$N$ and $Z$ odd-even staggering in Kr+Sn collisions at Fermi energies

The odd-even staggering of the yield of final reaction products has been studied as a function of proton ($Z$) and neutron $\left(N\right)$ numbers for the collisions ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$ and ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ at 35 MeV/nucleon in a wide range of elements (up to $Z\approx 20$). The experimental data show that staggering effects rapidly decrease with increasing size of the fragments. Moreover the staggering in $N$ is definitely larger than the one in $Z$. Similar general features are qualitatively reproduced by the gemini code. Concerning the comparison of the two systems, the staggering in $N$ is in general rather similar, being slightly larger only for the lightest fragments produced in the $n$-rich system. In contrast the staggering in $Z$, although smaller than that in $N$, is sizably larger for the $n$-poor system with respect to the $n$-rich one.

Figure 1

Experimental $Z$ distributions for the systems (a) ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ and (b) ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$, both at 35 MeV/nucleon. Staggering as a function of $Z$, highlighted by the ratio $R\left(Z\right)$ for the same systems (c) ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ and (d) ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$. Bars indicate statistical errors.

Figure 2

Experimental $N$ distributions for the systems (a) ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ and (b) ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$, both at 35 MeV/nucleon. Staggering as a function of $N$, highlighted by the ratio $R\left(N\right)$ for the same systems (c) ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ and (d) ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$. Bars indicate statistical errors.

Figure 3

Parameter $\delta$ as a function (a) of $Z$ and (b) of $N$ for final fragments in the collisions ${}^{84}\mathrm{Kr}+{}^{112}\mathrm{Sn}$ (solid symbols) and ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$ (open symbols). Bars indicate statistical errors.

Figure 4

Parameter $\delta$ for the staggering in $Z$ (a) and $N$ (b) from gemini simulations of the decay ${}^{84}$Kr (solid squares) or ${}^{74}$Ge (solid circles) at 2.7 MeV/nucleon of excitation energy.

Figure 5

Parameter $\delta$ from the experimental data of the reaction ${}^{84}\mathrm{Kr}+{}^{124}\mathrm{Sn}$, plotted as a function of $Z$ for even (a) and odd (b) chains of neutron excess $N-Z$ and as a function of $N$, again for even (c) and odd (d) chains of $N-Z$. Note the larger vertical scale with respect to Fig. 3.