Y. Fang

Nuclear structure and β -decay schemes for Te nuclides beyond N=82

We study for the first time the internal structure of 140Te through the beta-delayed gamma-ray spectroscopy of 140Sb. The very neutron-rich 140Sb, Z = 51 and N = 89, ions were produced by the in-flight fission of 238U beam on a 9Be target at 345 MeV per nucleon at the Radioactive Ion Beam Factory, RIKEN. The half-life and spin-parity of 140Sb are reported as 124(30) ms and (4-), respectively. In addition to the excited states of 140Te produced by the beta-decay branch, the beta-delayed one-neutron and two-neutron emission branches were also established. By identifying the first 2+ and 4+ excited states of 140Te, we found that Te isotopes persist their vibrator character with E(4+)/E(2+) = 2. We discuss the distinctive features manifest in this region, such as valence neutron symmetry and asymmetry, revealed in pairs of isotopes with the same neutron holes and particles with respect to N = 82.

New Isotopes and Proton Emitters Crossing the Drip Line in the Vicinity of

Several new isotopes, ^{96}In, ^{94}Cd, ^{92}Ag, and ^{90}Pd, have been identified at the RIKEN Nishina Center. The study of proton drip-line nuclei in the vicinity of ^{100}Sn led to the discovery of new proton emitters ^{93}Ag and ^{89}Rh with half-lives in the submicrosecond range. The systematics of the half-lives of odd-Z nuclei with T_{z}=-1/2 toward ^{99}Sn shows a stabilizing effect of the Z=50 shell closure. Production cross sections for nuclei in the vicinity of ^{100}Sn measured at different energies and target thicknesses were compared to the cross sections calculated by epax taking into account contributions of secondary reactions in the primary target.

^{100}

F. Browne et al.; 4 pags.; 2 figs.; Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 31–September 7, 2014; PACS numbers: 21.10.Re, 21.10.Tg, 23.20.Js, 27.60.+j

Sn

Abstract The low-lying structures of the midshell ν g 9 / 2 Ni isotopes 72Ni and 74Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following β decay of the mother nuclei 72Co and 74Co. As a result, we provide a complete picture in terms of the seniority scheme up to the first ( 8 + ) levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron g 9 / 2 shell. We find that the disappearance of the seniority isomerism in the ( 8 1 + ) states can be explained by a lowering of the seniority-four ( 6 + ) levels as predicted years ago. For 74Ni, the internal de-excitation pattern of the newly observed ( 6 2 + ) state supports a restoration of the normal seniority ordering up to spin J = 4 . This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near 78Ni.

GAMMA-RAY SPECTROSCOPY IN THE VICINITY OF 108 Zr

A new isomer with ms half-life was observed in 160Nd at RIBF, RIKEN Nishina Center by using in-flight fission of 238U beam and a cluster-type Ge detector array, EURICA. The experimental results and a PSM calculation indicate that the isomer in 160Nd is a 2 quasi-particle excitation of nneutrons with a configuration of n1/2[521]x7/2[633] as the case in other N = 100 isotones. The E(4+)/E(2+) ratio of the ground-state band, 3.29, shows the 160Nd is well deformed and the ground band has a rotational nature. The 4- excitation of 160Nd showed an increase in energy byx18 100 keV compared to that of 162Sm as predicted by the PSM calculation. A PSM calculation was performed by changing input beta_4 value and confirmed that the large hexadecupole deformation in Nd was responsible for the increase of the isomer energy.