Analysis of the decay of the rare p nucleus Te*120 within a collective clusterization approach

Abstract

The dynamics of one out of thirty-five known rare $p$ nuclei, i.e., the $^{120}\mathrm{Te}^{*}$ compound nucleus (CN), are worked out within the dynamical cluster-decay model (DCM) over incident $\ensuremath{\alpha}$-beam energies ${E}_{\ensuremath{\alpha}}\ensuremath{\approx}10.3$ to 30 MeV, constituting energies below, around, and above the Coulomb barrier. Experimental data are available for the decay of the $^{120}\mathrm{Te}^{*}$ CN formed in the $^{4}\mathrm{He}+^{116}\mathrm{Sn}$ reaction, to both ground $(g)$ and metastable $(m)$ states where the predominant decay mode is neutron emission $xn$ $(x=1,2)$, essentially a ``cold-fusion'' reaction. Both kinds of decays are independently addressed here, optimizing the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$, the model's only parameter, to best fit the data for observed $xn$, $x=1$ or 2, channel cross sections while simultaneously predicting cross sections for other experimentally unobserved channels. The collective clusterization technique of the DCM involves a two step mechanism for analyzing a CN decay: first the preformation of the fragments within the parent CN and then the penetration of the preformed clusters through their respective interaction potential barriers, with probabilities ${P}_{0}$ and $P$, respectively. The quadrupole deformations of nuclei $({\ensuremath{\beta}}_{2i})$ with their respective ``optimum'' orientations ${\ensuremath{\theta}}_{i}^{\mathrm{opt}.}$ and coplanarity $(\mathrm{\ensuremath{\Phi}}={0}^{\ensuremath{\circ}})$, are included for the use of ``cold-elongated'' configurations. Interestingly, in complete agreement with experimental observations, the results of the theoretical model calculations require incorporation of significant quasifissionlike (qf-like) noncompound nucleus (nCN) effects above ${E}_{\ensuremath{\alpha}}\ensuremath{\approx}20$ MeV, corresponding to decay of $^{120}\mathrm{Te}^{*}$ to the ground state of $^{118}\mathrm{Te}$ via $2n$. Decay of $^{120}\mathrm{Te}^{*}$ to the metastable state $^{119m}\mathrm{Te}$ via $1n$ is a pure CN decay over the entire energy range studied here. The smooth variation of $\mathrm{\ensuremath{\Delta}}R$ values with CN excitation energy ${E}_{CN}^{*}$ is also well within the nuclear proximity limit of $\ensuremath{\approx}2.5\phantom{\rule{4pt}{0ex}}\text{fm}$. The trends of statistical CN formation probability and survival probability, ${P}_{CN}$ and ${P}_{\mathrm{surv}}$, respectively, with ${E}_{CN}^{*}$ match the known systematic of other compound nuclei of mass range $100l{A}_{CN}⪅200$ and ${Z}_{1}{Z}_{2}l460$ studied so far within the model, which gives further credence to the calculations.