Emerging collectivity from the nuclear structure of Xe132 : Inelastic neutron scattering studies and shell-model calculations

Abstract

Inelastic neutron scattering was used to study the low-lying nuclear structure of 132 Xe. A comprehensive level scheme is presented, as well as new level lifetimes, multipole mixing ratios, branching ratios, and transition probabilities. Comparisons of these data as well as previously measured E2 strengths and g factors are made with new shell-model calculations for 132,134,136 Xe to explore the emergence of collectivity in the Xe isotopes with N < 82 near the closed shell. *

Spectroscopy of states in $^{136}\rm{Ba}$ using the $^{138}\rm{Ba}(p,t)$ reaction

“…E x = 3108.7 keV: The NDS lists a 2 + state at 3109.59 (9) keV. The measured angular distribution for our observed peak corresponding to this state agrees well with a combination of L = 0 and L = 2 transitions.…”

“…E x = 3498.7 keV: There are no reported levels at this energy. The nearest states listed in the NDS are at 3505.5 (9) and 3508.7(3) keV, with J π = 0 (+) , 1, 2, 3 + and J π = (4 + ) respectively [31]. Our measured angular distribution for this level is consistent with both L = 4 and L = 5 transfer.…”

“…There has been significant interest in studying the structure of nuclei in Xe-Ba-Ce region of the Segrè chart [1][2][3][4][5][6][7][8], with particular emphasis on the A ∼ 130 shape-transitional isotopes [9][10][11][12][13][14][15]. In this context, 136 Ba (with neutron number N = 80) is an interesting case.…”

To Shell Model, or Not to Shell Model, That Is the Question

“…In such cases, the observed transition strengths result from small components of the wavefunction, which can lead to considerable variations in the shell model predictions, despite the calculations agreeing on the dominant structure of the states. It was noted in [32] that the large-basis shell model calculations support the dominant configurations assigned in the (1g 7/2 2d 5/2 ) seniority model up to the 4 + 2 state at 2.1 MeV excitation, although there is considerable configuration mixing. The (1g 7/2 2d 5/2 ) model accounts for all states up to about 2.8 MeV, with the exception of the 0 + 2 state (more on the 0 + 2 state below in this Section).…”

“…However, shell model calculations affirm the dominant seniority structures. The case of 136 Xe has been studied comprehensively [30,32]. Table 1 shows experimental B(E2) values between low-excitation states in 136 Xe in comparison to the (1g 7/2 2d 5/2 ) seniority model, as well as several shell model calculations that include all orbits in the 50 ≤ Z ≤ 82 major shell but use alternative interactions.…”