Clustering effects and decay analysis of the light-mass N=Z and N≠Z composite systems formed in heavy ion collisions

Abstract

We investigate the clustering effects in light mass $N=Z$ and $N\ensuremath{\ne}Z$ composite systems $^{20}\mathrm{Ne}^{*}, ^{28}\mathrm{Si}^{*}, ^{40}\mathrm{Ca}^{*}$ and $^{21,22}\mathrm{Ne}^{*}, ^{39}\mathrm{K}^{*}$, respectively, formed in low-energy heavy ion reactions at different excitation energies, within the collective clusterization approach of the dynamical cluster-decay model (DCM) of Gupta and collaborators based on quantum-mechanical fragmentation theory (QMFT). Considering quadrupole deformed and compact orientated nuclei, a comparative decay analysis of these systems has been undertaken for the emission of different intermediate mass fragments (IMFs) or clusters, specifically the IMFs having $Z=3$, 4, and 5 (or $Z=7$, 6, and 5 complimentary fragments from the $^{20}\mathrm{Ne}^{*}$ and $^{21,22}\mathrm{Ne}^{*}$ composite systems) which are having the experimental data available for their $Z$ distribution. Quite interestingly, the QMFT supports clustering in $N=Z$ ($^{20}\mathrm{Ne}^{*}$ and $^{28}\mathrm{Si}^{*}$) and $N\ensuremath{\ne}Z$ ($^{21}\mathrm{Ne}^{*}$ and $^{22}\mathrm{Ne}^{*}$) nuclear systems at excitation energies corresponding to their respective decay threshold or resonant-state energies for the $4\ensuremath{\alpha}, ^{16}\mathrm{O}$ cluster and non-$\ensuremath{\alpha}$ cluster $^{14}\mathrm{C}$ (more so in $^{22}\mathrm{Ne}^{*}\phantom{\rule{4pt}{0ex}}N\ensuremath{\ne}Z$ composite system), supported by the Ikeda diagrams, taking into account the proper pairing strength in the temperature-dependent liquid drop energies. Within the DCM, we notice that at higher excitation energies in addition to $x\ensuremath{\alpha}$-type (where $x$ is an integer) clusters from $N=Z$ composite systems and $xn\ensuremath{-}x\ensuremath{\alpha}$-type clusters from $N\ensuremath{\ne}Z$ composite systems, $np\ensuremath{-}x\ensuremath{\alpha}$-type clusters are relatively quite dominant, with larger preformation probability due to the decreased pairing strength at higher temperatures in the liquid drop energies. Also, the study reveals the presence of competing reaction mechanisms of compound nucleus (fusion-fission, FF) and of noncompound nucleus origin (deep inelastic orbiting, DIO) in the decay of very-light-mass composite systems $^{20,21,22}\mathrm{Ne}^{*}$ and $^{28}\mathrm{Si}^{*}$ at different excitation energies. The DIO contribution in the IMF cross section ${\ensuremath{\sigma}}_{\text{IMF}}$ is extracted for these composite systems, ${\ensuremath{\sigma}}_{\text{IMF}}$ is given as the sum of FF cross section ${\ensuremath{\sigma}}_{\text{FF}}$ and DIO cross section ${\ensuremath{\sigma}}_{\text{DIO}}$. The DCM calculated FF cross sections ${\ensuremath{\sigma}}_{\text{FF}}^{\text{DCM}}$ are in good agreement with the available experimental data.