Experimental studies of the two-step scheme with an intense radioactive Sn132 beam for next-generation production of very neutron-rich nuclei

Abstract

The study of nuclei in the yet-unexplored, very neutron-rich, mid- to heavy-mass region of the nuclear chart, comprising perhaps half of all nuclei predicted to exist, is leading to new and/or upgraded facilities, as well as to research into the underlying production processes. In the present study, the usefulness of the two-step scheme, an alternate method to produce very neutron-rich nuclei, by a combination of an isotope-separation online (ISOL) system as a first step, and in-beam fragmentation of re-accelerated radioactive isotopes (RIs) as a second step, was investigated with a $^{132}\mathrm{Sn}$ beam. Very neutron-rich RIs around the neutron-rich neutron number $N=82$ region were produced from the 278-MeV/nucleon $^{132}\mathrm{Sn}$ beam impinging on a 5.97-mm Be target, and their production cross sections were measured. Yields were then estimated for the two-step scheme with the $^{132}\mathrm{Sn}$ beam relative to the ones by a one-step scheme, in-flight fission of a $^{238}\mathrm{U}$ beam, for 1-MW proton and $^{238}\mathrm{U}$ beams at respective RI-beam facilities. This comparison suggests that the two-step scheme with the $^{132}\mathrm{Sn}$ beam provides yields $>40$-times higher than those with the one-step scheme for the very neutron-rich $N=82$ region. Moreover, by using various RI beams over the nuclear chart from ISOL, certain kinds of very neutron-rich RIs around the supernova $r$-process path can be produced with greater yields than by the one-step approach.