Cluster formation in neutron-rich Be and B isotopes

Abstract

Evaluating the formation of clusters in finite and infinite nuclear systems is a fundamental problem in nuclear physics, and the variation in clustering in the isotope chain up to the neutron drip-line is one such intriguing phenomenon. Recently, experiments performed using the (p, pα) reactions have revealed a negative correlation between α-cluster formation and neutron number in Sn isotopes, showing a trend opposite to that theoretically predicted for Be and B isotopes. Although the observed charge radii of the Be and B isotopes suggest the formation of clusters as the neutron drip-line is approached, these radii themselves are not a physical quantity that can directly probe the cluster structure. Here, we directly investigate the cluster formation in Be and B isotopes to elucidate the possibility of clustering as the neutron drip-line is approached. It has been shown that the sum of the S-factors (i.e., S(α), S(⁶He), and S(⁸He)) increases as the neutron drip-line approaches, in agreement with those of previous studies. The results indicate that the excess neutrons contribute to the formation of ⁶He and ⁸He clusters as well as α clusters. Thus, S(α) is not sufficient to estimate the enhancement of clustering in Be and B isotopes.