α -decay chains of the superheavy nuclei Rg255–350

Abstract

The decay modes and half-lives of 96 isotopes of the superheavy element roentgenium (Rg) within the range of $255\ensuremath{\le}A\ensuremath{\le}350$ come under investigation in the present paper. The isotopes which lie beyond the proton drip line are identified by calculating the one-proton and two-proton separation energies. The $\ensuremath{\alpha}$-decay half-lives are calculated using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). For a theoretical comparison the $\ensuremath{\alpha}$ half-lives are also evaluated using the Viola-Seaborg semiempirical relation, the universal curve of Poenaru et al., the analytical formula of Royer, and the universal decay law of Qi et al. Spontaneous fission half-lives are computed with the shell-effect-dependent formula of Santhosh and Nithya and the semiempirical formula of Xu et al. The decay modes are predicted by comparing the $\ensuremath{\alpha}$-decay half-lives within the CPPMDN with the corresponding spontaneous fission half-lives computed by the shell-effect-dependent formula of Santhosh and Nithya. In our paper it is seen that the isotopes $^{255\text{--}271,273}\mathrm{Rg}$ lie beyond the proton drip line and hence decay through proton emission. The isotopes $^{272,274\text{--}277}\mathrm{Rg}$ exhibit long $\ensuremath{\alpha}$ chains. Three $\ensuremath{\alpha}$ chains are predicted from the isotopes $^{278\text{--}282}\mathrm{Rg}$. The isotopes $^{283\text{--}345}\mathrm{Rg}$ decay through spontaneous fission. The isotopes $^{346\text{--}350}\mathrm{Rg}$ are found to be stable against $\ensuremath{\alpha}$ decay. The theoretical results are compared with the available experimental results and are seen to be matching well. We hope that our predictions will be useful in future experimental investigations.