First identification of collective bands and octupole correlations in the neutron-richLa143nucleus

Abstract

The high-spin levels in the neutron-rich 143 La nucleus have been investigated from the study of prompt γ rays in the spontaneous fission of 252 Cf with the Gammasphere detector array. A new level scheme with spin up to 27/2h has been established, and the collective bands have been identified for the first time. A set of opposite-parity bands connected by I = 1E1 crossing transitions gives evidence for octupole correlations. The results of B(E1)/B(E2) branching ratios indicate that the octupole correlations in 143 La are strong. The reflection-asymmetry shell model is applied to calculate the levels of the octupole bands of 143 La, and the calculated results are in good agreement with the experimental ones.

$^{145}$Ba and $^{145, 146}$La structure from lifetime measurements

“…Similar studies have been performed for the lanthanum Z=57 isotopes. Fission experiments found alternating-parity bands at intermediate and high spins for 143,145,147 La, but the non-observation of parity doublets for the ground state prevented the establishment of permanent octupole deformation [16][17][18][19]. As is common in nuclear physics, odd-odd nuclei are typically less well studied than their even-even or odd-A neighbours.…”