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…

First Accurate Normalization of the $\beta$-delayed $\alpha$ Decay of $^{16}$N and Implications for the $^{12}$C$(\alpha,\gamma)^{16}$O Astrophysical Reaction Rate

The $^{12}\text{C}(\alpha,\gamma){}^{16}\text{O}$ reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced $\alpha$ width, $\gamma_{11}$, of the bound $1^-$ level in $^{16}$O is particularly important to determine the cross section. The magnitude of $\gamma_{11}$ is determined via sub-Coulomb $\alpha$-transfer reactions or the $\beta$-delayed $\alpha$ decay of $^{16}$N, but the latter approach is presently hampered by the lack of sufficiently precise data on the $\beta$-decay branching ratios. Here we report improved branching ratios for the bound $1^-$ level [$b_{\beta…

Spectroscopy of nuclei approaching the proton drip-line using a secondary-fragmentation technique with the RISING detector array

An experiment utilizing a double fragmentation reaction was performed to study isobaric analogue states in A similar to 50 nuclei approaching the proton drip-line. gamma-ray spectroscopy will be used to identify excited states in the neutron-deficient nuclei produced in the second fragmentation reaction. Excited state level schemes will be obtained, through comparison with states in their well-known mirror partners, along with information on Coulomb effects through measurements of the Coulomb energy differences between isobaric analogue excited states. The validity of isospin symmetry for nuclei approaching the proton drip-line can also be investigated and the information gained will aid in…

New ß-decaying state in 214Bi

Role of the Δ Resonance in the Population of a Four-Nucleon State in the Fe56→Fe54 Reaction at Relativistic Energies

The 54Fe nucleus was populated from a 56Fe beam impinging on a Be target with an energy of E=A ¼ 500 MeV. The internal decay via γ-ray emission of the 10þ metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the 56Fe ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of 54Fe, suggesting that it was populated via the decay of the Δ0 resonance into a proton. This process allows the population of fournucleon states, such as the observed isomer. Therefore, it is concluded that the obser…

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…

Decays of new nuclides and isomers beyond the proton drip line - The influence of neutron configurations

Bozok University;Erciyes University;et al.;Istanbul University;Nigde University;The Turkish Atomic Energy Authority (TAEK)

Decay studies of the long-lived states in $^{186}$Tl

Decay spectroscopy of the long-lived states in $^{186}$Tl has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The $\alpha$ decay from the low-spin $(2^-)$ state in $^{186}$Tl was observed for the first time and a half-life of $3.4^{+0.5}_{-0.4}$ s was determined. Based on the $\alpha$-decay energy, the relative positions of the long-lived states were fixed, with the $(2^-)$ state as the ground state, the $7^{(+)}$ state at 77(56)~keV and the $10^{(-)}$ state at 451(56) keV. The level scheme of the internal decay of the $^{186}$Tl($10^{(-)}$) state ($T_{1/2} = 3.40(9)$ s), which was known to decay solely through emission of 374 keV $\gamma$-ray transition, was extended and a lowe…

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

First observation of excited states inHg17595

Excited states of the neutron-deficient nucleus Hg-175, populated using fusion-evaporation reactions, are reported for the first time. The spin and parity of the ground state has been determined to ...

Decay studies of the long-lived states in Tl-186

9 pags., 12 figs., 3 tabs.

Lifetime measurements in neutron-rich63,65Co isotopes using the AGATA demonstrator

Lifetimes of the low-lying (11/2-) states in 63,65Co have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA γ-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a 238U target with a beam of 64Ni. The experimental B(E2) reduced transition probabilities for 63,65Co are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N=40 67Co isotope

Octupole states in Tl207 studied through β decay

The β decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through γ-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the πs−11/2, πd−13/2, and πh−111/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with st…

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…

Lifetime measurement of neutron-rich even-even molybdenum isotopes

D. Ralet et al. -- 11 pags., 10 figs., 3 tabs.

Lifetime measurements in Ti52,54 to study shell evolution toward N=32

Lifetimes of the excited states in the neutron-rich Ti-52,Ti-54 nuclei, produced in a multinucleon-transfer reaction, were measured by employing the Cologne plunger device and the recoil-distance D ...

Quasiparticle alignments andα-decay fine structure of175Pt

Excited states and decay properties of ${}^{175}$Pt have been investigated using the ${}^{92}$Mo${(}^{86}\mathrm{Sr},2pn)$ fusion-evaporation reaction. The JUROGAM I $\ensuremath{\gamma}$-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 ${I}^{\ensuremath{\pi}}=({{}^{7}{/}_{2}}^{\ensuremath{-}})$ ground state in ${}^{175}$Pt, have been established and the known yrast band has been extended up to ${I}^{\ensuremath{\pi}}=({{}^{49}{/}_{2}}^{+})$. Rotational properties of the excited states i…

Pygmy dipole resonance in 124Sn populated by inelastic scattering of 17O

L. Pellegri et al. ; 5 pags. ; 6 figs. ; open access article under the CC BY license. Funded by SCOAP3

Competition between allowed and first-forbidden β decays of At208 and expansion of the Po208 level scheme

The structure of 208Po populated through the EC/β+ decay of 208At is investigated using γ-ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed γ rays which have been (re)assigned a position. The level scheme is compared to shell model calculations. Through this analysis approximately half of the β-decay strength of 208At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations. This mass r…

Precision measurements of proton emission from the ground states of 156Ta and 160Re

The decays of the πd3/2 ground states of 156Ta and 160Re have been studied in detail using the GREAT spectrometer. More than 7000 160Re nuclei were produced in reactions of 290- and 300-MeV 58Ni ions with an isotopically enriched 106Cd target and separated in flight using the RITU separator. The proton and α decays of the πd3/2 level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be t1/2=611±7 μs and bp=89±1% and bα=11±1%, respectively. The α-decay branch populated the ground state of 156Ta, allowing improved values for the proton-decay energy and half-life to be obtained (Ep=1011±5 keV; t1/2=106±4 ms). The β decay of this leve…

Decay of the high-spin isomer in 160Re: Changing single-particle structure beyond the proton drip line

WOS: 000286708700015

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…

First ß-decay spectroscopy of 135In and new ß-decay branches of 134In

Decay studies of the long-lived states in Tl186

Decay spectroscopy of the long-lived states in 186Tl has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The α decay from the low-spin (2−) state in 186Tl was observed for the first time and a half-life of 3.4+0.5−0.4 s was determined. Based on the α-decay energy, the relative positions of the long-lived states were fixed, with the (2−) state as the ground state, the 7(+) state at 77(56) keV, and the 10(−) state at 451(56) keV. The level scheme of the internal decay of the 186Tl(10(−)) state [T1/2=3.40(9) s], which was known to decay solely through emission of 374-keV γ-ray transition, was extended and a lower limit for the β-decay branching bβ>5.9(3)% was determined. The extrac…

Compton imaging with AGATA and SmartPET for DESPEC

DESPEC (DEcay SPECtroscopy) is a spectrometer, currently under construction, which is to be used at the FAIR (Facility for Antiproton and Ion Research) facility at GSI Darmstadt, Germany, as part of the NuSTAR (Nuclear STructure, Astrophysics and Reactions) project. Its goal is to analyse the decay of exotic nuclei produced via the Super-FRS (SUPERconducting FRagment Separator). The optimal configuration of certain elements of the spectrometer, namely a HPGe (High Purity Germanium) tracking array, is still under consideration. Work currently being carried out at the University of Liverpool using a segmented, coaxial HPGe detector (AGATA B009) and a pixelated, planar HPGe detector (SmartPET …

Beta-delayed neutron spectroscopy of $^{133}$In

The decay properties of In133 were studied in detail at the ISOLDE Decay Station. The implementation of the Resonance Ionization Laser Ion Source allowed separate measurements of its 9/2+ ground state (In133g) and 1/2− isomer (In133m). With the use of β-delayed neutron and γ spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition 9/2+→7/2+ was located at 5.93 MeV in the In133g decay with a logft=4.7(1). In addition, several neutron-unbound states were populated at lower excitation energies by the first-forbidden decays of In133g,m. We assigned spins and parities to those neutro…

First β -decay spectroscopy of In 135 and new β -decay branches of In 134

First Accurate Normalization of the β-delayed α Decay of ^{16}N and Implications for the ^{12}C(α,γ)^{16}O Astrophysical Reaction Rate.

The ^{12}C(α,γ)^{16}O reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ_{11}, of the bound 1^{-} level in ^{16}O is particularly important to determine the cross section. The magnitude of γ_{11} is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of ^{16}N, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1^{-} level [b_{β,11}=(5.02±0.10)×10^{-2}] and for β-delayed α emission [b_{βα}=(1.59±0.06)×10^{-5}].…

First Accurate Normalization of the β -delayed α Decay of N16 and Implications for the C12(α,γ)O16 Astrophysical Reaction Rate

The C-12(alpha,gamma)O-16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced a width, gamma(11), of the bound 1(-) level in O-16 is particularly important to determine the cross section. The magnitude of gamma(11) is determined via sub-Coulomb a-transfer reactions or the beta-delayed a decay of N-16, but the latter approach is presently hampered by the lack of sufficiently precise data on the beta-decay branching ratios. Here we report improved branching ratios for the bound 1(-) level [b(beta,11) = (5.02 +/- 0.10) x 10(-2)] and for beta-delayed alpha emission [b(…

Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in 106,108Sn

The lifetimes of the low-lying excited states 2(+) and 4(+) have been directly measured in the neutron-deficient Sn-106,Sn-108 isotopes. the nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. the emitted gamma rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2; 2(1)(+) -> 0(g.s)(+)) values and it describes well the experimental pattern for Sn104-114 ; the B…

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

Competition between Allowed and First-Forbidden β Decay: The Case of Hg208→Tl208

The β decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Q_{β} window, only three negative parity states are populated directly in the β decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in…

Detailed spectroscopy of doubly magic $^{132}$Sn

The structure of the doubly magic $^{132}_{50}$Sn$_{82}$ has been investigated at the ISOLDE facility at CERN, populated both by the $\beta^-$decay of $^{132}$In and $\beta^-$-delayed neutron emission of $^{133}$In. The level scheme of $^{132}$Sn is greatly expanded with the addition of 68 $\gamma$-transitions and 17 levels observed for the first time in the $\beta$ decay. The information on the excited structure is completed by new $\gamma$-transitions and states populated in the $\beta$-n decay of $^{133}$In. Improved delayed neutron emission probabilities are obtained both for $^{132}$In and $^{133}$In. Level lifetimes are measured via the Advanced Time-Delayed $\beta\gamma\gamma$(t) fas…

Spectroscopy of the neutron-deficient nucleusOs16791

Excited states of the nucleus Os-167 have been populated by the reaction Mo-92(Kr-78,2pn). The JUROGAM gamma-ray detector array has been used in conjunction with the RITU gas-filled separator and the GREAT spectrometer to observe prompt gamma rays in coincidence with recoiling fusion-evaporation residues and their subsequent decay by alpha particle emission. By correlating prompt gamma radiation with the characteristic alpha radioactivity of Os-167, it has been possible to extend the level scheme for this nucleus significantly. In particular, an extension of the yrast band and four previously unobserved bands are reported. In addition, the recoil distance Doppler-shift method was used to de…

Precision measurements of proton emission from the ground states ofTa156andRe160

The decays of the $\ensuremath{\pi}{d}_{3/2}$ ground states of $^{156}\mathrm{Ta}$ and $^{160}\mathrm{Re}$ have been studied in detail using the GREAT spectrometer. More than 7000 $^{160}\mathrm{Re}$ nuclei were produced in reactions of 290- and 300-MeV $^{58}\mathrm{Ni}$ ions with an isotopically enriched $^{106}\mathrm{Cd}$ target and separated in flight using the RITU separator. The proton and $\ensuremath{\alpha}$ decays of the $\ensuremath{\pi}{d}_{3/2}$ level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be ${t}_{1/2}=611\ifmmode\pm\else\textpm\fi{}7$ $\ensuremath{\mu}$s and ${b}_{\mathrm{p}}=89\ifmmode\pm\else\textpm\fi…

β decay of In133 : γ emission from neutron-unbound states in Sn133

Excited states in Sn-133 were investigated through the beta decay of In-133 at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for In-133, allowing us to study separately, and in detail, the beta-decay branch of In-133 J(pi)= (9/2(+)) ground state and its J(pi) = (1/2(-)) isomer.Thanks to the large spin difference of the two beta-decaying states of In-133, it is possible to investigate separately the lower and higher spin states in the daughter, Sn-133, and thus to probe independently different single-particle and single-hole levels. We report here new gamma transitions observed in the decay of In-133, including those assign…

Spectroscopy along Flerovium Decay Chains: Discovery ofDs280and an Excited State inCn282

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made eleme…

Evidence of Partial Seniority Conservation in the pi g9/2 Shell for the N=50 Isotones

The reduced transition probabilities for the 4-&gt; and 2-&gt;0 transitions in 92Mo and 94Ru and for the 4-&gt;2 and 6-&gt;4 transitions in 90Zr have been determined in this experiment making use of a multinucleon transfer reaction. These results have been interpreted on the basis of realistic shell-model calculations in the f5/2, p3/2, p1/2, and g9/2 proton valence space. Only the combination of extensive lifetime information and large scale shell-model calculations allowed the extent of the seniority conservation in the N=50 g9/2 orbital to be understood. The conclusion is that seniority is largely conserved in the first πg9/2 orbital.

Interaction position resolution simulations and in-beam measurements of the AGATA HPGe detectors

WOS: 000290082600015

Study of isomeric states in $^{198,200,202,206}$Pb and $^{206}$Hg populated in fragmentation reactions

International audience; Isomeric states in isotopes in the vicinity of doubly-magic 208Pb were populatedfollowing reactions of a relativistic 208Pb primary beam impinging on a9Be fragmentation target. Secondary beams of 198,200,202,206Pb and 206Hg wereisotopically separated and implanted in a passive stopper positioned in thefocal plane of the GSI Fragment Separator. Delayed γ rays were detected withthe Advanced Gamma Tracking Array (AGATA). Decay schemes were reevaluatedand interpreted with shell-model calculations. The momentumdependentpopulation of isomeric states in the two-nucleon hole nuclei206Pb/206Hg was found to differ from the population of multi neutron-holeisomeric states in 198…

AGATA-Advanced GAmma Tracking Array

WOS: 000300864200005