope 13957La82, is re…

Multiparticle configurations of excited states in 155Lu

Excited states in the neutron-deficient N=84 nuclide 155Lu have been populated by using the 102Pd(58Ni,αp) reaction. The 155Lu nuclei were separated by using the gas-filled recoil ion transport unit (RITU) separator and implanted into the Si detectors of the gamma recoil electron alpha tagging (GREAT) spectrometer. Prompt γ-ray emissions measured at the target position using the JUROGAM Ge detector array were assigned to 155Lu through correlations with α decays measured in GREAT. Structures feeding the (11/2−) and (25/2−)α-decaying states have been revised and extended. Shell-model calculations have been performed and are found to reproduce the excitation energies of several of the low-lyin…

Collectivity in the light radon nuclei measured directly via Coulomb excitation

Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron midshell at N=104. Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy, and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of Rn202 and Rn…

Probing the shape of 176Hg along the yrast line

In-beam γ-ray and γ-γ coincidence measurements have been made for the very neutron-deficient nucleus 176Hg using the recoil-decay tagging (RDT) technique. The irregular yrast sequence observed up to I=10ħ indicates that the prolate intruder band, seen in heavier Hg isotopes near the neutron midshell, crosses the nearly spherical ground-state band of 176Hg above I=6ħ. peerReviewed

Highly deformed bands in Nd nuclei: New results and consistent interpretation within the cranked Nilsson-Strutinsky formalism

International audience; Three new highly-deformed (HD) bands are identified in Nd136 and the highly deformed band of Nd137 is extended at higher spin by four transitions, revealing a band crossing associated with the occupation of the second νi13/2 intruder orbital. Extended cranked Nilsson-Strutinsky calculations are performed for all HD bands observed in Nd134, Nd136, and Nd137, achieving for the first time a consistent interpretation of all HD bands in the Nd nuclei. The new interpretation has significant consequences, like the change of parity of the yrast HD bands of Nd134 and Nd136, and the involvement of two negative-parity neutron intruder orbitals in the configurations of most HD b…

Lifetime measurements of lowest states in the π g7/2 ⊗ νh11/2 rotational band in 112I

A differential-plunger device was used to measure the lifetimes of the lowest states in the πg7/2 ⊗ νh11/2 rotational band in doubly odd 112I with the 58Ni(58Ni, 3pn) reaction. A differential decay curve method was performed using the fully shifted and degraded γ -ray intensity measurements as a function of target-to-degrader distance. The lifetimes of the lowest three states in the πg7/2 ⊗ νh11/2 band in 112I were measured to be 124(30), 130(25), and 6.5(5) ps, respectively. As the lifetimes of successive excited states in a rotational band are expected to decrease with increasing excitation energy, these measurements suggest that the order of the transitions in the established band in 112…

Identification of a 6.6μs isomeric state in 175Ir

An experiment has been performed to study excited states in the neutron-deficient nucleus 175Ir via the use of the JUROGAM II high-purity germanium detector array and the RITU gas-filled separator at JYFL, Jyväskylä. By using isomer tagging, an isomeric state with a half-life of 6.58(15) μs has been observed in 175Ir for the first time. It has been established that the isomer decays via a 45.2 (E1)–26.1 (M1) keV cascade to new states below the previously reported ground state in 175Ir with Iπ = (5/2−). We now reassign this (5/2−) state to the isomeric state discovered in this study. peerReviewed

In-beam study of 253No using the SAGE spectrometer

The heavy actinide nucleus 253No (Z = 102) was studied using the (S)ilicon (A)nd (Ge)rmanium (SAGE) spectrometer allowing simultaneous in-beam $\gamma$ -ray and conversion electron spectroscopy at the accelerator laboratory of the University of Jyvaskyla. Using the recoil-tagging technique, $\gamma$ -electron coincidences have allowed for the extension of the level scheme in the lower-spin region of the yrast band. In addition, internal conversion coefficient (ICC) measurements to establish the multipolarity of transitions have been performed. Measurement of the interband-intraband branching ratios supports the assignment of the Nilsson band-head configuration $9/2^{-}[734]$ assigned in pre…

Determination of absolute internal conversion coefficients using the SAGE spectrometer

A non-reference based method to determine internal conversion coefficients using the SAGE spectrometer is carried out for transitions in the nuclei of 154Sm, 152Sm and 166Yb. The Normalised-Peak-to-Gamma method is in general an efficient tool to extract internal conversion coefficients. However, in many cases the required well-known reference transitions are not available. The data analysis steps required to determine absolute internal conversion coefficients with the SAGE spectrometer are presented. In addition, several background suppression methods are introduced and an example of how ancillary detectors can be used to select specific reaction products is given. The results obtained for …

Deformation of the proton emitter 113Cs from electromagnetic transition and proton-emission rates

The lifetime of the (11/2+) state in the band above the proton-emitting (3/2+) state in 113Cs has been measured to be τ = 24(6) ps from a recoil-decay-tagged differential-plunger experiment. The measured lifetime was used to deduce the deformation of the states using wave functions from a nonadiabatic quasiparticle model to independently calculate both proton-emission and electromagnetic γ -ray transition rates as a function of deformation. The only quadrupole deformation, which was able to reproduce the experimental excitation energies of the states, the electromagnetic decay rate of the (11/2+) state and the proton-emission rate of the (3/2+) state, was found to be β2 = 0.22(6). This defo…

Level structure above the 17+ isomeric state in 152 69 Tm83

Excited states above the 17+ isomeric state in the proton-rich nucleus 152Tm were established by employing the recoil-isomer tagging technique. Data were collected using the JUROGAM gamma-ray array and the GREAT spectrometer together with the recoil ion transport unit (RITU) gas-filled recoil separator and analyzed to identify the prompt and delayed γ decays from the levels in 152Tm. Shell-model calculations, either in a large valence space or in a reduced model space with five protons in the π0h11/2 orbital and one neutron in the ν1f7/2 orbital, agree with the observed energies of the yrast levels up to angular momentum J = 21. The observation of near degeneracies in the energy spectrum ca…

High-spin study of neutron-deficient $^{114}$Xe

Abstract High-spin states have been populated in 114 54 Xe via the 58 Ni( 58 Ni, 2p) reaction at 210 MeV, using the Jurosphere γ -ray spectrometer to record γ -ray coincidences. The known level scheme has been significantly extended and includes two positive-parity and three negative-parity structures. At the highest spins, one of the negative-parity bands becomes yrast and shows the characteristics of a smoothly terminating band. Quadrupole moments for two of the bands at high spin have been estimated through a Doppler-broadened lineshape analysis; the terminating band has a reduced quadrupole moment implying that it is not far from full termination into a noncollective oblate state. Extra…

Prompt and delayed spectroscopy ofAt199

The neutron-deficient nucleus $^{199}\mathrm{At}$ has been studied through $\ensuremath{\gamma}$-ray and electron spectroscopy, using the recoil-decay tagging technique. Two experiments were conducted, using a gas-filled recoil separator with a focal-plane spectrometer alone and together with a germanium-detector array at the target position. The resulting level scheme for $^{199}\mathrm{At}$ includes a new isomer with a half-life of 0.80(5) $\ensuremath{\mu}$s and a spin and parity of ($29/{2}^{+}$). The $13/{2}^{+}$ isomer, which de-excites via an $M2$ transition to the $9/{2}^{\ensuremath{-}}$ ground state, was measured to have a half-life of 70(20) ns. Our earlier version of the level s…

Alpha decay study of 218U; a search for the sub-shell closure at Z=92

Neutron-deficient uranium isotopes were studied via α spectroscopic methods. A low-lying α-decaying isomeric state was found in 218U. The new isomeric state was assigned spin and parity I π = 8+. The isomer decays by α emission with an energy E = 10678(17) keV and with a half-life T 1/2 = (0.56 -0.14 +0.26 ) ms. The known alpha-decay properties of the ground state of 218U was measured with improved statistics. The ground-state α-decay has an energy E = 8612(9) keV and a half-life T 1/2 = (0.51 -0.10 +0.17 ) ms.

Fine structure in the α decay of high-spin isomers in 155Lu and 156Hf

Fine structure in the α decay of high-spin isomers in 155Lu(25/2−) and 156Hf (8+) has been studied for the first time using αγ -coincidence analysis. Three new α decays from 155Lu(25/2−) and two from 156Hf (8+) have been identified, populating seniority s > 1 states in the N = 82 nuclei 151Tm and 152Yb, respectively. The reduced hindrance factors of the α decays support the previous configuration assignments of the populated states. This is the first observation of states with excitation energy greater than 1.5 MeV being populated following α decay in nuclei outside of the 208Pb region. peerReviewed

Enhancing the sensitivity of recoil-beta tagging

Tagging with β-particles at the focal plane of a recoil separator has been shown to be an effective technique for the study of exotic proton-rich nuclei. This article describes three new pieces of apparatus used to greatly improve the sensitivity of the recoil-beta tagging technique. These include a highly-pixelated double-sided silicon strip detector, a plastic phoswich detector for discriminating high-energy β-particles, and a charged-particle veto box. The performance of these new detectors is described and characterised, and the resulting improvements are discussed.

Detailed spectroscopy of Bi195

An experiment focused on the study of shape coexistence and new high-spin structures in $^{195}\mathrm{Bi}$ has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the $13/{2}^{+}$ isomeric state was extended up to ${I}^{\ensuremath{\pi}}=(49/{2}^{+})$ and an energy of 5706 keV. The ${I}^{\ensuremath{\pi}}=31/{2}^{+}$ member of the $\ensuremath{\pi}{i}_{13/2}$ band was also found to feed a new long-lived isomeric state with an excitation …

Single-particle and collective excitations in the transitional nucleus 166Os

The mean lifetimes of the lowest energy 2(+), 8(+) and 9(-) states in Os-166 have been measured using the recoil distance Doppler-shift method in conjunction with a selective recoil-decay tagging t ...

Excited states and reduced transition probabilities in Os 168

The level scheme of the neutron-deficient nuclide 168Os has been extended and mean lifetimes of excited states have been measured by the recoil distance Doppler-shift method using the JUROGAM γ -ray spectrometer in conjunction with the IKP Koln plunger device. The ¨ 168Os γ rays were measured in delayed coincidence with recoiling fusion-evaporation residues detected at the focal plane of the RITU gas-filled separator. The ratio of reduced transition probabilities B(E2; 4+ 1 → 2+ 1 )/B(E2; 2+ 1 → 0+ 1 ) is measured to be 0.34(18), which is very unusual for collective band structures and cannot be reproduced by interacting boson model (IBM-2) calculations based on the SkM* energy-density func…

Decay of a 19− isomeric state in Lu156

A multiparticle spin-trap isomeric state having a half-life of 179(4) ns and lying 2601 keV above the yrast 10(+) state in Lu-156 has been discovered. The Lu-156 nuclei were produced by bombarding ...

Lifetime measurements of lowest states in the πg7/2⊗νh11/2 rotational band in I112

γdecay of excited states in198Rnidentified using correlated radioactive decay

The low-lying level structure of the neutron-deficient isotope ${}^{198}\mathrm{Rn}$ has been studied for the first time, using the ${}^{166}\mathrm{Er}{(}^{36}\mathrm{Ar},4n)$ reaction at a beam energy of 175 MeV. Evaporation residues were selected using an in-flight gas-filled separator, RITU, and implanted at the focal plane into a 16-element position-sensitive, passivated ion-implanted planar silicon detector. Prompt $\ensuremath{\gamma}$ rays in ${}^{198}\mathrm{Rn}$ were observed at the target position using the JUROSPHERE array of 24 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the silicon detector. Is…

Single-particle and collective excitations in the transitional nucleus 166Os

The mean lifetimes of the lowest energy 2+, 8+ and 9− states in 166Os have been measured using the recoil distance Doppler-shift method in conjunction with a selective recoil-decay tagging technique. These measurements extend studies into the most neutron-deficient mass region accessible to current experimental methods. The B(E2; 2+ → 0+) = 7(2) W.u. extracted from these measurements is markedly lower than those observed in the heavier even-mass Os isotopes. The 8+ and 9− states yield reduced transition probabilities that are consistent with single-particle transitions. While these values may indicate a departure from collective structure, the level scheme and the underlying nuclear configu…

Lifetime measurement of the first excited2+state inTe112

The lifetime of the 2(+) --> 0(g.s.)(+) transition in the neutron-deficicient nucleus Te-112 has been measured for the first time using the DPUNS plunger and the recoil distance Doppler shift te ...

α decay of the πh11/2 isomer in Ir164

The α -decay branch of the πh 11 / 2 isomer in 164 Ir has been identified using the GREAT spectrometer. The 164 Ir nuclei were produced using the 92 Mo( 78 Kr ,p 5 n ) 164 Ir reaction and separated in flight using the recoil ion transport unit (RITU) gas-filled separator. The measured α -decay energy of 6880 ± 10 keV allowed the excitation of the πh 11 / 2 state in 160 Re to be deduced as 166 ± 14 keV. The half-life of 164 Ir was measured with improved precision to be 70 ± 10 μ sandan α -decay branching ratio of 4 ± 2% was determined. Improved half-life and branching ratio measurements were also obtained for 165 Ir, but no evidence was found for the ground-state decays of either 164 Ir or 1…

Spectroscopy of the neutron-deficient nuclide 171Pt

A number of previously unobserved gamma-rays emitted from the neutron-deficient nuclide Pt-171 have been identified using the recoil decay tagging technique. The level scheme has been updated using ...

Proton emission from an oblate nucleus 151Lu

Abstract Excited states in the proton-unbound nucleus 151Lu have been established using γ-ray coincidence techniques. The lifetime of the first excited state above the proton-emitting ground state has been measured using the recoil-distance Doppler-shift method combined with recoil-decay tagging. The experimental level scheme and extracted lifetime have been compared with state-of-the-art theoretical calculations based upon a non-adiabatic deformed Woods–Saxon potential. This comparison suggests that the proton-emitting ground state in 151Lu is mildly oblate with a deformation β = − 0.11 − 0.05 + 0.02 and represents the best evidence to date for proton emission from an oblate nucleus.

Decay spectroscopy of 179 82 Pb 97 and evidence for a 9/2− intruder state in 179 81 Tl 98

The very neutron-deficient isobars 179Pb and 179Tl have been produced using the fusion-evaporation reactions 104Pd(78Kr,xpyn), where x≤1 and y≥2. The gas-filled separator RITU was employed to transport and separate the recoiling nuclei of interest from the scattered beam and unwanted products. The GREAT spectrometer was used to study the decay properties through α−α and α−γ correlations, which has allowed the ground state of 179Pb to be assigned as Iπ=9/2−. The decay of 179Pb was measured to have an α-particle energy and half-life of Eα=7348(5)keV and t1/2=2.7(2) ms, respectively. A search for a νi13/2 state in 179Pb was performed, but only a limit of excitation energy and half-life was obt…

Recoil-decay tagging spectroscopy of 162 74 W 88

Excited states in the highly neutron-deficient nucleus 162W have been investigated via the 92Mo(78Kr, 2α) 162W reaction. Prompt γ rays were detected by the JUROGAM II high-purity germanium detector array and the recoiling fusion-evaporation products were separated by the recoil ion transport unit (RITU) gas-filled recoil separator and identified with the gamma recoil electron alpha tagging (GREAT) spectrometer at the focal plane of RITU. γ rays from 162W were identified uniquely using mother-daughter and mother-daughter-granddaughter α-decay correlations. The observation of a rotational-like ground-state band is interpreted within the framework of total Routhian surface (TRS) calculations, …

β decay studies of n-rich Cs isotopes with the ISOLDE Decay Station

R. Lica et al. -- 14 pags., 7 figs., tab. -- Open Access funded by Creative Commons Atribution Licence 3.0

Investigations into the alpha-decay of 195At

The low-energy nuclear structure and decay properties of the neutron-deficient isotopes 195At and 191Bi have been studied. 195At was produced in the reaction 142Nd(56Fe,p2n)195At and 191Bi as the daughter activity of 195At. The activities were implanted in a position-sensitive silicon detector after being separated from the primary beam by a gas-filled recoil separator. The 1/2+ intruder state was determined to be the ground state in 195At with an alpha-decay energy of E α = 6953(3) keV and a half-life T 1/2 = 328(20) ms. Another state with an alpha-decay energy E α = 7075(4) keV and a half-life T 1/2 = 147(5) ms was found to decay to a 148.7(5) keV excited state in 191Bi for which a spin a…

αdecay studies of the nuclides195Rnand196Rn

The new neutron deficient nuclide ${}^{195}\mathrm{Rn}$ and the nuclide ${}^{196}\mathrm{Rn}$ have been produced in fusion evaporation reactions using ${}^{56}\mathrm{Fe}$ ions on ${}^{142}\mathrm{Nd}$ targets. A gas-filled recoil separator was used to separate the fusion products from the scattered beam. The activities were implanted in a position sensitive silicon detector. The isotopes were identified using spatial and time correlations between implants and decays. Two $\ensuremath{\alpha}$ decaying isomeric states, with ${E}_{\ensuremath{\alpha}}=7536(11)\mathrm{keV}[{T}_{1/2}{=(6}_{\ensuremath{-}2}^{+3})\mathrm{ms}]$ for the ground state and ${E}_{\ensuremath{\alpha}}=7555(11)\mathrm{k…

In-beam study of 254No

Excited states of the Z = 102 nuclide 254No have been studied in the reaction 208Pb(48Ca,2n) by means of in-beam γ -ray spectroscopy in combination with recoil gating and recoil decay tagging. A Ge detector array, consisting of four clover detectors, and a gas-filled separator were used. Six γ-ray lines were observed and associated with E2 transitions in the ground state band of 254No, the highest-lying of these being the 16+→ 14+ transition. Based on global systematics and the extrapolated 2+ 1 excitation energy, the value β2= 0.27 ± 0.03 was extracted for the quadrupole deformation. An improved value for the half-life of 254No, T1/2= (48 ± 3) s, was determined.

Decay spectroscopy of Pb97182179 and evidence for a 9/2− intruder state in Tl98181179

The very neutron-deficient isobars Pb-179 and Tl-179 have been produced using the fusion-evaporation reactions Pd-104(Kr-78,xpyn), where x = 2. The gas-filled separator RITU was employed to transpo ...

Spectroscopy of193Bi

An experiment aiming to study the shape coexistence in 193Bi has been performed at the Accelerator laboratory of the University of Jyväskylä, Finland (JYFL). Many new states have been found, hugely extending the previously known level scheme of 193Bi. The Iπ=292+${I^\pi } = {{{29} \over 2}^ + }$ member of the πi13/2 band de-excites also to the previously, only tentatively placed long-lived isomeric state. This link determines the energy of the isomeric state to be 2260(1) keV and suggests a spin and parity of (272+)$\left( {{{{{27} \over 2}}^ + }} \right)$. The half-life of the isomeric state was measured to be 84.4(6) µs. A level structure on top of this isomeric state was constructed. How…

α-decay studies of the francium isotopes198Fr and199Fr

Very neutron deficient francium isotopes have been produced in fusion evaporation reactions using ${}^{60}$Ni ions on ${}^{141}$Pr targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two $\ensuremath{\alpha}$-particle activities, with ${E}_{\ensuremath{\alpha}}=7613(15)$ keV and ${T}_{1/2}$ $=$ (${15}_{\ensuremath{-}5}^{+12}$) ms and ${E}_{\ensuremath{\alpha}}=7684(15)$ keV and ${T}_{1/2}$ $=$…

Lifetime measurements of excited states in $^{163}$W and the implications for the anomalous B(E2) ratios in transitional nuclei

Grahn, Tuomas/0000-0002-6255-2279; Herzan, Andrej/0000-0002-6736-7638; Cullen, Dave/0000-0002-0041-1606; Barber, Liam/0000-0002-7409-9352; Keatings, James Michael/0000-0003-4271-8021; SAYGI, BAHADIR/0000-0001-5406-506X; Greenlees, Paul/0000-0002-5986-5274; Spagnoletti, Pietro/0000-0002-7674-989X; Parr, Edward/0000-0001-6204-4461; Bondili, S Nara Singh/0000-0002-4096-2429

γ-ray and decay spectroscopy of194,195,196At

Excited states of ${}^{195}$At have been studied by means of in-beam $\ensuremath{\gamma}$-ray spectroscopy and the recoil-decay tagging technique. A strongly coupled rotational band feeding the $\ensuremath{\alpha}$-decaying $7/{2}^{\ensuremath{-}}$ state via unobserved transitions was identified. This band is presumably built on the oblate proton ${I}^{\ensuremath{\pi}}=13/{2}^{+}$ state. Confirming earlier measurements, $\ensuremath{\alpha}$ decays from the $1/{2}^{+}$ and $7/{2}^{\ensuremath{-}}$ states were observed. Additionally, an $E3$ branch competing with the $\ensuremath{\alpha}$ decay of the $7/{2}^{\ensuremath{-}}$ state was inferred. Also $\ensuremath{\alpha}$ decays of the od…

Excited states in the proton-unbound nuclide 158Ta

Excited states in the neutron-deficient odd-odd proton-unbound nuclide 158Ta have been investigated in two separate experiments. In the first experiment, 166Ir nuclei were produced in the reactions of 380 MeV 78Kr ions with an isotopically enriched 92Mo target. The α-decay chain of the 9+ state in 166Ir was analyzed. Fine structure in the α decay of the 9+ state in 162Re established a 66 keV difference in excitation energy between the lowest-lying 9+ and 10+ states in 158Ta. Higher-lying states in 158Ta were populated in the reactions of 255 MeV 58Ni ions with an isotopically enriched 102Pd target. Gamma-ray decay paths that populate, depopulate, and bypass a 19− isomeric state have been id…

Fine structure in the α decay of high-spin isomers in Lu155 and Hf156

Fine structure in the a decay of high-spin isomers in Lu-155( 25/2(-)) and Hf-156(8(+))has been studied for the first time using alpha gamma- coincidence analysis. Three new a decays from Lu-155(25 ...

Lifetime measurements in 166Re : Collective versus magnetic rotation

Lifetimes of excited states in the neutron-deficient odd-odd nucleus 166Re have been measured for the first time using the recoil distance Doppler-shift method. The measured lifetime for the (8−) state; τ = 480 (80) ps, enabled an assessment of the multipolarities of the γ rays depopulating this state. Information on electromagnetic transition strengths were deduced for the γ -ray transitions from the (9−), (10−), and (11−) states, and in the case of the (10−) and (11−) states limits on the B(M1) and B(E2) strengths were estimated. The results are compared with total Routhian surface predictions and semiclassical calculations. Tilted-axis cranking calculations based on a relativistic mean-f…

Reinvestigation of the excited states in the proton emitter 151Lu : Particle-hole excitations across the N=Z=64 subshell

The excited states of the proton emitter 151Lu were reinvestigated in a recoil-decay tagging experiment at the Accelerator Laboratory of the University of Jyväskylä (JYFL). The level scheme built on the ground state of 151Lu was updated with five new γ -ray transitions. Large-scale shell model calculations were carried out in the model space consisting of the neutron and proton orbitals 0g7/2, 1d5/2, 1d3/2, 2s1/2, and 0h11/2 with the optimized monopole interaction in order to interpret the experimental level scheme of 151Lu. It is found that the excitation energies of states above the 27/2− and 23/2+ isomeric levels in 151Lu can be sensitive to excitations from g7/2 and d5/2 to single-parti…

Search for the terminating27−state inNd140

In the search for the fully aligned 27(-) state in Nd-140 predicted by cranked Nilsson-Strutinsky calculations, new close-to-spherical high-spin states have been discovered. Both the close-to-spherical and the triaxial calculated states are in good agreement with the experimental results, supporting the existence of shape coexistence up to very high spins. Shell-model calculations using a newly developed effective interaction for the 50 <= N, Z <= 82 mass region are in good agreement with the observed spherical states. The comparison between the experimental and calculated level energies allowed the relative energy to be established between several proton and neutron orbitals at high energy…

Alpha-decay studies of the nuclides 195Rn and 196Rn

The new neutron deficient nuclide 195 Rn and the nuclide 196 Rn have been produced in fusion evaporation reactions using 56 Fe ions on 142 Nd targets. A gas-filled recoil separator was used to separate the fusion products from the scattered beam. The activities were implanted in a position sensitive silicon detector. The isotopes were identified using spatial and time correlations between implants and decays. Two α decaying isomeric states, with E α = 7536 ( 11 ) keV [ T 1 / 2 = ( 6 + 3 − 2 ) ms ] for the ground state and E α = 7555 ( 11 ) keV [ T 1 / 2 = ( 5 + 3 − 2 ) ms ] for an isomeric state were identified in 195 Rn . In addition, the half-life and α decay energy of 196 Rn were measure…

Study of exotic decay of Cs isotope close to the proton drip line

6 pags., 6 figs. -- 27th International Nuclear Physics Conference (INPC2019) 29 July - 2 August 2019, Glasgow, UK

Multiparticle configurations of excited states in Lu155

Excited states in the neutron-deficient N = 84 nuclide Lu-155 have been populated by using the Pd-102(Ni-58, alpha p) reaction. The Lu-155 nuclei were separated by using the gas-filled recoil ion t ...

High-spin states beyond the proton drip-line: Quasiparticle alignments in Cs-113

Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to tentative spins of 45/2 and 51/2 h¯, with excitation energies over 8 MeV above the lowest state. These are the highest angular momenta and excitation energies observed to date in any nucleus beyond the proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study of aligned angular momenta, in comparison to the predictions of Woods–Saxon cranking calcu…

Production cross section and decay study of Es243 and Md249

In the study of the odd-$Z$, even-$N$ nuclei $^{243}$Es and $^{249}$Md, performed at the University of Jyv\"askyl\"a, the fusion-evaporation reactions $^{197}$Au($^{48}$Ca,2$n$)$^{243}$Es and $^{203}$Tl($^{48}$Ca,2$n$)$^{249}$Md have been used for the first time. Fusion-evaporation residues were selected and detected using the RITU gas-filled separator coupled with the focal-plane spectrometer GREAT. For $^{243}$Es, the recoil decay correlation analysis yielded a half-life of $24 \pm 3$s, and a maximum production cross section of $37 \pm 10$ nb. In the same way, a half-life of $26 \pm 1$ s, an $\alpha$ branching ratio of 75 $\pm$ 5%, and a maximum production cross section of 300 $\pm$ 80 nb…

Shapes and Collectivity in Neutron Deficient Even-Mass 188–198Pb Isotopes

Spectroscopy at the two-proton drip line: Excited states in 158W

Abstract Excited states have been identified in the heaviest known even-Z N = 84 isotone 158W, which lies in a region of one-proton emitters and the two-proton drip line. The observation of γ-ray transitions feeding the ground state establishes the excitation energy of the yrast 6+ state confirming the spin-gap nature of the α-decaying 8+ isomer. The 8+ isomer is also expected to be unbound to two-proton emission but no evidence for this decay mode was observed. An upper limit for the two-proton decay branch has been deduced as b 2 p ≤ 0.17% at the 90% confidence level. The possibility of observing two-proton emission from multiparticle isomers in nearby nuclides is considered.

High-spin states beyond the proton drip-line: Quasiparticle alignments in 113 Cs

Abstract Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to tentative spins of 45/2 and 51 / 2 ħ , with excitation energies over 8 MeV above the lowest state. These are the highest angular momenta and excitation energies observed to date in any nucleus beyond the proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study of aligned angular momenta, in comparison to the predictions of Woods–Saxon cra…

Detailed spectroscopy of 193Bi

An experiment aiming to study shape coexistence in 193Bi has been performed. Due to its transitional character, it has an exceptionally large number of structures identified close to the yrast line. Many new states have been found, significantly extending the previously known level scheme of 193Bi, including several new rotational bands. The π i13/2 band was extended to I π = 45/2+. The I π = 31/2+ member of the π i13/2 band was found to de-excite also to a long-lived isomeric state. This isomeric state is located at 2350 keV and has a spin and parity of 29/2+. The half-life of the isomeric state was measured to be 85(3) μs and it decays via the emission of an 84 keV E2 transition. A level …

Identification of a 6.6μs isomeric state in Ir175

Coulomb shifts and shape changes in the mass 70 region

The technique of recoil beta tagging has been developed which allows prompt gamma decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived beta decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in 78Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in 74Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in 70Br/70Se, 74Rb/74Kr, and 78Y/78Sr. The A=70 CED exhibit an anomalous behavior which is inco…

Spectroscopy of 193Bi

Shapes and Collectivity in Neutron Deficient Even-Mass 188–198Pb Isotopes

The neutron deficient 188−198Pb isotopes have been studied in a Coulomb excitation measurement employing the Miniball spectrometer and radioactive beams from REX-ISOLDE, CERN. These isotopes are of particular importance as they lie in a transitional region, where the intruding structures, associated with different deformed shapes, come down in energy close to the spherical ground state. For detailed analysis of the Coulomb excitation data, the understanding of the beam composition is essential. peerReviewed

Bandcrossings in 171Os

The nucleus Os-171 has been populated using the reaction Sn-116(Ni-58,2pn). Four new bands are identified, and the previously known bands are extended in spin, to a maximum of 53/2 (h) over bar. On ...

Gamma-ray and decay spectroscopy of 194,195,196At

Excited states of 195At have been studied by means of in-beam γ -ray spectroscopy and the recoil-decay tagging technique. A strongly coupled rotational band feeding the α-decaying 7/2− state via unobserved transitions was identified. This band is presumably built on the oblate proton I π = 13/2+ state. Confirming earlier measurements, α decays from the 1/2+ and 7/2− states were observed. Additionally, an E3 branch competing with the α decay of the 7/2− state was inferred. Also α decays of the odd-odd isotopes 194,196At were examined. peerReviewed

Collectivity in ${}^{\mathrm{196,198}}$Pb isotopes probed in Coulomb-excitation experiments at REX-ISOLDE

The neutron-deficient ${}^{\mathrm{196,198}}$Pb isotopes have been studied in Coulomb-excitation experiments employing the Miniball γ-ray spectrometer and radioactive ion beams from the REX-ISOLDE post-accelerator at CERN. The reduced transition probabilities of the first excited 2+ states in 196Pb and 198Pb nuclei have been measured for the first time. Values of $B(E2)={18.2}_{-4.1}^{+4.8}$ W.u. and $B(E2)={13.1}_{-3.5}^{+4.9}$ W.u., were obtained, respectively. The experiment sheds light on the development of collectivity when moving from the regime governed by the generalised seniority scheme to a region, where intruding structures, associated with different deformed shapes, start to com…

Collective rotation of an oblate nucleus at very high spin

International audience; A sequence of nine almost equidistant quadrupole transitions is observed in Nd137. The sequence represents an extremely regular rotational band that extends to a spin of about 75/2 and an excitation energy of ≈4.5MeV above yrast. Cranked mean-field calculations of the Nilsson-Strutinsky type suggest an oblate shape for the band. They reproduce the observed I(I+1) dependence of the rotational energy whereas predicting a pronounced decrease in the deformation, which is the hallmark of antimagnetic rotation.

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of Hg-182, Hg-184, Hg-186 and Hg-188

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate…

Determination of absolute internal conversion coefficients using the SAGE spectrometer

Abstract A non-reference based method to determine internal conversion coefficients using the SAGE spectrometer is carried out for transitions in the nuclei of 154 Sm, 152 Sm and 166 Yb. The Normalised-Peak-to-Gamma method is in general an efficient tool to extract internal conversion coefficients. However, in many cases the required well-known reference transitions are not available. The data analysis steps required to determine absolute internal conversion coefficients with the SAGE spectrometer are presented. In addition, several background suppression methods are introduced and an example of how ancillary detectors can be used to select specific reaction products is given. The results o…

Shape evolution in even-even N≤126, Z≥82 nuclei

The shape evolution in the neutron-de cient lead, polonium and radium nuclei has been investigated via in-beam and delayed y-ray and conversion electron spectroscopy. The lead isotope 180Pb is found to still exhibit prolate excited structure, related to the known intruder structures in the heavier isotopes. The production cross-section of 180Pb was only 10 nb, one of the lowest ever employed in an in-beam experiment. A candidate for an excited prolate band was found in 192Po, making it the rst polonium isotope for which both oblate and prolate rotational bands have been established. Contrary to the previous results, the current experiments indicate that the onset of deformation in the radiu…

Recoil-beta tagging study of the N=Z nucleus 66As

An in-beam study has been performed to further investigate the known isomeric decays and to identify T = 1 excited states in the medium-heavy N = Z = 33 nucleus 66As. The fusion-evaporation reaction 40Ca(28Si,pn) 66As was employed at beam energies of 75 and 83 MeV. The half-lives and ordering of two known isomeric states in 66As have been determined with improved accuracy. In addition, several prompt γ -ray transitions from excited states, both bypassing and decaying to the isomeric states in 66As, have been observed. Most importantly, candidates for the 4+ → 2+ and 6+ → 4+ transitions in the T = 1 band have been identified. The results are compared with shell-model calculations using the m…

Evolution from γ-soft to stable triaxiality in 136Nd as a prerequisite of chirality

The level structure of 136Nd has been investigated using the 100Mo(40Ar, 4n) reaction and the JUROGAM II+RITU+GREAT setup. The level scheme has been extended significantly. Many new bands have been identified both at low and high spin, among which are five nearly degenerate bands interpreted as chiral partners. Excitation energies, spins, and parities of the previously known bands are revised and firmly established, and some previously known bands have been revised. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. The band structure of 136Nd is now clarified and the various types of single-particle and collective excitations are well unders…

Low-lying electromagnetic transition strengths in 180 Pt

Lifetime measurements have been performed using the 98 Mo ( 86 Kr , 4 n ) 180 Pt reaction at a beam energy of 380 MeV, and the recoil distance Doppler-shift method. In a second experiment the 168 Yb ( 16 O , 4 n ) 180 Pt reaction at a beam energy of 88 MeV using the Ge-gated γ − γ fast timing technique was used to determine lifetimes. Lifetimes of the four lowest yrast states of 180 Pt have been determined. The experimental data are compared to calculations within the framework of the interacting boson model and the general collective model. Both models predict a deformed ground state and are consistent with all the remaining experimental results. peerReviewed

In-beam γ-ray spectroscopy of 190Po: First observation of a low-lying prolate band in Po isotopes

Gamma rays from excited states of 190Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones 188Pb and 186Hg. This indicates that in 190Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and potential energy surface calculations.

TPEN: A Triple-foil differential Plunger for lifetime measurements of excited states in Exotic Nuclei

Abstract A Triple-foil differential Plunger for Exotic Nuclei (TPEN) has been developed to measure the lifetimes of excited states in nuclei with small production cross-sections. TPEN utilises one target foil and two degrader foils to make differential lifetime measurements: directly determining the decay function and its derivative at a single plunger distance setting. The direct measurement of the decay function and its derivative removes the requirement to measure γ -ray intensities at several target-to-degrader distances, thereby reducing the beam-time required relative to a conventional plunger with a single-degrader foil. This paper describes the commissioning of TPEN in the lifetime …

First β -decay spectroscopy of In135 and new β -decay branches of In134

Fine structure in the α decay of Lu156 and Ta158

First observation of gamma-rays from the proton emitter 171Au

Gamma-rays from the alpha- and proton-unstable nuclide 171Au have been observed for the first time. The gamma-rays were correlated with both a proton- and an alpha-particle decay branch, confirming that the nucleus decays by alpha and proton emission from a single (11/2-) state. The measurement confirms the previously determined half-lives for these particle decays but the present values are of higher precision. In addition, a longer half-life than determined in previous work was measured for the proton-unstable tentative ground state. The results are discussed in relation to structures in neighbouring nuclei and compared with a Strutinsky-type TRS calculation.

The SPEDE spectrometer

8 pags., 10 figs., 2 tabs.

First observation of excited states in $^{197}$At: the onset of deformation in neutron-deficient astatine nuclei

Excited states in the Z= 85 nucleus 197At have been identified for the first time using the recoil-decay-tagging (RDT) technique. The excitation energy of these states is found to be consistent with the systematics of neutron-deficient astatine nuclei and with theoretical calculations indicating that the nucleus may be deformed in its ground state.

The SPEDE Spectrometer: Combined In-Beam γ-ray and Conversion Electron Spectroscopy with Radioactive Ion Beams

The SPEDE spectrometer [1] aims to combine a silicon detector, for the detection of electrons, with the MINIBALL γ-ray detection array for in-beam studies employing radioactive ion beams at the HIE-ISOLDE facility at CERN. The setup will be primarily used for octupole collectivity [2] and shape coexistence studies [3, 4] in Coulomb excitation experiments. In the shape coexistence cases the transitions between states of the same spin and parity have enhanced E0 strength [5]. Additionally the 0→0 transitions, typically present in nuclei exhibiting shape coexistence [6], can only occur via E0 transitions, i.e. via internal conversion electron emission.

Spin-dependent evolution of collectivity in 112Te

The evolution of collectivity with spin along the yrast line in the neutron-deficient nucleus 112Te has been studied by measuring the reduced transition probability of excited states in the yrast band. In particular, the lifetimes of the 4+ and 6+ excited states have been determined by using the recoil distance Doppler-shift method. The results are discussed using both large-scale shell-model and total Routhian surface calculations. peerReviewed

Detailed spectroscopy of 195Bi

An experiment focused on the study of shape coexistence and new high-spin structures in 195 Bi has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the 13 / 2 + isomeric state was extended up to I π = ( 49 / 2 + ) and an energy of 5706 keV. The I π = 31 / 2 + member of the π i 13 / 2 band was also found to feed a new long-lived isomeric state with an excitation energy of 2616 keV and a spin and parity of I π = 29 / 2 + . The half-life …

Lifetime measurements of excited states in Pt 172 and the variation of quadrupole transition strength with angular momentum

Lifetimes of the first excited 2þ and 4þ states in the extremely neutron-deficient nuclide 172Pt have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ ¼ 0.55ð19Þ was found, similar to a handful of other such anomalous cases observed in the entire Segr´e chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N ≈ 90–94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ rati…

First observation of excited states of 173Hg

The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of the decay of excited states via γ radiation are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighboring neutron-deficient Hg nuclei. In addition to the γ -ray spectroscopy, the α decay of this nucleus has been measured yielding superior precision to earlier measurements. peerReviewed

Lessons learned with the SAGE spectrometer

The SAGE spectrometer combines a high-efficiency γ-ray detection system with an electron spectrometer. Some of the design features have been known to be problematic and surprises have come up during the early implementation of the spectrometer. Tests related to bismuth germanate Compton-suppression shields, electron detection efficiency and an improved cooling system are discussed in the paper.

First identification of rotational band structures inRe9175166

Despite that it is more than 100 years since the atomic nucleus was first dis- covered by Ernest Rutherford and coworkers, many of its features still elude our understanding. The fact that the fundamental interactions between the nuclear constituents; nucleons, and ultimately quarks, are not yet known in detail, and the complexity of the nuclear many-body system compound the great challenges facing theoretical interpretations of experimental data. It is therefore important to focus on distinct phenomena where experimental mea- surements can be compared with theoretical predictions, providing stringent tests of theory. One such area is the nuclear phenomenology of collective excitations rela…

Population of a low-spin positive-parity band from high-spin intruder states in 177Au: The two-state mixing effect

The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam ?-ray spectroscopy. Specific tagging techniques, ?-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state. © 2020

Lifetime measurement in 195Po

The lifetime of the 17/2+ yrast state in 195Po has been measured using the recoil distance Doppler-shift technique to be $ \tau$ = 43(11) ps. The lifetime was extracted from the singles $ \gamma$ -ray spectra obtained by using the recoil-decay tagging method. The present work provides more information of the coupling schemes, shapes and configuration mixing in neutron-deficient odd-mass Po nuclei.

Low-lying excited states in the neutron-deficient isotopes 163Os and 165Os

Excited states in the neutron-deficient isotopes 163Os and 165Os were identified using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. The 163Os and 165Os nuclei were populated via the 106Cd(60Ni,3n) and 92Mo(78Kr,2p3n) reactions at bombarding energies of 270 MeV and 357 MeV, respectively. Gamma-ray emissions from these nuclei have been established unambiguously using the recoil-decay tagging technique and a coincidence analysis has allowed level schemes to be established. These results suggest that the yrast states are based upon negative-parity configurations originating from the νf7/2 and νh9/2 orbitals. peerReviewed

High-spin states of $^{218}$Th

Abstract High-spin states in the N = 128 nucleus 218Th have been investigated following fusion–evaporation reactions, using the recoil-decay tagging technique. Due to the short-lived nature of the ground state of 218Th prompt γ rays have been correlated with the α decay of the daughter nucleus 214Ra. The level scheme representing the decay of excited states has been extended to (16+) with the observation of six previously unreported transitions. The observations are compared with the results of shell model calculations and within the context of the systematics of neighbouring nuclei.

Isomer-tagged differential-plunger measurements in 113Xe

The 278-keV M2 γ decay from the νh11/2 isomeric state in 113Xe has been observed for the first time using the recoil-isomer tagging technique. The half-life of the isomer has been measured to be 6.9(3) μs. The derived B(M2) value is in agreement with the trend of systematic measurements of M2 transition strengths in neutron-deficient tellurium and tin isotopes. The lifetime of the first excited state in the νh11/2 band has been measured using the recoil distance Doppler-shift method. The extracted B(E2) value has been compared to theoretical CD-Bonn calculations and recent lifetime measurements in 109Te. This comparison of B(E2) values has been used to shed light on the possible influence o…

A simple timestamping data acquisition system for ToF-ERDA

A new data acquisition system, ToF-DAQ, has been developed for a ToF-ERDA telescope and other ToF-E and ToF-ToF measurement systems. ToF-DAQ combines an analogue electronics front-end to asynchronous time stamped data acquisition by means of a FPGA device. Coincidences are sought solely in software based on the timestamps. Timestamping offers more options for data analysis as coincidence events can be built also in offline analysis. The system utilises a National Instruments R-series FPGA device and a Windows PC as a host computer. Both the FPGA code and the host software were developed using the National Instruments LabVIEW graphical programming environment. Up to eight NIM ADCs can be han…

In-beam γ-ray spectroscopy of low- and medium-spin levels in 211Po

The structure of the low- and medium-spin levels of the 211Po nucleus have been studied with in-beam γ-ray spectroscopy with the 208Pb(α,n)211Po fusion-evaporation reaction. The level scheme was further extended with levels of the configurations π(h9/2)22+−4+⊗νg9/2, π(h9/2)28+⊗νg9/2, π(h9/2)22+−4+⊗νi11/2, π(h9/2)22+−4+⊗νj15/2, π(h9/2f7/2)8+⊗νg9/2, and π(h9/2)20+⊗ν(g9/2)20+(s1/2)−1. The single-particle neutron states νd5/2 and νs1/2 were also identified. Furthermore, a number of states feeding the low-spin structures were added. peerReviewed

Characterizing the atomic mass surface beyond the proton drip line via {\alpha}-decay measurements of the {\pi}s1/2 ground state of 165Re and the {\pi}h11/2 isomer in 161Ta

The α-decay chains originating from the πs1/2 and πh11/2 states in 173Au have been investigated following fusion-evaporation reactions. Four generations of α radioactivities have been correlated with 173Aum leading to a measurement of the α decay of 161Tam. It has been found that the known α decay of 161Ta, which was previously associated with the decay of the ground state, is in fact the decay of an isomeric state. This work also reports on the first observation of prompt γ rays feeding the ground state of 173Au. This prompt γ radiation was used to aid the study of the α-decay chain originating from the πs1/2 state in 173Au. Three generations of α decays have been correlated with this stat…

Transmission Efficiency of the SAGE Spectrometer Using GEANT4

The new SAGE spectrometer allows simultaneous electron and γ-ray in-beam studies of heavy nuclei. A comprehensive GEANT4 simulation suite has been created for the SAGE spectrometer. This includes both the silicon detectors for electron detection and the germanium detectors for γ-ray detection. The simulation can be used for a wide variety of tests with the aim of better understanding the behaviour of SAGE. A number of aspects of electron transmission are presented here.

Competing single-particle and collective states in the low-energy structure of 113I

To understand the low-energy structure of the neutron deficient iodine isotopes, lifetimes for the low-lying 9/2+ and 11/2+ positive-parity states in 113I have been measured as τ = 28(4) ps and τ = 3.7(7) ps, respectively. The lifetime for the 11/2− state, which feeds the 9/2+ and 11/2+ states, was remeasured with improved accuracy as τ = 216(7) ps. The reduced transition probability, B(E2) = 32(5) W.u., for the 9/2+ → 5/2+ transition agrees with that calculated within the shell model using a Hamiltonian based on the charge-dependent Bonn nucleon-nucleon interaction. In contrast, the much larger transition probability, B(E2) = 209(39) W.u., measured for the 11/2+ → 7/2+ transition has been …

Deformation of the proton emitterCs113from electromagnetic transition and proton-emission rates

The lifetime of the $(11/{2}^{+})$ state in the band above the proton-emitting $(3/{2}^{+})$ state in $^{113}\mathrm{Cs}$ has been measured to be $\ensuremath{\tau}=24(6)$ ps from a recoil-decay-tagged differential-plunger experiment. The measured lifetime was used to deduce the deformation of the states using wave functions from a nonadiabatic quasiparticle model to independently calculate both proton-emission and electromagnetic $\ensuremath{\gamma}$-ray transition rates as a function of deformation. The only quadrupole deformation, which was able to reproduce the experimental excitation energies of the states, the electromagnetic decay rate of the $(11/{2}^{+})$ state and the proton-emis…

Lifetime measurements of excited states in W162 and W164 and the evolution of collectivity in rare-earth nuclei

Lifetimes of the first excited 2(+) states in the extremely neutron- deficient W-162 and W-164 nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data f ...

Spectroscopy of proton-rich 66^Se up to J^�� = 6^+: isospin-breaking effect in the A = 66 isobaric triplet

Candidates for three excited states in the 66^Se have been identified using the recoil-�� tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analogue states across the A = 66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f_7/2 shell. Shell-model calculations indicate a continued need for an additional isospin non-conserving interaction in addition to the Coulomb isotensor part as a function of mass.

Spectroscopy of At 201 including the observation of a shears band and the 29/2 + isomeric state

The excited states of 201At were studied and an isomeric 29/2 + state [T1/2 = 3.39(9) μs] was identified by using a fusion-evaporation reaction, a gas-filled recoil separator, and recoil gating techniques. The 29/2 + state is suggested to originate from the π(h9/2) ⊗ |200Po;11− configuration, and it decays through the 269- and 339-keV E2- and E3-type transitions, respectively. Moreover, a cascade of magnetic dipole transitions that is suggested to originate from a shears band was observed by using recoil-gated γ − γ (−γ ) coincidence techniques. peerReviewed

Study of Intermediate-spin States of $^{98}$Y

The nuclear structure of the odd–odd nucleus 98Y has been re-investigated by observing prompt γ rays emitted following the proton-induced fission of a 238U target, using the JUROGAM-II multidetector array. New highspin decays have been observed and placed in the level schemes using triple coincidences. The experimental level energies and γ-decay patterns are compared to GICM and QPRM calculations, assuming that this neutronrich N = 59 isotone is spherical at low energies and prolate deformed at intermediate spins. Web of Science 47 3 916 911

Collective excitations in the transitional nuclei 163Re and 165Re

Excited states in the neutron-deficient nuclei 163 75 Re88 and 165 75 Re90 were populated in the 106Cd(60Ni, p2nγ ) and 92Mo(78Kr, 3p2nγ ) fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. γ rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for 163Re and 165Re were identified using recoil-decay correlation techniques. At low spin, the yrast bands of these isotopes consist of signature partner bands based on a single πh11/2 quasiproton configuration. The bands display large energy spl…