A new differentially pumped plunger device to measure excited-state lifetimes in proton emitting nuclei

Abstract A new plunger device has been designed and built to measure the lifetimes of unbound states in exotic nuclei beyond the proton drip-line. The device has been designed to work in both vacuum and dilute-gas environments made possible through the introduction of a low-voltage stepping motor. DPUNS will be used in conjunction with the gas-filled separator RITU and the vacuum separator MARA at the accelerator laboratory of the University of Jyvaskyla, Finland, to measure the lifetimes of excited states with low population cross-sections. This is achieved by eliminating the need for a carbon foil to isolate the helium gas of RITU from the beam line thus reducing the background from beam-…

Inner shell ionization of argon in ECRIS plasma

Abstract The volumetric K α emission rate of argon emitted from the electron cyclotron resonance (ECR) heated plasmas of the JYFL (University of Jyvaskyla, Department of Physics) 14 GHz ECR ion source (ECRIS) and the 14.5 GHz Grenoble Test Source (GTS) at iThemba Laboratory for Accelerator Based Sciences have been measured to gain an understanding of the influence of the ion source tune parameters on the absolute inner shell ionization rate. It was observed that the behaviour of the ionization rate and the extracted ion beam currents react differently, depending the parametric sweep performed. The neutral gas pressure and incident microwave power was found to have the strongest influence on…

Probing the shape of176Hgalong the yrast line

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

Shape isomerism and spectroscopy ofHg177

High spin states in the $^{177}\mathrm{Hg}$ nucleus were populated by the $^{144}\mathrm{Sm}(^{36}\mathrm{Ar},3\mathrm{n})^{177}\mathrm{Hg}$ reaction at a beam energy of $178\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The emitted prompt $\ensuremath{\gamma}$ rays were detected with the Jurosphere $\ensuremath{\gamma}$-ray spectrometer, while the recoiling nuclei were identified using an active stopper at the focal plane of the gas-filled separator RITU. A quasi-rotational band that decays to an isomeric state with a half-life ${t}_{1∕2}=1.50\ifmmode\pm\else\textpm\fi{}0.15\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ and its subsequent $\ensuremath{\gamma}$ decay to the ground state of…

Advanced time-stamped total data acquisition control front-end for MeV ion beam microscopy and proton beam writing

Many ion-matter interactions exhibit [email protected] time dependences such as, fluorophore emission quenching and ion beam induced charge (IBIC). Conventional event-mode MeV ion microbeam data acquisition systems discard the time information. Here we describe a fast time-stamping data acquisition front-end based on the concurrent processing capabilities of a Field Programmable Gate Array (FPGA). The system is intended for MeV ion microscopy and MeV ion beam lithography. The speed of the system (>240,000 events s^-^1 for four analogue to digital converters (ADC)) is limited by the ADC throughput and data handling speed of the host computer.

High-spin study of 119Xe

Abstract High-spin states have been populated in 54 119 Xe via the 96 Mo( 27 Al,p3n) reaction at 133 MeV, using the Jurosphere γ-ray spectrometer to record triple γ-ray coincidences. The known level scheme has been significantly extended and several band crossings identified. In particular, the νh 11 2 yrast band has been extended to I π = ( 83 2 − ) and shows features which are consistent with those of smooth band termination at high spin. Theoretical results for 119 Xe at high spin are discussed within the framework of cranked Nilsson-Strutinsky calculations, together with results for 117 Xe.

First observation of excited states in the neutron deficientN=86isotones159Taand160W

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.

In-beam and decay spectroscopy of very neutron deficient iridium nuclei

Iridium nuclei at and beyond the proton drip line have been studied via fusion evaporation reactions. A reaction of 92Mo(78Kr, p2n) at a beam energy of 360 MeV and target thickness 500 µg cm−2 was employed to study 167,167mIr. A reaction of 112Sn(58Ni, p2n) at a beam energy of 266 MeV and target thickness 500 µg cm−2 was used to study 169,169mIr. The experiments were performed at the University of Jyvaskyla utilizing the RITU separator in conjunction with the focal plane GREAT spectrometer and the JUROGAM Ge array at the target position. Excited states feeding both the ground state and isomeric state in 169Ir, excited states feeding the ground state of 167Ir and the ground state alpha decay…

Position resolution of the prototype AGATA triple-cluster detector from an in-beam experiment

AGATA belongs to a new generation of gamma-ray detector arrays for nuclear spectroscopy at present in its final stage of development. The detectors of these new arrays will be based on 36-fold electronically segmented coaxial germanium diodes operated in position sensitive mode. An in-beam test of the AGATA prototype triple cluster detector was carried out with the purpose of demonstrating the feasibility of such detectors and in order to measure the most sensitive parameters for their overall performance. An inverse kinematics reaction was performed, using a (48)Ti beam at an energy of 100MeV, impinging on a deuterated titanium tat-get. The results from the analysis of the experimental dat…

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.

Evolution of collectivity inHg180andHg182

Lifetimes of yrast states in $^{180}\mathrm{Hg}$ up to the ${8}^{+}$ state and of the ${9}^{\ensuremath{-}}$ state have been extracted from recoil-decay tagged $\ensuremath{\gamma}$-ray spectra by using the recoil distance Doppler-shift method. In addition, lifetimes of yrast states up to the ${10}^{+}$ state in $^{182}\mathrm{Hg}$ have been extracted from recoil-gated $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence spectra. The present study addresses the evolution of collectivity of two competing shapes in neutron-deficient Hg nuclei as a function of $A$ and the configuration mixing at low spin.

New developments on the recoil distance doppler-shift method

Absolute transition probabilities are fundamental observables for nuclear structure. The recoil-distance-Doppler-shift (RDDS) technique, also called plunger technique, is a well established tool for the determination of these important experimental quantities via the measurement of lifetimes of excited nuclear states. Nowadays nuclear structure investigations are concentrated on exotic nuclei which are often produced with extremely small cross sections or with very low beam intensities. In order to use the RDDS technique also for the investigation of very exotic nuclei this method has to be adapted to the specific needs of these special reactions. This article gives an overview on recent RD…

Investigation of E0 Transition in 74Kr

The N = Z+2 nucleus 74Kr has been investigated by in-beam conversion electron (CE) and γ ray spectroscopy. The electric-monopole (E0) decay was examined in order to confirm the evidence for a low-lying isomeric 0+2 state and to give insight into the mixing between the predicted coexisting prolate and oblate shapes.

In-beam spectroscopy of $^{253,254}$No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei 253,254No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyvaskyla. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of 253No are discussed.

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.

X(5) critical-point symmetries in 138Gd

International audience; The lifetimes of low-lying transitions in 138Gd have been measured using the recoil-distance Doppler-shift technique. The resultant reduced transition probabilities have been compared to X(5) critical-point calculations to assess the potential 'phase-transitional' behaviour of 138Gd. The X(5) symmetry describes the first order 'phase transition' between sphericity, U(5) and an axially deformed nuclear shape, SU(3). Although a high degree of correspondence is observed between the experimental and theoretical excitation energies, the large uncertainties of the experimental B(E2) values cannot preclude contributions from either vibrational or rotational modes of excitat…

Intruder states in even-even neutron-rich Pd isotopes

The decays of 112Rh g and 112Rh m obtained as on-line mass separated fission products have been investigated by standard β and γ spectroscopic techniques and γ-γ angular correlations. Low-lying 0+ and 2+ states are identified in the daughter nucleus 112Pd. Systematics suggests the existence of an intruder band which is the lowest in 110Pd, i.e. two neutrons before the midshell.

Experimental evidence on microwave induced electron losses from ECRIS plasma

The balance between warm and hot (>1 keV) electron density and their losses from the magnetic confinement system of an Electron Cyclotron Resonance Ion Source (ECRIS) plasma is considered to be one of the main factors determining the rate of the high charge state ion production. One of the key loss channels for heated electrons is thought to be induced by the injected microwaves. While this loss mechanism, referred to as rf-induced pitch angle scattering, has been studied theoretically and with computational tools, direct experimental evidence of its significance in minimum-B ECRIS plasmas remains limited. In this work, experimental evidence of microwave induced electron losses in the axial…

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.

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.

Recoil isomer tagging in the proton-rich odd-oddN=77isotones, 65142Tband 67144Ho

Reduced transition probabilities along the yrast line in W-166

WOS: 000406755100001

Isomer Spectroscopy in90216Th126and the Magicity of92218U126

Excited states in (216)Th were investigated via prompt and delayed gamma decays and the recoil-decay tagging method. The decay schemes of the I(pi) = (8+), t(1/2) = 128(8) micros, the I(pi) = (11-), t(1/2) = 615(55) ns, and the I(pi) = (14+), t(1/2) > or = 130 ns isomers were established. The configuration pi h(9/2)f(7/2) is assigned to the I(pi) = (8+) isomer, which implies that the h(9/2) and f(7/2) states are nearly degenerate. This is ascribed to increased binding of the f(7/2) orbital by its coupling to a low-lying I(pi) = (3-) state at E(x) = 1687 keV. The role of octupole and pairing correlations for a Z = 92 shell closure prediction is discussed on the basis of shell model calculati…

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.

Anomalous transition strength in the proton-unbound nucleus I5653109

A lifetime measurement has been made for the first excited 11/2(+) state in the proton-unbound nucleus (109)(53)I56 using the recoil-distance Doppler-shift method in conjunction with recoil-proton ...

Time Evolution of High-Energy Bremsstrahlung and Argon Ion Production in Electron Cyclotron Resonance Ion-Source Plasma

Bremsstrahlung radiation measurement is one of the most commonly used plasma-diagnostics methods. Most of the bremsstrahlung measurements with electron cyclotron resonance ion sources (ECRISs) have been performed in continuous-operation mode yielding information only on the steady-state bremsstrahlung emission. This paper describes results of bremsstrahlung and argon ion-current measurements with the JYFL 14-GHz ECRIS operated in a pulsed mode. The bremsstrahlung radiation was studied as a function of neutral-gas pressure and radio frequency power. The timescale of ECRIS bremsstrahlung production is compared to ion-production timescale for different charge states of argon for the first time…

In-beam spectroscopy using the JYFL gas-filled magnetic recoil separator RITU

The techniques of recoil-gating and recoil-decay tagging have been employed at Jyvaskyla to perform in-beam γ-ray and electron spectroscopy studies of heavy nuclei. The JUROSPHERE γ-ray array and the SACRED electron spectrometer have been placed at the target position of the JYFL gas-filled recoil separator recoil ion transport unit (RITU). The RITU separator has been used to collect the recoils of interest and separate them from beam particles and fission products. At the focal plane a detector system consisting of time-of-flight and implantation detectors has been used for further event identification. The method and some highlights from the results in the lead region close to the proton …

Promptγ-ray spectroscopy of the neutron-rich124Cd

Prompt γ -ray spectroscopy of neutron-rich cadmium isotopes has been performed. The nuclei of interest have been populated via a 25-MeV, proton-induced fission of the 238 U thick target and prompt γ -rays measured using the multi-detector HPGe array JUROGAM II. New high-spin decays have been observed and placed in the level scheme using triple coincidence gates. The experimental results are compared to shell-model calculations and show good agreement.

A new recoil distance technique using low energy coulomb excitation in inverse kinematics

Abstract We report on the first experiment combining the Recoil Distance Doppler Shift technique and multistep Coulomb excitation in inverse kinematics at beam energies of 3–10 A MeV. The setup involves a standard plunger device equipped with a degrader foil instead of the normally used stopper foil. An array of particle detectors is positioned at forward angles to detect target-like recoil nuclei which are used as a trigger to discriminate against excitations in the degrader foil. The method has been successfully applied to measure lifetimes in 128Xe and is suited to be a useful tool for experiments with radioactive ion beams.

First observation of excited states in 184Pb: spectroscopy beyond the neutron mid-shell

Excited states have been identified for the first time in 184Pb, the first even-even Pb isotope beyond the 82 < N < 126 mid-shell, using the recoil-decay tagging (RDT) technique. A collective band built on the first-excited 2+ state has been observed. This resembles those seen in 186,188Pb and the Hg isotones, and can thus be associated with a prolate-deformed shape. Variable moment of inertia (VMI) fits of the prolate 0+ level energies in 184,186,188Pb indicate that the minimum appears at N= 103, the same neutron number at which the corresponding minimum in Hg isotopes is observed.

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…

Fine structure in -decay and shape coexistence in

Excited states in populated in the -decay of have been identified through -particle-conversion electron coincidences. The level scheme has been interpreted using a configuration mixing calculation, providing estimates of the mixing matrix elements, mixing amplitudes and the energies of unperturbed and unobserved levels.

Shape coexistence at the proton drip-line: First identification of excited states inPb180

Excited states in the extremely neutron-deficient nucleus {sup 180}Pb have been identified for the first time using the JUROGAM II array in conjunction with the RITU recoil separator at the Accelerator Laboratory of the University of Jyvaeskylae. This study lies at the limit of what is presently achievable with in-beam spectroscopy, with an estimated cross section of only 10 nb for the {sup 92}Mo({sup 90}Zr,2n){sup 180}Pb reaction. A continuation of the trend observed in {sup 182}Pb and {sup 184}Pb is seen, where the prolate minimum continues to rise beyond the N=104 midshell with respect to the spherical ground state. Beyond-mean-field calculations are in reasonable correspondence with the…

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 …

New information on 12C states from the decays of 12N and 12B

Abstract The properties of states in 12 C above the 3α-threshold are of high current interest for nuclear astrophysics and for the nuclear many-body problem in general. We have initiated a series of experiments aimed at elucidating this region by using the β-decays of 12 N and 12 B. By applying the ISOL method for producing these radioactive isotopes, in combination with modern segmented charged particle detectors, our approach has significant advantages over previous studies of this region.

Recoil-beta tagging: A novel technique for studying proton-drip-line nuclei

Abstract Tagging with charged particles and γ -rays at the focal plane of recoil separators has proven, over the last two decades, to be a very powerful tool for the identification of excited states in exotic nuclei produced with very low cross-sections. One of the key areas so far unexplored in terms of the tagging methodology has been performing correlations with β -particles at the focal plane of a recoil separator. A new technique entitled Recoil-Beta Tagging (RBT) has been developed, this technique exploits the unusual properties of Fermi super-allowed β emitters, which have both a short half-life ( ∼ 100 ms ) and high β + -endpoint energy. Correlating with such β -particles using a do…

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…

The effect of magnetic field strength on the time evolution of high energy bremsstrahlung radiation created by an electron cyclotron resonance ion source

Abstract An electron cyclotron resonance (ECR) ion source is one of the most used ion source types for high charge state heavy ion production. In ECR plasma the electrons are heated by radio frequency microwaves in order to provide ionization of neutral gases. As a consequence, ECR heating also generates very high electron energies (up to MeV region) which can produce a vast amount of bremsstrahlung radiation causing problems with radiation shielding and heating superconducting cryostat of an ECR ion source. To gain information about the time evolution of the electron energies in ECR plasma radial bremsstrahlung measurements were performed. JYFL 14 GHz ECR ion source was operated in pulsed …

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…

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 ...

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 ...

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.

Structure of rotational bands in 253No

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.

Shape coexistence in odd-mass Au isotopes: Determination of the excitation energy of the lowest intruder state in ^{179}Au

Abstract Phenomenon of the shape coexistence has been investigated in 17979Au100. This very neutron-deficient isotope, 18 neutrons away from the stable gold isotope 19779Au118, was studied by a combination of α-decay and isomer-decay spectroscopy employing the ritu gas-filled separator and the great focal-plane spectrometer at the University of Jyvaskyla. A new isomer with t 1 / 2 = 328 ( 2 ) ns was observed and states associated with π d 3 / 2 − 1 , π s 1 / 2 − 1 , π f 7 / 2 + 1 and π h 9 / 2 + 1 structures were revealed. The implications of these results on the systematics of π h 9 / 2 + 1 and π f 7 / 2 + 1 intruder structures in the odd-mass gold isotopes are discussed. The minimum of th…

A new plunger device to measure lifetimes of unbound states in tagged exotic nuclei

A new plunger device has been designed and is being built at the University of Manchester to measure lifetimes of unbound states in exotic nuclei approaching the proton drip-line. The device is designed to work in both vacuum and gas environments and will be used in conjunction with the gas filled separator RITU and the vacuum-mode separator MARA at the University of Jyvaskyla, Finland. This will enable the accurate measurement of excited state lifetimes identified via isomer and charged-particle tagging. The plunger will be used to address many key facets of nuclear structure physics with particular emphasis on the effect of deformation on proton emission rates.

Isomeric and ground-state properties of78171Pt,76167Os, and74163W

Decay paths, half-lives, and excitation energies of the i(13/2) bandheads of the neutron-deficient nuclei Pt-171, Os-167, and W-163 have been established for the first time. Gamma-ray transitions, ...

A study of fusion - fission atZ= 107

An experiment was performed with the EUROGAM II array to investigate the reaction channels that are open in the fusion of a beam on the actinide target at a series of energies around the Coulomb barrier. The symmetric fission products identified from the level structures seem to suggest that a proton and neutrons are emitted prior to fission.

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…

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…

Fine structure in the alpha decays of 226U and 230Pu

The nuclei 226U and 230Pu have been populated via reactions involving 208Pb targets bombarded by 22Ne and 26Mg projectiles. Fusion-evaporation residues were separated in-flight using a gas-filled recoil separator. A position-sensitive Si-strip detector was employed at the focal plane in order to identify correlated α-decay chains. Two fine structure α-decay lines have been observed. The first, with an energy of 7385(5) keV, is assigned as the α decay from 226U to the first excited 2+ state of 222Th. The second line, observed for the first time in this work, has an energy of 6961(30) keV and is assigned as the α decay from 230Pu to the first excited 2+ state of 226U. The excitation energy of…

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…

Decay of aπh11/2⊗νh11/2microsecond isomer in61136Pm75

An experiment has been performed to populate several extremely neutron-deficient nuclei around the mass-140 region of the nuclear chart, using a beam of {sup 54}Fe on a {sup 92}Mo target at an energy of 315 MeV. Analysis of these data using recoil-isomer tagging has established that the yrast {pi}h{sub 11/2} x {nu}h{sub 11/2},J{sup {pi}}=(8{sup +}), bandhead state in {sup 136}Pm is isomeric with a half-life of 1.5(1) {mu}s. This isomeric state decays via a 43-keV, probable-E1 transition to a J{sup {pi}}=(7{sup -}) state. Consideration of the theoretical Nilsson orbitals near the Fermi surface suggests that the J{sup {pi}}=(8{sup +}) state has a {nu}h{sub 11/2}[505](11/2){sup -} x {pi}h{sub …

Can EMMA solve the puzzle of the knee?

Abstract The knee is a change in the slope of the cosmic ray spectrum at approximate energy of 3 PeV. There are multiple competing models for the knee giving conflicting predictions about this change for different masses of the primary particle. Accurate mass measurements of cosmic rays spectra around 3 PeV would be able to exclude some of these models. Cosmic-ray experiment EMMA uses a new method for studying the composition of cosmic rays at the knee area. It is able to determine the multiplicity, the lateral distribution, and the arrival direction of incoming muons produced early in the shower evolution on an event-by-event basis and deduce from these measurements the mass and the energy…

Spectroscopic study of228-234Th nuclei using multi-nucleon transfer reactions

Light-actinide nuclei in the octupole deformed region have been populated using multi-nucleon transfer from Th. The energy level schemes of several thorium isotopes with A = 228-234 have been extended up to and negative parity states have been observed for the first time in Th. A systematic study of the difference in alignment between the positive- and negative-parity bands in thorium nuclei in this mass region shows that Th behave like octupole vibrators, in contrast with Th, which are octupole-deformed in character. An intrinsic electric dipole moment has been measured for the first time in Th. The small value obtained is consistent with the vibrational description of this nucleus.

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.

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…

In-beam electron spectrometer used in conjunction with a gas-filled recoil separator

The conversion-electron spectrometer SACRED has been redesigned for use in conjunction with the RITU gas-filled recoil separator. The system allows in-beam recoil-decay-tagging (RDT) measurements of internal conversion electrons. The performance of the system using standard sources and in-beam is described.

High-Kstructure inFm250and the deformed shell gaps atN=152andZ=100

The structure of high-spin and nonyrast states of the transfermium nucleus $^{250}\mathrm{Fm}$ has been studied in detail. The isomeric nature of a two-quasiparticle excitation has been exploited in order to obtain spectroscopic data of exceptional quality. The data allow the configuration of an isomer first discovered over 30 years ago to be deduced, and provide an unambiguous determination of the location of neutron single-particle states in a very heavy nucleus. A comparison to the known two-quasiparticle structure of $^{254,252}\mathrm{No}$ confirms the existence of the deformed shell gaps at $N=152$ and $Z=100$.

A NEW PLUNGER DEVICE FOR INVESTIGATING THE EFFECTS OF DEFORMATION ON PROTON EMISSION RATES VIA LIFETIME MEASUREMENTS

A new plunger device has been designed and built to measure the lifetimes of unbound states in exotic nuclei beyond the proton drip-line. The device is designed to work in both vacuum and dilute-gas environments made possible through the introduction of a lowvoltage piezoelectric motors. The differential plunger for unbound nuclear states, DPUNS, will be used in conjunction with the gas-filled separator RITU and the vacuum separator MARA at the accelerator laboratory of the University of Jyvaskyla, Finland, to measure the lifetimes of excited states with low population cross-sections. This is achieved by eliminating the need for a carbon foil to isolate the helium gas of RITU from the beam …

Isomer-tagged differential-plunger measurements in proton-unbound 144Ho

The lifetime of an excited state above a weakly populated isomer in the proton-unbound odd-odd nucleus 144Ho has been measured using the recoil distance Doppler shift method. This measurement represents the first differential-plunger lifetime measurement to utilize recoil-isomer tagging. The first excited I[pi]=(10+) state above the two-quasiparticle [pi]h11/2[circle times operator][nu]h11/2(8+) isomer was determined to have a lifetime of [tau]=6(1)�ps. Potential energy surface calculations, based on the configuration-constrained blocking method, predict the isomeric state to have [gamma]-soft triaxial-nuclear shape with [gamma][approximate]24�. The lifetime of the (10+) state can be unders…

News on 12C from beta-decay studies

We discuss the importance of the spectroscopic properties of the resonances of 12C just above the 3α-threshold, and review the existing experimental information of this region with emphasis on O+ and 2+ states. A new experimental approach for studying the β-decays of 12B and 12N is presented based on techniques developed in the context of Radioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given. © 2004 Published by Elsevier B.V.

Shape coexistence in183Tl

Prompt and delayed $\ensuremath{\gamma}$ rays originating from the neutron deficient nucleus ${}^{183}\mathrm{Tl}$ have been observed using the recoil-decay tagging and recoil gating techniques. The band-head energy of the prolate $\ensuremath{\pi}{i}_{13/2}$ yrast band has been determined. The yrast structure has also been confirmed up to the ${(33/2}^{+})$ state. In addition, a candidate for the ${(11/2}^{\ensuremath{-}})$ level based on the $\ensuremath{\pi}{(h}_{11/2}{)}^{\ensuremath{-}1}$ configuration has been observed.

Level structure above the 17+ isomeric state in Tm8369152

Decays of110Rhand112Rhto the near neutron midshell isotopes110Pdand112Pd

The decays ${}^{110}\mathrm{Rh}$ and ${}^{112}\mathrm{Rh}$ have been investigated using on-line mass separation with the ion-guide technique. Extended decay schemes have been constructed for both the low- and high-spin states in ${}^{112}\mathrm{Rh}$. Mixing ratios for the collective transitions from the ${2}_{2}^{+}$ and ${3}_{1}^{+}$ states in ${}^{112}\mathrm{Pd}$ have been measured by $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ angular correlation. The presence of two sets of ${0}^{+}$ and ${2}^{+}$ states in the 1.1\char21{}1.4 MeV range suggests the existence of an intruder band, the energy of which is the lowest in ${}^{110}\mathrm{Pd}$ with two neutrons fewer than the mid…

The isomeric structure of132Pr

The isomeric structure of the neutron deficient nucleus 132Pr, located in the rare-earth region of the nuclear chart, has been studied with the 98Mo(40Ar,5pn)132Pr reaction at beam energies of 150, 158 and 165 MeV. The experiment was performed at the University of Jyvaskyla, Finland where the 40Ar beam was accelerated onto the target by the K130 cyclotron. The JUROGAM II HPGe detector array was employed in conjunction with the RITU gas-filled recoil separator. The focal-plane chamber housed a multi wire proportional counter and a position-sensitive silicon strip detector used for the implantation and identification of recoiling nuclei. The recoil-isomer tagging technique was used to correla…

Characterizing the atomic mass surface beyond the proton drip line viaα-decay measurements of theπs1/2ground state of165Re and theπh11/2isomer in161Ta

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…

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

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 r ...

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

WOS: 000286708700015

Lifetime measurements and shape coexistence inDy144

The known level scheme of {sup 144}Dy has been extended and lifetime measurements have been made with the recoil-distance Doppler-shift method. Reduced transition probabilities and deformations have been determined for four low-lying transitions. These states form part of the first observed band crossing, giving information on the change in nuclear deformation resulting from the rearrangement of h{sub 11/2} protons in the nucleus. Two bands built upon excited 10{sup +} states have been assigned pi(h{sub 11/2}){sup 2} prolate and nu(h{sub 11/2}){sup -2} oblate configurations with tau=12(2)ps and 0.01<tau < or approx. 16ns, respectively. These long lifetimes are reasoned to be a result of sha…

Electromagnetic transitions andαdecay of the223Panucleus

Actinides with $N\ensuremath{\sim}132$ present the best explored region of pear shape nuclei. Still almost no spectroscopic information is available for the heaviest elements, $Z=91--98,$ which are predicted to be octupole instable. The lack of data for the latter nuclei results from the high fission probability encountered in the heavy-ion reactions used to populate them. In order to overcome this handicap, an $\ensuremath{\alpha}$-decay tagging technique was used to identify $\ensuremath{\gamma}$ rays in ${}^{223}\mathrm{Pa}$ produced through the ${}^{208}\mathrm{Pb}{(}^{19}\mathrm{F},4n)$ reaction. A new value of 4.9(4) ms for the half-life of ${}^{223}\mathrm{Pa}$ was obtained as a by-p…

Strongly coupled bands in the neutron-deficient nucleus167Re

Excited states in the neutron-deficient nucleus Re-167 have been observed in a recoil-tagging experiment performed with the Jurosphere gamma-ray spectrometer in conjunction with the RITU gas-filled ...

Transition probability studies in175Au

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.

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…

Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line

A multiparticle spin-trap isomer has been discovered in the proton-unbound nucleus Ta85 73158. The isomer mainly decays by γ-ray emission with a half-life of 6.1(1) μs. Analysis of the γ-ray data shows that the isomer lies 2668 keV above the known 9+ state and has a spin 10 higher and negative parity. This 19- isomer also has an 8644(11) keV, 1.4(2)% α-decay branch that populates the 9+ state in Lu154. No proton-decay branch from the isomer was identified, despite the isomer being unbound to proton emission by 3261(14) keV. This remarkable stability against proton emission is compared with theoretical predictions, and the implications for the extent of observable nuclides are considered. © …

Competing quasiparticle configurations in W-163

WOS: 000274002700019

Five-valence-protonN=82isotone137Cs

Yrast excitations in the N=82 isotone {sup 137}Cs have been identified for the first time in thick-target {gamma}-ray coincidence measurements for the system {sup 232}Th+{sup 136}Xe using the Gammasphere array. The {sup 137}Cs nuclei were produced in deep inelastic one-proton-transfer reactions. By-products of the main investigation were two well-developed rotational bands which were identified in heavy reaction partner products complementary to {sup 137}Cs and are tentatively assigned to the little studied nucleus {sup 231}Ac. There was no difficulty in placing the 11 observed {sup 137}Cs transitions in a yrast level scheme extending to an I{sup {pi}}=(31/2{sup {minus}}) level at 5494 keV.…

Fine structure in Po α-decay and shape coexistence in Pb

Abstract Excited Jπ=0+ states in 188 Pb populated in the α-decay of 192 Po have been identified through α-particle/conversion electron coincidences. α-particle energies and branching ratios have been measured, and hindrance factors deduced. The level scheme has been fitted using a configuration mixing calculation, providing estimates of the mixing matrix elements, mixing amplitudes and the energies of unperturbed and unobserved levels.

Probing intruder structures in lead nuclei

In-beam γ-ray spectroscopy measurements provide important information on coexisting normal and intruder configurations in lead nuclei. However, in these experiments the yrast states are preferentially populated so that in many cases nothing is known about non-yrast states that are essential for obtaining a fuller understanding. Complementary experiments designed to study fine structure in the a decays of polonium nuclei have led to the discovery of low-spin non-yrast states in the daughter lead nuclei, while higher-spin states can be identified through the γ decays of isomeric states. The α-decay studies have the additional benefit of allowing information on configuration mixing in the polo…

Recoil-isomer tagging techniques at RITU

Techniques have been developed to study isomeric states in nuclei with the use of RITU (gas filled separator) at the University of Jyvaskyla. The first was the recoil-isomer tagging technique initially, utilised by D.M. Cullen to study the K π = 8− isomeric state in 138Gd [1]. The juro-sphere array was employed in conjunction with ritu and a focal plane array which consisted of several Compton-suppressed Germanium detectors, placed in close geometry around a multi wire proportional counter (mwpc) and a silicon strip detector used for the implantation of recoiling nuclei. This technique correlates prompt and delayed γ-ray transitions across isomeric states and identifies the lifetime of the …

First observation of excited states in182Pb

First prompt in-beam γ-ray spectroscopy of a superheavy element: the256Rf

Using state-of-the-art γ-ray spectroscopic techniques, the first rotational band of a superheavy element, extending up to a spin of 20 , 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 s…

Level structure of 99Nb

The β decay of 97Sr to 97Y has been investigated using ion-guide on-line mass separation and a 10 Ge-detector array to record γ−γ coincidences to a detection limit well below that of former studies. Similarities are found in the β-decay patterns of 99Zr and of its isotone 97Sr and also in the γ-ray decay rates and branchings of the corresponding levels in their respective daughters 99Nb and 97Y. This indicates a persisting influence of the d5/2 neutron shell closure for 99Nb. The level structure of 99Nb and the β-feeding pattern are discussed in the frame of the interacting boson-fermion plus broken pair model and the microscopic quasiparticle phonon model.

Lifetime measurements probing triple shape coexistence in ^{175}Au

Lifetimes of the low-lying excited states in the very neutron-deficient nucleus ${}^{175}$Au have been measured by the recoil-distance Doppler-shift method using $\ensuremath{\gamma}$-ray spectra obtained with the recoil-decay tagging technique. Transition quadrupole moments and reduced transition probabilities extracted for this odd-$Z$ nucleus indicate the existence of three different shapes and the competition between collective and noncollective structures.

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…

Low-lying excited states in the neutron-deficient isotopes163Os and165Os

Excited states in the neutron-deficient isotopes Os-163 and Os-165 were identified using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. The Os-163 and Os-165 nuclei were populated via the Cd-106(Ni-60,3n) and Mo-92(Kr-78,2p3n) 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 f(7/2) and h(9/2) orbitals.

α-Decay branching ratios measured by γ-ray tagging

Abstract The nuclides 168–170Pt were produced by bombarding isotopically enriched 92,94Mo targets with 336, 348 MeV 78Kr ions. Prompt γ rays were detected at the target position and provided a selection criterion for the 168–170Pt nuclei. This technique enables the problem of the background from higher-energy α decays in the spectrum to be circumvented. The Pt nuclei were separated in flight using the gas-filled separator RITU and implanted into the GREAT spectrometer, which was used to study subsequent α decays. The α -decay branching ratios of 164–166Os were deduced from the fraction of selected 168–170Pt nuclei correlated with α decays of 164–166Os. The resulting branching ratios agree w…

First observation of excited states inPo192

\ensuremath{\gamma} rays following the $^{160}\mathrm{Dy}$${(}^{36}$Ar,4n${)}^{192}$Po reaction have been identified by employing a high-transmission gas-filled separator in recoil decay tagging measurements. The deduced level scheme reveals a flattening of the energy systematics, when going towards the neutron midshell indicating that the deformed intruder structures have become yrast. \textcopyright{} 1996 The American Physical Society.

Rotational features of vibrator nucleus118Te

High-spin states in ${}^{118}\mathrm{Te}$ have been populated via heavy-ion induced reactions. Excited states were observed up to $I=32\ensuremath{\Elzxh}$ and, in addition to irregular level sequences, several bands were identified for the first time. The decoupled negative parity bands based upon ${7}^{\ensuremath{-}}$ and ${8}^{\ensuremath{-}}$ states are interpreted to arise from the proton ${h}_{11/2}{g}_{7/2}$ configuration coupled to the $2p\ensuremath{-}2h$ intruder states in ${}^{116}\mathrm{Sn}.$ These bands show very smooth alignment behavior, in accordance with the proton ${h}_{11/2}$ bands in neighboring Sb and I nuclei. Above $I=20$ the yrast positive parity band is built on t…

Identification of low-lying proton-based intruder states in189–193Pb

Low-lying proton-based intruder states have been observed in the odd-mass isotopes Pb-189,Pb-191,Pb-193 in experiments at the RITU gas-filled recoil separator. The identification has been performed ...

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 ...

Conversion electron spectroscopy of magnetic-rotational bands in 197Pb and 199Pb

Magnetic–rotational bands in the nearly spherical nuclei 197Pb and 199Pb and their decay to the normal states have been investigated by in–beam conversion electron spectroscopy following (heavy ion,xn) reactions. The expected M1 multipolarity of the in–band transitions has been confirmed for the strongest bands and the multipolarity of several transitions in the decay of the bands has been determined.

Excited states in the proton-unbound nuclide Ta-158

Excited states in the neutron-deficient odd-odd proton-unbound nuclide $^{158}\mathrm{Ta}$ have been investigated in two separate experiments. In the first experiment, $^{166}\mathrm{Ir}$ nuclei were produced in the reactions of 380 MeV $^{78}\mathrm{Kr}$ ions with an isotopically enriched $^{92}\mathrm{Mo}$ target. The $\ensuremath{\alpha}$-decay chain of the ${9}^{+}$ state in $^{166}\mathrm{Ir}$ was analyzed. Fine structure in the $\ensuremath{\alpha}$ decay of the ${9}^{+}$ state in $^{162}\mathrm{Re}$ established a 66 keV difference in excitation energy between the lowest-lying ${9}^{+}$ and ${10}^{+}$ states in $^{158}\mathrm{Ta}$. Higher-lying states in $^{158}\mathrm{Ta}$ were popul…

Mass-140 isomers near the proton dripline

An experiment has been performed in Jyvaskyla, Finland, using Jurogam in conjunction with RITU and GREAT. This experiment populated several extremely neutron-deficient nuclei around the mass-140 region of the nuclei chart, using the 92Mo(54Fe, α2n) reaction at 245 MeV. Analysis of these data has revealed several previously unobserved isomeric states, in several nuclei. One of these has been assigned to 143Dy with a half-life of 1.2 ± 0.3 µs. The energies of the prompt γ rays in the band built upon the isomer are in agreement with those previously observed.

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…

Decay studies ofAu170,171,Hg171–173, andTl176

The $^{170,171}\mathrm{Au}$ isotopes were produced in the fusion-evaporation reaction of a $^{78}\mathrm{Kr}$ ion beam with a $^{96}\mathrm{Ru}$ target. For $^{170}\mathrm{Au}$ the proton and $\ensuremath{\alpha}$ emission from the ground state were observed for the first time and the decay of the isomeric state was measured with improved accuracy. In addition, the decay of $^{171}\mathrm{Au}$ was measured with high statistics. A new $\ensuremath{\alpha}$-emitting nucleus $^{171}\mathrm{Hg}$ and the previously known $^{172}\mathrm{Hg}$ and $^{167,168,169,170}\mathrm{Pt}$ isotopes were also studied. The ground-state proton emission was identified for a new proton emitter $^{176}\mathrm{Tl}$ …

Development of the Jyväskylä microbeam facility

Abstract A new microbeam facility is being constructed at the 1.7 MV Pelletron Accelerator in Jyvaskyla. The facility is designed for easy upgrading and incorporates a number of innovative features. Initially, it is based on a Heidelberg doublet with a design capability of a 3 × 5 μm beamspot at PIXE intensities and later upgraded to nanobeam performance. A thermal-expansion compensated rigid frame mounted on a mechanically isolated floor section is used to support the ion optical components. A compact-post focusing electrostatic deflector is used for high linearity beam scanning. This together with a novel time-stamped data collection (TDC) allows dynamic effects in IBIC, fluorescence blea…

New interpretation of shape coexistence in99Zr

Levels in ${}^{99}\mathrm{Zr}$ populated by $\ensuremath{\beta}$ decay of on-line mass separated ${}^{99}$Y have been studied by $\ensuremath{\gamma}$-ray spectroscopic methods, including $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences recorded with an array of ten Ge detectors and level-lifetime measurements. The formerly reported strongly collective character of the 53-keV transition turns out to be questionable. This implies a revision of the experimental evidence for shape coexistence in ${}^{99}\mathrm{Zr}.$ Transition rates and $\ensuremath{\gamma}$-ray branching ratios make a new level at 679 keV with ${t}_{1/2}=9$ ns another candidate for a deformed state.

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 ${T}_{1/2}$ $=$…

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…

Identification of theKπ=8−rotational band in138Gd

A ${K}^{\ensuremath{\pi}}{=8}^{\ensuremath{-}}$ collective rotational band has been established upon the 6 $\ensuremath{\mu}$s isomeric state in the very neutron-deficient nucleus ${}^{138}\mathrm{Gd}.$ The band was observed using a technique involving the correlation of $\ensuremath{\gamma}$-ray transitions across the isomeric state. The single-particle configuration of the isomer has been deduced from the $\ensuremath{\Delta}I=2$ to $\ensuremath{\Delta}I=1$ intensity branching ratios. In addition, a series of other $\ensuremath{\gamma}$-ray transitions were observed which are reasoned to be part of a higher-lying four quasiparticle structure which decays through the ${K}^{\ensuremath{\pi}…

Underground multi-muon experiment EMMA

EMMA is a new experiment designed for cosmic- ray composition studies around the knee energy operating at the shallow depth underground in the Pyh¨ asalmi mine, Fin- land. The array has sufficient coverage and resolution to de- termine the multiplicity, the lateral density distribution and the arrival direction of high-energy muons on an event by event basis. Preliminary results on the muon multiplicity ex- tracted using one detector station of the array are presented.

Clarification of the Three-Body Decay ofC12(12.71 MeV)

Using $\ensuremath{\beta}$ decays of a clean source of $^{12}\mathrm{N}$ produced at the IGISOL facility, we have measured the breakup of the $^{12}\mathrm{C}$ (12.71 MeV) state into three $\ensuremath{\alpha}$ particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.

Coexisting structures in 115Sn and 116Sn

Abstract Excited states up to I ≈ 20 in 115 Sn and 116 Sn, populated via the ( 18 O, αxn) reactions, have been studied using the DORIS Ge detector array in conjunction with charged particle detectors. In both nuclei, spherical as well as regular, deformed level structures were found. The spherical states are interpreted to arise from pure neutron configurations, while the deformed, intruder bands obviously involve proton 2p-2h excitations across the Z = 50 shell gap.

Identification of Excited States in theTz=1NucleusXe110: Evidence for Enhanced Collectivity near theN=Z=50Double Shell Closure

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient (N=Z+2) nucleus {sup 110}Xe, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited 2{sup +} and 4{sup +} level energies as a function of the decreasing neutron number as the N=50 major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar n-p interactions becoming increasingly important close to the N=Z line.

Experimental investigation of the 02+ band in Sm154 as a β-vibrational band

Abstract A study of Sm 154 through γ -ray and internal conversion electron coincidence measurements was performed using the Silicon And GErmanium spectrometer (SAGE). An upper limit for the ρ 2 ( E 0 ; 2 2 + → 2 1 + ) and measurement of the ρ 2 ( E 0 ; 4 2 + → 4 1 + ) monopole transitions strengths were determined. The extracted transition strength for each is significantly lower than that predicted by either the Bohr and Mottelson β -vibration description or the interacting boson model. Hence, the long standing interpretation of these states as a collective band built on the 0 2 + state, which is conventionally assigned as a Bohr and Mottelson β vibration is questionable.

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…

Probing structural changes in the very neutron-deficient Os isotopes with recoil-decay tagging

In recent years, the exploitation of the iecoil-decay tagging (RDT) technique with,large arrays of germanium detectors has revealed much information about the structure of heavy nuclei approaching the proton drip line. The yrast bands of the N <= 93 osmium isotopes have been identified in a campaign of tagging experiments using various spectrometer arrays coupled to the RITU gas-filled separator based at the University of Jyvaskyla. Trends in the yrast state excitation energies have indicated a transition from gamma-soft triaxial to near-spherical shapes with decreasing neutron number. Recent experimental results for Os-162 obtained with the JUROGAM and GREAT spectrometers also indicate the…

Investigation into the Effects of Deformation on Proton Emission Rates via Lifetime Measurements

Spectroscopy of very neutron-deficient 187,189Bi isotopes

Shape coexistence is well known to occur in nuclei, in particular near closed shells [1], where particle-hole excitations across the shell gap can create deformed intruder states. In the neutron-deficient lead isotopes (Z = 82), deformed structures appear at low excitation energy. The isotope 188Pb [2] shows for example a triple shape coexistence with oblate and prolate excited 0+ states that compete with the spherical ground state. The study of the odd-proton single-particle excitations in Bi isotopes allows to obtain information on the orbitals involved in the different shapes observed in this mass region.

Recoil decay tagging ofγrays in the extremely neutron-deficient nucleusOs162

The neutron-deficient nucleus $^{162}\mathrm{Os}$, produced in the $^{106}\mathrm{Cd}(^{58}\mathrm{Ni},2n)$ reaction, has been studied using the JUROGAM $\ensuremath{\gamma}$-ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal plane spectrometer. $\ensuremath{\gamma}$-ray transitions in $^{162}\mathrm{Os}$ have been assigned for the first time through the application of the recoil decay tagging technique. The excitation energy of the ${2}^{+}$ state and the tentative energy of the ${8}^{+}$ state are discussed in terms of the systematic energy trends as the $N=82$ shell gap is approached.

Lifetimes of odd-spin yrast states inHg182

Lifetimes of excited states in $^{182}\mathrm{Hg}$ were extracted from recoil-gated $\ensuremath{\gamma}$-ray spectra and recoil-gated $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence matrices using the recoil distance Doppler-shift method. States were populated using the $^{96}\mathrm{Mo}$($^{88}\mathrm{Sr}$,$2n$)$^{182}\mathrm{Hg}$ fusion-evaporation reaction. Measured lifetimes allowed transition probabilities, transition quadrupole moments, quadrupole deformation parameters, and transition dipole moments to be deduced for the band formed by the odd-spin yrast states. The experimental results confirm the low degree of octupole collectivity in this mass region.

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…

Nuclear levels in proton-unboundI109: Relative single-particle energies beyond the proton drip line

A level scheme has been constructed for the proton-unbound, T-z=3/2 nuclide I-109(53)56 following a recoil-decay-tagging experiment using the Ni-58(Fe-54, p2n gamma) reaction at a beam energy of 19 ...

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…

Comparison of gamma-ray coincidence and low-background gamma-ray singles spectrometry

Aerosol samples have been studied under different background conditions using gamma-ray coincidence and low-background gamma-ray singles spectrometric techniques with High-Purity Germanium detectors. Conventional low-background gamma-ray singles counting is a competitive technique when compared to the gamma-gamma coincidence approach in elevated background conditions. However, measurement of gamma-gamma coincidences can clearly make the identification of different nuclides more reliable and efficient than using singles spectrometry alone. The optimum solution would be a low-background counting station capable of both singles and gamma-gamma coincidence spectrometry.

Isomer spectroscopy in254No

Isomeric states in No-254 were investigated using a calorimetric method. Two different isomers were found with half-lives of T-1/2 = 266 +/- 2 ms and T-1/2 = 184 +/- 3 mu s, respectively. The domin ...

Low-lying shears bands in very light odd—odd Bi isotopes

The concept of magnetic rotation in nuclei was introduced to explain the observed regular bands with enhanced M1 transitions and weak or absent E2 crossover transitions in nearly spherical nuclei around 198Pb [1]. These bands can be described by the coupling of high-j proton and neutron configurations to a total spin tilted at an angle of ~ 45° with respect to the symmetry axis. As the proton and neutron spins align with increasing excitation energy, a sequence of ΔI = 1 levels of fixed parity (“shears band”) is formed [2].

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 ...

Isomeric states in proton-unbound 187, 189Bi isotopes

Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes 187, 189Bi has been performed using the Recoil Decay Tagging (RTD) method. The isomeric i 13/2 states have been identified and their lifetimes have been measured. The systematics of these long-lived M2 isomers has been extended to the proton-unbound isotopes. The general behaviour of single-proton states is discussed within the systematics and interpreted within the shell-model framework.

Recent applications of the JYFL gas-filled recoil separator

Abstract The gas-filled recoil separator RITU at the Department of Physics, University of Jyvaskyla (JYFL) was constructed in 1992–1993, and the first experiments were performed in late 1993. RITU differs from other gas-filled separators by having a vertically focusing quadrupole magnet in front of the separating dipole for better matching with the dipole acceptance. New results from RITU include the discovery of 13 previously unpublished isotopes of At, Rn, Fr, Ra, Ac and Th, while experiments in the transuranium region have also been made. Illustrative examples from these studies together with results on background properties, efficiency of separation, and other performance data will be p…

Discovery of 157W and 161Os

The nuclides W-157 and Os-161 have been discovered ill reactions of Ni-58 ion beams with a Cd-106 target. The Os-161 alpha-decay energy and half-life were 6890 +/- 12 keV and 640 +/- 60 mu s. The d ...

Combined in-beam electron andγ-ray spectroscopy ofHg184,186

By exploiting the SAGE spectrometer a simultaneous measurement of conversion electrons and {gamma} rays emitted in the de-excitation of excited levels in the neutron-deficient nuclei {sup 184,186}Hg was performed. The light Hg isotopes under investigation were produced using the 4n channels of the fusion-evaporation reactions of {sup 40}Ar and {sup 148,150}Sm. The measured K- and L-conversion electron ratios confirmed the stretched E2 nature of several transitions of the yrast bands in {sup 184,186}Hg. Additional information on the E0 component of the 2{sub 2}{sup +}{yields}2{sub 1}{sup +} transition in {sup 186}Hg was obtained.

Access to Gamma-ray Spectroscopy of Neutron-Rich sdfp Shell Nuclei

γ-rays in neutron-rich sdfp shell nuclei, produced in deep-inelastic processes during collisions of 37Cl and 40Ar ions on 208Pb and of 48Ca ions on 48Ca, have been studied using large Ge multidetector arrays. Candidates for new yrast states in heavy argon and sulfur isotopes have been identified.

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…

Probing the limit of nuclear existence: Proton emission from 159Re

WOS: 000240847400007

A facility for fast-neutron irradiations at Jyväskylä and its use for nuclide cross-section measurements in fission

Abstract An efficient and reliable transport system for fast-neutron irradiations has been built at the Physics Department, Jyvaskyla, Finland. It is constructed from commercial bicycle components and is driven by a computer-controlled stepping motor. It can be operated in single or cyclic mode. The neutron irradiated targets are moved within 1.2 s (full stop to full stop) to a well-shielded position 3 m away where they can be removed or directly investigated by γ spectroscopy. The system has been built with the aim to experimentally verify the calculated production rates of neutron-rich nuclei in the SPIRAL2 uranium target. However, the facility can be used for various kinds of fast-neutro…

Confirming band assignments in $^{167}$ytterbium with gamma-gamma-electron triple-coincidence spectroscopy

International audience; Multipolarity measurements are presented for transitions in the deformed odd-mass nucleus$^{167}$ Yb in support of tentative spin assignments and level interpretations based upon the cranked-Nilsson model. Internal-conversion coefficients were measured with the SAGE (Silicon And GErmanium) spectrometer confirming several E2 transition assignments. The array of high-purity germanium detectors enabled the recording of high-multiplicity events from which $\gamma\gamma\gamma$ and $\gamma\gamma e^{-}$ data sets were extracted and the technique of high-fold $\gamma$ -ray gating was demonstrated to cleanly isolate transitions of interest.

Gamma-spectroscopy of the 199At nucleus with the recoil filter detector

The neutron deficient 199At nucleus has been studied in the 175Lu+28Si reaction at Eb= 141 MeV. In order to select events of interest in the presence of the very strong background caused by fission, γ-rays have been detected in coincidence with recoiling evaporation residues. The excited states of 199At observed for the first time may indicate that this nucleus is deformed.

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…

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.

Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of theZ=104NucleusRf256

The rotational band structure of the $Z=104$ nucleus $^{256}\mathrm{Rf}$ has been observed up to a tentative spin of $20\ensuremath{\hbar}$ using state-of-the-art $\ensuremath{\gamma}$-ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-$j$ orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing i…

Lifetimes of intruder states in 186Pb, 188Pb and 194Po

Abstract Lifetimes of prolate intruder states in 186Pb and 188Pb and oblate intruder states in 194Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of | β 2 | = 0.29 ( 5 ) and | β 2 | = 0.17(3) have been extracted from experimental B ( E 2 ) values for the prolate and the oblate bands, respectively. The present study addresses the phenomenon of shape coexistence typical for the nuclei near Z = 82 and N = 104 , providing information on configuration mixing of intrinsic structures of the nuclei of interest. The results are compared with the available lifetime data and theoretical results for neutron-deficient Po, Pb, Hg and Pt nuclei. …

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.

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.

γ-ray spectroscopy approaching the limits of existence of atomic nuclei: A study of the excited states ofPt168andPt169

Excited states in the $N=90$ and $N=91$ Pt nuclei have been investigated using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. These nuclei were populated via the reactions $^{92}\mathrm{Mo}(^{78}\mathrm{Kr},2n)$ and $^{94}\mathrm{Mo}(^{78}\mathrm{Kr},3n)$ at 335 and 348 MeV, respectively. The recoil-decay tagging technique has been used to correlate prompt $\ensuremath{\gamma}$ radiation with the characteristic $\ensuremath{\alpha}$ decays of $^{168}\mathrm{Pt}$ and $^{169}\mathrm{Pt}$. A $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ analysis has allowed a level scheme for $^{168}\mathrm{Pt}$ to be reported for the first time and the l…

α decay studies of the nuclidesU218andU219

Very neutron deficient uranium isotopes were produced in fusion evaporation reactions using $^{40}\mathrm{Ar}$ ions on $^{182}\mathrm{W}$ targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam and other reaction products. 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 $\ensuremath{\alpha}$-decaying states, with ${E}_{\ensuremath{\alpha}}=(8612\ifmmode\pm\else\textpm\fi{}9)$ keV and ${T}_{1/2}=(0.{51}_{\ensuremath{-}0.10}^{+0.17})$ ms for t…

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.

Recent developments at the RITU focal plane

Several technical developments have recently taken place at the RITU [1] focal plane detector system. Due to these developments the gas-filled recoil separator RITU is now, in the best case, up to an order of magnitude more sensitive than before.

Yrast structures in the light Pt isotopes169–173Pt

The exploitation of the recoil-decay tagging (RDT) technique has reinvigorated experimental investigations of the shape coexistence phenomenon in heavy neutron-deficient nuclei. In a recent experiment using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator, excited states have been investigated in the light platinum isotopes. In addition to extending the yrast sequences in 170Pt and 172Pt, the first observation of excited states in the odd-N isotopes, 169Pt and 173Pt, is reported. The bands are discussed in terms of trends in level excitation energies as a function of neutron number.

αdecay studies of very neutron-deficient francium and radium isotopes

Very neutron-deficient francium and radium isotopes have been produced in fusion evaporation reactions using $^{63}\mathrm{Cu}$ and $^{65}\mathrm{Cu}$ ions on $^{141}\mathrm{Pr}$ targets and $^{36}\mathrm{Ar}$ ions on $^{170}\mathrm{Yb}$ 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 decays. Two new \ensuremath{\alpha} decaying radium isotopes, $^{201}\mathrm{Ra}$ and $^{202}\mathrm{Ra}$, were identi…

High-Kfour-quasiparticle states inGd138

States above the known ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$ 6 $\ensuremath{\mu}$s isomer in $^{138}\mathrm{Gd}$ have been populated with the $^{106}\mathrm{Cd}$($^{36}\mathrm{Ar}$,$2p2n$) reaction at a beam energy of 180 MeV at the University of Jyv\"askyl\"a, Finland. The recoil-isomer tagging technique was utilized to correlate delayed $\ensuremath{\gamma}$-ray decays, detected in the GREAT focal plane spectrometer, with prompt decays measured in the JUROGAM II spectrometer at the target position. The lifetime of the ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$ isomeric state has been remeasured as 6.2(2) $\ensuremath{\mu}$s. Two high-lying strongly coupled bands have been estab…

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.

First observation of excited states in the neutron deficient nuclei Pt and Pt

Abstract Excited states have been observed for the first time in 168 Pt and 170 Pt using the α -decay recoil-tagging technique. The trend of decreasing deformation moving away from the N =104 mid-shell continues for 170 Pt but the structure of 168 Pt is significantly different. The low spin level energy systematics in 168 – 184 Pt are presented and discussed within the framework of the interacting boson model.

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

WOS: 000290082600015

Identification of the 13/2+ isomer in 199At

The 13/2+ isomeric state in the 199At nucleus has been identified at an excitation energy of 573 keV and its half-life measured to be 580(130) ns using the recoil-decay tagging technique.

Identification of excited states in 167Os and 168Os: shape coexistence at extreme neutron deficiency

Excited states in the very neutron-deficient isotopes Os-167 and Os-168 have been observed using the reaction Sn-112(Ni-58, 2pxn). The JUROSPHERE gamma -ray spectrometer array was used in conjuncti ...

Spectroscopy ofHo144using recoil-isomer tagging

Excited states in the proton-unbound odd-odd nucleus $^{144}\mathrm{Ho}$ have been populated using the $^{92}\mathrm{Mo}(^{54}\mathrm{Fe},\mathit{pn})^{144}\mathrm{Ho}$ reaction and studied using the recoil-isomer-tagging technique. The alignment properties and signature splitting of the rotational band above the ${I}^{\ensuremath{\pi}}=({8}^{+})^{144m}\mathrm{Ho}$ isomer have been analyzed and the isomer confirmed to have a $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ two-quasiparticle configuration. The configuration-constrained blocking method has been used to calculate the shapes of the ground and isomeric states, which are both predicted to have triaxia…

Application of ultra-fast timing techniques to the study of exotic and weakly produced nuclei

Ultra-fast time-delayed techniques have been recently applied in a number of studies where exotic nuclei were identified using advanced selection techniques. These include large Compton-suppressed Ge arrays, in-flight separators or recoil separators. Some of the new results are discussed in this presentation. Besides the results for $^{32}$Mg and $^{96}$Pd, they include the first determination of the half-life of the $8^+$ state in $^{80}$Ge, $T_1/2$ = 2.95(6) ns, and significantly more precise results for $^{51}$Mn (3680 keV level) and $^{48}$V (421 keV level), $T_1/2$ = 1760(40) ps and $T_1/2$ $\leq$ 135 ps, respectively. Development of new scintillators will steadily improve precision an…

The new vacuum-mode recoil separator MARA at JYFL

Abstract A new vacuum-mode recoil separator MARA (Mass Analysing Recoil Apparatus) is under design and construction at the Department of Physics in the University of Jyvaskyla. The separator is intended to separate reaction products from the primary beam in mass region below A = 150 . The ion-optical configuration of the separator will be QQQDEDM, where a magnetic quadrupole (Q) triplet is followed by an electrostatic deflector (DE) and a magnetic dipole (DM). The total length of MARA will be less than 7.0 m and the first order resolving power more than 250 for a beam spot size of 2 mm. In this contribution the main properties of MARA are given and results from simulations are shown.

Lifetime measurement of the first excited2+state in108Te

The lifetime of the first excited 2(+) state in the neutron deficient nuclide (108)Te has been measured for the first time, using a combined recoil decay tagging and recoil distance Doppler shift t ...

Studies of plasma breakdown and electron heating on a 14 GHz ECR ion source through measurement of plasma bremsstrahlung

Temporal evolution of plasma bremsstrahlung emitted by a 14?GHz electron cyclotron resonance ion source (ECRIS) operated in pulsed mode is presented in the energy range 1.5?400?keV with 100??s resolution. Such a high temporal resolution together with this energy range has never been measured before with an ECRIS. Data are presented as a function of microwave power, neutral gas pressure, magnetic field configuration and seed electron density. The saturation time of the bremsstrahlung count rate is almost independent of the photon energy up to 100?keV and exhibits similar characteristics with the neutral gas balance. The average photon energy during the plasma breakdown is significantly highe…

Probing shapes of very neutron deficientZ≈82 nuclei using the recoil-decay tagging method

The JYFL gas-filled recoil separator, RITU, combined with efficient Ge-detector arrays has been employed in in-beam γ-ray studies of very neutron-deficient nuclei close to theZ=82 shell. Gamma-rays from nuclei produced at the few μb cross-section level have been detected.