Structure of Nd155 and Gd163 from Cf252 spontaneous fission

Abstract

Background: A puzzle has arisen recently caused by the apparent shift in maximum deformation from the expected $^{66}\mathrm{Dy}$ isotopic chain to the ${}_{60}\mathrm{Nd}$ isotopic chain in the $82lNl126$ and $50lZl82$ midshell region.Purpose: This work provides data for two specific nuclei with odd neutron numbers, $^{155}\mathrm{Nd}$ and $^{163}\mathrm{Gd}$, useful for constraining parameters in models that seek to answer the six proton shift in maximum deformation.Method: Data from the spontaneous fission of $^{252}\mathrm{Cf}$ were taken by the Gammasphere detector array at Lawrence Berkeley National Laboratory to observe the excited states of $^{155}\mathrm{Nd}$ and $^{163}\mathrm{Gd}$.Results: The structure of $^{163}\mathrm{Gd}$ has been expanded with the addition of two new levels and three new $\ensuremath{\gamma}$ rays, which are found to be consistent with previously published calculations and the structure of $^{165}\mathrm{Dy}$. In $^{155}\mathrm{Nd}$, nine new levels and 12 new $\ensuremath{\gamma}$ rays are observed. The spins and parities of the previously known levels in $^{155}\mathrm{Nd}$ have been reassigned from a $\ensuremath{\nu}3/{2}^{\ensuremath{-}}[521]$ ground state configuration to a $\ensuremath{\nu}5/{2}^{+}[642]$ isomeric configuration by comparison of these newly observed levels with levels in $^{153}\mathrm{Nd}$ and $^{155}\mathrm{Sm}$.Conclusion: Further experimentation is required to determine the energy of the newly reassigned $\ensuremath{\nu}5/{2}^{+}[642]$ level in $^{155}\mathrm{Nd}$ with respect to the suspected $\ensuremath{\nu}3/{2}^{\ensuremath{-}}[521]$ ground state. Additionally, more experiments should be conducted to further determine the structure of neutron rich nuclei, rarely produced in the spontaneous fission of $^{252}\mathrm{Cf}$, such as $^{163}\mathrm{Gd}$.