Sn118levels studied by theSn120(p,t) reaction: High-resolution measurements, shell model, and distorted-wave Born approximation calculations

Abstract

Cross-section angular distributions of 38 ($p$, $t$) transitions to final states of $^{118}\mathrm{Sn}$ up to an excitation energy of 3.597 MeV have been measured in a high-resolution experiment at an incident proton energy of 21 MeV. A distorted-wave Born approximation (DWBA) analysis of the 38 experimental differential cross sections, carried out by using conventional Woods-Saxon potentials, allowed us either 18 confirmations of previous spin and parity values or new assignments of spin and parity to 14 states of $^{118}\mathrm{Sn}$. A shell-model calculation has been performed by using a realistic two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential. The doubly-magic nucleus $^{132}\mathrm{Sn}$ is assumed as a closed core, with 14 valence neutron holes occupying the five levels of the 50--82 shell. Within this model space the calculations are performed by employing the seniority scheme including states with seniority up to 4. The energy spectrum of $^{118}\mathrm{Sn}$ has been calculated and compared with the experimental one. The theoretical two-neutron spectroscopic amplitudes are used in the microscopic DWBA calculations of some cross-section angular distributions.