Study of the Levels inLa140Using theLa

Abstract

The levels in 4 La have been studied following thermal-neutron capture in La using Ge(Li), Si(Li), curved-crystal, and coincidence spectrometers. The neutron binding energy of La was determined as 5161. 1 +1.0 keV. The data, when combined with the previous ' 9La-(d, p)" La study, allow the assignment of the first 14 states up to 581.060 keV to the mixed configurations kg»2 vfv&2 and md&&2vf7~2. The energies of states in keV (spin parity) are: 0 (3 ), 29.965 060 (0 ). Comparisons of p-ray branching ratios and (d, p) cross sections with the predictions of a quasiparticle model for odd-odd nuclei allow a relatively uncompromised solution for the state vectors for the first 14 states. The success of this model implies that there is little phonon or fourquasiparticle admixture through the level at 581.060 keV. A detailed experimental study of additional levels up to 1055 keV has been performed.

Radiative-capture cross sections for the La139(n,γ) reaction using thermal neutrons and structural properties of LaHurst1, Sweet2, Goldblum3 et al. 2019Phys. Rev. C3000View full textAdd to dashboardCite

“…It is also consistent with the earlier observation in Ref. [34] assuming their correction factor for γ-ray self absorption.…”

“…The 139 La(n, γ) reaction populates many levels based on several possible configurations above the Z = 50 and N = 82 shell closures. The low-lying levels in the residual nucleus are well characterized in terms of quasiparticle couplings between valence protons in the 1g 7/2 and 2d 5/2 orbits with neutrons in the 2f 7/2 and 3p 3/2 orbits [33,34]. Earlier theoretical work suggests these negative-parity states involve the protonneutron multiplets |π(l jp ) ⊗ ν(l jn ); |j p − j n | .…”

“…, 6 − Because we are suggesting a J π = 5 − assignment for the 103.8-keV level and the other 5 − assignment is already exhausted through the 34.6-keV level, this leaves a 6 − assignment as the only remaining possibility from the above octuplet and sextuplet of levels, with the other 6 − assignment occupied by the 48.9-keV level. Particlephonon coupling is demonstrably unimportant at such low excitation energies in 140 La [34], and the ν(3p 3/2 ) orbital is unlikely to play a significant role through fourquasiparticle admixtures in this regime. Furthermore, a 6 − level cannot be generated by coupling quasiparticles in the ν(3p 3/2 ) orbital with those in the available proton orbitals.…”

“…IV A, we may impose ranges of permissible J π assignments to levels fed by primary γ rays. And because we expect dipole and quadrupole transitions to dominate the secondary component of the γ-decay scheme [34,75], we may then use decay properties of the associated intermediate and final levels to further constrain the range of J π values or even deduce unique solutions in some cases. Assignments deduced using these methodologies are flagged for several levels in Table V and a summary of the important findings is discussed below.…”

“…A (2 − ) assignment is proposed in Ref. [34] on the basis of deexcitation γ rays feeding 0 − , 2 − , and 3 − levels. However, the authors acknowledge a lack of supporting evidence from a coincidence measurement and the transition to the 0 − level has been reported in ENSDF with uncertain placement [3].…”