High-spin states inLa136and possible structure change in theN=79region

Abstract

High-spin states in the odd-odd nucleus 136 La, which is located close to the β-stability line, have been investigated in the radioactive-beam-induced fusion-evaporation reaction 124 Sn( 17 N,5n). The use of the radioactive beam enabled a highly sensitive and successful search for a new isomer [14 + , T 1/2 = 187 (27) ns] in 136 La. In the A = 130-140 mass region, no such long-lived isomer has been observed at high spin in odd-odd nuclei. The 136 La level scheme was revised, incorporating the 14 + isomer and six new levels. The results were compared with pair-truncated shell model (PTSM) calculations which successfully explain the level structure of the πh 11/2 ⊗ νh −1 11/2 bands in 132 La and 134 La. The isomerism of the 14 + state was investigated also by a collective model, the cranked Nilsson-Strutinsky (CNS) model, which explains various high-spin structures in the medium-heavy mass region. It is suggested that a new type of collective structure is induced in the PTSM model by the increase of the number of πg 7/2 pairs, and/or in the CNS model by the configuration change associated with the shape change in 136 La.

Structure of the11/2−isomeric state inLa133

“…The level structures of nuclei evolve from single particle to collective nature, as one goes away from the Z = 50 and N = 82 shell gaps. The transitional nuclei around A ∼ 135 with Z > 50 and N < 82 lie between the spherical and deformed regions and show complex and rich level structures due to interplay for single-particle and collective excitation modes [1][2][3]. Occupation of high-j orbitals for protons and neutrons plays a crucial role for various structure phenomena for nuclei in this region, such as signature splitting, signature inversion, magnetic rotation, wobbling motion, chiral rotation and high-spin isomers.…”

“…The electromagnetic moment measurements of the isomers in these nuclei are of particular interest, as they provide a stringent test of the LSSM calculations. Recently, the isomers in 135,136 La isotopes have attracted lot of attention [3,5,6]. As a part of a systematic study of the isomers in this region, we have performed experiments to measure the g-factor of the well-known 11/2 − isomer in 133 La isotope and compare the results with the LSSM calculations.…”

Nuclear matrix elements of neutrinoless double beta decay for masses 130 and 136 in the shell model

“…For example, isomers with spin-parity 10 + are systematically present in even-even Sn isotopes [15]. Recently, new isomeric states have been found in 135 La [16] and 136 La [17], but the nature of those isomers still needs to be unveiled. These isomeric states in this mass region were systematically analyzed in the nuclear shell model (SM) [18,19].…”