Medium-spin levels and A 360 ns isomer in the N = 80 nucleus 137La

High spin spectroscopy of 137La

“…The TDC (Time-to-Digital Converter) time range was set to 800 ns so that it was also possible to acquire delayed events. In earlier in-beam experiments [6,7], the states above the 360 ns 19 2 − isomer at 1869.9 keV, in 137 La, were not much seen and also the data suffered due to statistics. Due to higher efficiency of our array, both doubles as well as triples coincidence events could be gathered separately with reasonable statistics.…”

“…The authors of Ref. [7] identified a T 1/2 = 360 ± 40 ns isomer at 1869.9 keV and spin 19 2 − and placed an upper limit of T 1/2 1.5 ns for the other levels above the 360 ns isomer, observed in their experiment. After our work was completed, we came across an unpublished report by Rizzutto et al [8] who used the same reaction at E beam = 49 MeV and attempted to extend the level scheme above the 360 ns isomer using four HPGe detectors and a 7 element NaI(Tl) multiplicity filter.…”

“…Kortelahti et al [7], in an attempt to interpret their results, used the triaxial rotor-plus-particle model of Meyer-ter-Vehn [9] and found that the observed negative parity sequence up to 15 2 − could be reproduced by using an oblate triaxial shape (γ > 30 • ). Alonso et al [10] and Aryaeinejad et al [11] applied the interacting-boson-fermion-approximation (IBFA) model for odd-mass Ba and La isotopes and odd-mass N = 80 isotones, respectively.…”

“…The low lying level structure of 137 La has been studied earlier by using the reactions 130 Te( 11 B, 4n) 137 La [6] and 138 Ba(p, 2n) 137 La [7]. Of these, Leigh et al [6] were interested in the systematics of low lying excitations in odd-A La isotopes whereas Kortelahti et al [7] developed the level scheme of 137 La up to a moderate excitation energy of 2.337 MeV and spin.…”

“…Of these, Leigh et al [6] were interested in the systematics of low lying excitations in odd-A La isotopes whereas Kortelahti et al [7] developed the level scheme of 137 La up to a moderate excitation energy of 2.337 MeV and spin. In the latter work [7], two HPGe detectors and one Ge(Li) detector was used for γ γ coincidence measurements and spin-parity assignments were done by measuring conversion electron and γ ray angular distribution. The authors of Ref.…”