Enhanced Production of Neutron-Rich Rare Isotopes in Peripheral Collisions at Fermi Energies

A large enhancement in the production of neutron-rich projectile residues is observed in the reactions of a $25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}$ ${}^{86}\mathrm{K}\mathrm{r}$ beam with the neutron-rich ${}^{124}\mathrm{S}\mathrm{n}$ and ${}^{64}\mathrm{N}\mathrm{i}$ targets relative to the predictions of the EPAX parametrization of high-energy fragmentation, as well as relative to the reaction with the less neutron-rich ${}^{112}\mathrm{S}\mathrm{n}$ target. A hybrid model based on a deep-inelastic transfer (DIT) code followed by a statistical deexcitation code accounts for part of the observed large cross sections. The DIT simulation indicates that the production of neutron-rich nuclides in these reactions is associated with peripheral nucleon exchange in which the neutron skins of the neutron-rich ${}^{124}\mathrm{S}\mathrm{n}$ and ${}^{64}\mathrm{N}\mathrm{i}$ target nuclei may play an important role. From a practical viewpoint, such reactions offer a novel synthetic avenue to access extremely neutron-rich rare isotopes towards the neutron-drip line.

Figure 1

Mass distributions of elements $Z=30–35$ from the reaction of ${}^{86}\mathrm{K}\mathrm{r}$ ($25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}$) with ${}^{124}\mathrm{S}\mathrm{n}$ and ${}^{112}\mathrm{S}\mathrm{n}$. The data are shown by full circles for ${}^{86}\mathrm{K}\mathrm{r}+{}^{124}\mathrm{S}\mathrm{n}$ and full squares for ${}^{86}\mathrm{K}\mathrm{r}+{}^{112}\mathrm{S}\mathrm{n}$. The dotted lines are EPAX expectations [14].

Figure 2

Ratio of measured cross sections of projectile residues from ${}^{86}\mathrm{K}\mathrm{r}$ ($25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}$) on ${}^{124}\mathrm{S}\mathrm{n}$ target (a) (current measurement), and on ${}^{64}\mathrm{N}\mathrm{i}$ target (b) [23] with respect to EPAX expectations [14]. Arrows indicate the $N/Z$ of the projectile.

Figure 3

Comparison of experimental mass distributions of Se ($Z=34$), Ge ($Z=32$), and Zn ($Z=30$) from ${}^{86}\mathrm{K}\mathrm{r}$ ($25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}$) on ${}^{64}\mathrm{N}\mathrm{i}$ [23], ${}^{124}\mathrm{S}\mathrm{n}$, and ${}^{112}\mathrm{S}\mathrm{n}$ (present data) with DIT/GEMINI calculations without (thick solid line) and with (thick dashed line) neutron and proton density distributions. The thin solid line is the EPAX prediction [14].