Isoscaling in peripheral nuclear collisions around the Fermi energy and a signal of chemical separation from its excitation energy dependence

The isoscaling is investigated using the fragment yield data from fully reconstructed quasiprojectiles observed in peripheral collisions of ${}^{28}\mathrm{Si}$ with ${}^{124,112}\mathrm{Sn}$ at projectile energies 30 and $50\text{MeV}∕\text{nucleon}$. The excitation energy dependence of the isoscaling parameter ${\beta }^{\prime }$ is observed which is independent of beam energy. For a given quasiprojectile produced in reactions with different targets no isoscaling is observed. The isoscaling thus reflects the level of $N∕Z$ equilibration in reactions with different targets represented by the initial quasiprojectile samples. The excitation energy dependence of the isoscaling parameter ${\beta }^{\prime }$, corrected for the trivial $1∕T$ temperature dependence, does not follow the trend of the homogeneous system above $4\text{MeV}∕\text{nucleon}$ thus possibly signaling the onset of separation into isospin asymmetric dilute and isospin symmetric dense phase.

Figure 1

The isoscaling plots from the reactions of ${}^{28}\mathrm{Si}+{}^{124,112}\mathrm{Sn}$ at $50\text{MeV}∕\text{nucleon}$ for the full set of isotopically resolved quasiprojectiles and for five bins of quasiprojectile excitation energy per nucleon.

Figure 2

As in Fig. 1 but for $30\text{MeV}∕\text{nucleon}$.

Figure 3

The isoscaling plots from the reactions of ${}^{28}\mathrm{Si}+{}^{124,112}\mathrm{Sn}$ at $50\text{MeV}∕\text{nucleon}$ for three reconstructed quasiprojectiles. Symbols as in Figs. 1, 2.

Figure 4

The dependence of observable ${\beta }^{\prime }T$ on relative excitation energy of the quasiprojectile. Open squares and circles show experimental data obtained using the double isotope ratio (a) and $\mathrm{Y}\left({}^3\mathrm{H}\right)∕\mathrm{Y}\left({}^3\mathrm{He}\right)$ slope (b) temperature at 50 and $30\text{MeV}∕\text{nucleon}$, respectively. Full squares represent combined data from both energies. Full and dashed horizontal lines show estimate of ${\beta }^{\prime }T$ obtained when assuming ${\mu }_{p,n}\approx -S_{p,n}$ at 50 and $30\text{MeV}∕\text{nucleon}$, respectively. Solid curve represents the expected trend for homogeneous system. For details see text.