Production of fragments with more neutrons than the projectile at intermediate energies

The nuclear reaction mechanism leading to the production of fragments with more neutrons than the projectile at intermediate energies is studied. A large enhancement in the production of these fragments is observed in the reactions with less neutron-rich projectiles or neutron-rich targets. This enhancement would be related to the difference of the neutron density at the nuclei surface as a factor influencing the process of nucleon exchange in peripheral collisions. From a practical viewpoint, such a nuclear reaction mechanism could provide a novel synthetic avenue to access extremely neutron-rich isotopes towards the neutron drip line.

Figure 1

Longitudinal momentum distribution peaks of the fragments with neutron number $N_f=N_p+1$ (a) and $N_f=N_p+2$ (b).

Figure 2

Production cross sections of the fragments with neutron number $N_f=N_p+1$ (a) and $N_f=N_p+2$ (b).

Figure 3

Neutron density distributions (a) and the ratios between neutron and proton densities (b) calculated with the HIPSE model. The solid curves in (a) are the fit results by using Eq. (1).

Figure 4

Production cross sections for $N_f=29$ (a) and $N_f=30$ (b) isotones. The experimental cross sections in the reaction ${}^{48}\mathrm{Ca}{+}^9\text{Be}$ at 140 MeV/nucleon [20] are shown by solid circles. Open circles, open squares, and open triangles represent the results of fragmentation of ${}^{54}\mathrm{Cr},{}^{56}\mathrm{Fe}$, and ${}^{64}\mathrm{Ni}$ projectiles in a ${}^{238}\mathrm{U}$ target calculated with the EPAX 3 model.