Investigation of Shell Model States in Exotic Odd-A Sb Isotopes

Abstract

The level structures of 134Sb and 135Sb were studied in the b- decays of the very-neutron-rich 134,135Sn isotopes. Tin isotopes were produced by proton- or neutron-induced fission at CERN/ISOLDE and ionized using a resonance ionization laser ion source. Following mass separation of the Sn nuclei, it was possible to collect g-ray singles and g-g coincidence data as a function of time for the decays of 134Sn and 135Sn. From these data, the position of the 7- b-decaying isomer in 134Sb has been established at 279 keV, and the 5- and 6- members of the f7/2g7/2 multiplet in 134Sb have also been identified, along with three new 1- levels at higher energy.

New structure information was also obtained for 135Sb. New important levels in 135Sb were established at 282, 440, and 798 keV, which are given tentative spin and parity assignments of 5/2+, 3/2+ and 9/2+, respectively. The level structures of both 134Sb and 135Sb were compared with shell model calculations.

Following b-delayed neutron decay of the parents, half-lives (T1/2) for 135,136,137Sn were measured to be 530(10) ms, 300(15) ms, and 250(30) ms, respectively. The corresponding b-delayed neutron probabilities (Pn) for these nuclides were measured to be 20(2)%, 27(4)%, and 33(12)%, for 135,136,137Sn decay. Limited data indicated an upper limit of 150 ms for the T1/2 of 138Sn.

Low-spin levels in 111Sb and 113Sb were identified at Argonne National Laboratory following the b+/EC decay of 111Te and 113Te, respectively. 111Te and 113Te were produced and separated by the Fragment Mass Analyzer via the 56Fe(58,60Ni,2pn)111,113Te reactions. Analysis of the g-singles, g-g coincidence, and g-time data resulted in the identification of new levels in 111Sb, including levels at 487 and 881 keV that have been tentatively assigned spins and parities of 1/2+ and 3/2+, respectively. In addition, a more precise T1/2 for 111Te decay was measured from the decay of the two most intense g transitions to be 26.2(6) s. The positions of these new levels were compared with shell model calculations for the odd-A Sb isotopes from A = 105 to A = 111.

Several new g rays and levels in 113Sb were identified, with data supporting a 3/2+ and 7/2+ assignment for the previously ambiguous 1019- and 1181-keV levels, respectively. Identification of the spins and parities of these states suggest a 5/2+ assignment for the ground state of 113Te.