Identification of yrast states in 187Pb

g -ray spectroscopy of the high-spin states of the neutron-deficient nucleus 187Pb has been conducted with the 155Gd(36Ar,4n) reaction. A cascade of three transitions was deduced from g -g coincidence data gated by detection of recoiling evaporation residues in a gas-filled recoil separator. In an earlier, separate experiment, two of these g rays were positively identified with 187Pb by recoil-g coincidence measurements with a high-resolution, recoil mass spectrometer. From comparison with similar sequences in heavier odd-A lead isotopes, the cascade in 187Pb is associated with the sequence of three E2 transitions from the yrast 25/2 + level to a low-lying 13/2 + isomer. The variation of excitation energy with mass number of the levels concerned suggests that their structure can be associated with weak coupling of an odd i13/2 neutron to states in the spherical well. However, the possibility that they are influenced by mixing with states in the prolate-deformed well cannot be discounted

Decay spectroscopy at the two-proton drip line: radioactivity of the new nuclides 160Os and 156W

The radioactivity of 76160Os84 and 74156W82 that lie at the two-proton drip line have been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58Ni ions bombarding a 106Cd target. The 160Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160Os (Eα = 7092(15) keV, t1/2 = 97−32+97 μs) and its isomeric state (Eα = 8890(10) keV, t1/2 = 41−9+15 μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of 156W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, 156Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in 73156Ta83 of 333−22+25 ms was obtained in a separate experiment using the same experimental systems with a 102Pd target. This result was employed to improve the precision of the half-life determined for 156W, which was measured as 157−34+57 ms

Microsecond isomers in Tl-187 and Pb-188

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between Gd-155 and Ar-36 and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the Tb-159(S-32,4n) reaction the gamma-decay of isomeric levels in Tl-187 has been studied using delayed gamma-gamma coincidence measurements. From observation of their subsequent gamma decay, the mean lifetimes were measured to be 1000+/-55 ns and 1600+/-100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in Pb-188 was also observed and its lifetime was measured as 1150+/-30 ns, and limits of 20-600 ns were placed on the meanlife of an isomer conjectured in Pb-187

Isomer Studies for Nuclei near the Proton Drip Line in the Mass 130-160 Region

This report details the status of an experimental research programme which has studied isomeric states in the mass 130-160 region of the nuclear chart. Several new isomers have been established and characterised near the proton drip Une using a recoil isomer tagging technique at the University of Jyväskylä, Finland. The latest experiments have been performed with a modified setup where the standard GREAT focal-plane double-sided silicon-strip detector was changed to a dual multi-wire proportional-counter arrangement. This new setup has improved capability for short-lived isomer studies where high focal-plane rates can be tolerated. The results of key recent experiments for nuclei situated above (153Yb,152Tm) and below (136Pm,142Tb) the N=82 shell gap were presented along with an interpretation for the isomers. Finally, the future prospects of the technique, using an isomer-tagged differential-plunger setup, were discussed. This technique will be capable of establishing the deformation of the states above the isomers and will aid in the process of assigning underlying single-particle configurations to the isomeric states

Alphaparticle capture reactions in inverse kinematics relevant to p process nucleosynthesis

Expérience GANIL/Spectromètre LISE3International audienc

Identification of yrast states in Pb-187

gamma-ray spectroscopy of the high-spin states of the neutron-deficient nucleus Pb-187 has been conducted with the Gd-155(Ar-36,4n) reaction. A cascade of three transitions was deduced from gamma-gamma coincidence data gated by detection of recoiling evaporation residues in a gas-filled recoil separator. In an earlier, separate experiment, two of these gamma rays were positively identified with Pb-187 by recoil-gamma coincidence measurements with a high-resolution, recoil mass spectrometer. From comparison with similar sequences in heavier odd-A lead isotopes, the cascade in Pb-187 is associated with the sequence of three E2 transitions from the yrast 25/2(+) level to a low-lying 13/2(+) isomer. The variation of excitation energy with mass number of the levels concerned suggests that their structure can be associated with weak coupling of an odd i(13/2) neutron to states in the spherical well. However, the possibility that they are influenced by mixing with states in the prolate-deformed well cannot be discounted. [S0556-2813(98)00411-7]

Recoil Isomer Tagging on Proton-Rich Odd–Odd N=77 Isotones 142Tb and 144Ho

The isomeric structure of the N=77 isotones 14265Tb and 14467Ho have been studied with the 92Mo(54Fe, xpn) fusion evaporation reaction at the University of Jyväskylä. The Jurospehere II germanium array was employed in conjunction with the RITU gas filled recoil separator. The feeding and decay of a 500(20) ns isomeric state in 144Ho has been established for the first time together with states built upon the known 15 μs isomer in 142Tb. The behavior of these new structures above the isomers suggest that they are low deformation configurations which display signs of triaxiality.peerReviewe