New Spins for ground states and isomers in 115^{115}Pd and 117^{117}Pd

Levels in 115Pd and 117Pd nuclei, populated in the spontaneous fission of 248Cm were studied by means of prompt gamma spectroscopy using the EUROGAM2 array of Anti-Compton spectrometers. Negative-parity, I = 9/2 excitations were identified, which are associated with the long-lived isomers in these nuclei, reported previously as 11/2- excitations. The new data indicate spin and parity 3/2 + for ground states in 115Pd and 117Pd instead of 5/2 + proposed in previous works. This result implicates changes of spin assignments to other levels in both nuclei

New information on medium-spin structure of 133Sb

Excited states in the nucleus 133Sb, populated in the fission of 235U induced by thermal neutrons were studied using the Lohengrin fission-fragment separator. A new 4191.8 keV level in 133Sb, populated in the decay of the 16.6 μs isomer, was observed. The level is interpreted as the 11/2+ member of the πg7/2 * core configuration, predicted by the shell model at 4095 keV. Levels corresponding to octupole excitation of the 132Sn core, identified previously in prompt-γ measurement, were now observed in the isomeric decay

Half-life of the 830.2 keV isomer in 97^{97}Sr

The half-life of the 830.2 keV isomeric state in $^{97}$Sr, for which very different values are reported in the literature, has been measured. The experiment performed at the LOHENGRIN fission-frgment separator consisted of two independent measurements. The two measurements provided consistent results. The weighted average value $T_{1/2}$ = 526(13) ns, supports the interpretation of the 830.2 keV state in $^{97}$Sr, as the 9/2+[404] neutron-hole configuration

Nuclear structure studies of microsecond isomers near A = 100

International audienceA large variety of shapes may be observed in Sr and Zr nuclei of the A = 100 region when the number of neutrons increases from N = 58 to N = 64. The lighter isotopes are rather spherical. It is also well established that three shapes co-exist in the transitional odd-A, N = 59, Sr and Zr nuclei. For N > 59, strongly deformed axially symmetric bands are observed. Recently, a new isomer of half-life 1.4(2) \mu s was observed in 95Kr, the odd--odd 96Rb has been reinvestigated and a new high-spin isomer observed in the even--even 98Zr. These nuclei were studied by means of prompt \gamma -ray spectroscopy of the spontaneous fission of 248Cm using the EUROGAM 2 Ge array and/or measurements of \mu s isomers produced by fission of 239,241Pu with thermal neutrons at the ILL (Grenoble). To allow spectroscopic studies of isomeric states with lifetimes around 100 ns, across a broad range of medium-heavy neutron-rich nuclei, an experiment was performed at a neutron guide of the ILL using thermal-neutron-induced fission. Fission fragments were identified using a small spectrometer consisting of a section to measure time-of-flight and an ionization chamber. Isomeric \gamma rays emitted from complementary fragments were detected in an array of Ge detectors

New isomers and medium-spin structure of the 95Y nucleus

Excited states in 95Y, populated following the spontaneous fission of 248Cm and 252Cf and following fission of 235U induced by thermal neutrons, were studied by means of γ spectroscopy using the EUROGAM2 and GAMMASPHERE multidetector Ge arrays and the LOHENGRIN fission-fragment separator, respectively. We have found a new (17/2−) isomer in 95Y at 3142.2 keV with a half-life of T1/2 = 14.9(5) ns. Another isomer was identified in 95Y at 5022.1 keV and it was assigned a spin-parity (27/2−). For this isomer a half-life of T1/2 = 65(4) ns was determined and four decay branches were found, including an E3 decay. A new E3 decay branch was also found for the known, 1087.5-keV isomer in 95Y, for which we measured a half-life of 51.2(9) μs. The B(E3) and B(E1) transition rates, of 2.0 and 3.8 × 10−7 W.u., respectively, observed in 95Y are significantly lower than in the neighboring 96Zr core, suggesting that octupole correlations in this region are mainly due to the coupling of proton deltaj = 3 orbitals. Shell-model calculations indicate that the (27/2−) isomer in 95Y corresponds to the πg9/2ν(g7/2h11/2) maximally aligned configuration and that all three isomers in 95Y decay, primarily, by M2 transitions between proton g9/2 and f5/2 orbitals

First observation of excited states in the 138^{138}I nucleus

Excited states in the 138I nucleus, including T1/2=1.3 µs isomer decaying by a stretched E2 transition of 68 keV, were observed for the first time. The 138I nucleus was populated in the spontaneous fission of 248Cm and studied by means of prompt gamma-ray spectroscopy using the EUROGAM 2 array. The microsecond isomer was populated in the neutron-induced fission of 235U and observed at the LOHENGRIN separator. Excitation scheme consists of a low-spin part and a medium-spin, DeltaI=1, band based on the 7- state with the (pig7/2nuf7/2)7- dominating configuration, as predicted by the shell model. The shell-model calculations of 138I provide the optimum reproduction of the experimental scheme when the pid5/2 orbital is lowered by 600 keV relative to its position in 133Sb. In the calculation the isomeric level has spin and parity 3- and deexcites by an E2 isomeric transition to the 1- level, located only 9 keV above the predicted 0- ground state. Considering additional information on the ground-state spin from the literature, we propose that in 138I the 1- level corresponds to the ground state and the 0- is located above. We note, however, that additional measurements are required to resolve this problem