Cross sections for the production of shell-stabilized evaporation residues in the ${}^{50}\mathrm{Ti}+{}^{160}\text{Gd}, {}^{159}\mathrm{Tb}, {}^{162}\mathrm{Dy}$, and ${}^{54}\mathrm{Cr}+{}^{162}\text{Dy}$ reactions are reported. The compound nucleus excitation energy range considered principally covers the $4n$ evaporation channel with segments of the $3n$ and $5n$ channels also measured. The resultant production cross sections are for nuclides with $Z=86-90$. From an analysis based on a statistical model, it is concluded that a larger fission probability than that predicted by the Bohr-Wheeler transition-state theory is needed to describe the data. This outcome is attributed to the influence of collective nuclear excitations. Subsequently, the expected stability enhancement against fission due to the influence of the magic $N=126$ shell is not evident. The $xn$ excitation functions measured in previous experiments in the reactions ${}^{48}\mathrm{Ca}+{}^{154}\text{Gd}, {}^{159}\mathrm{Tb},{}^{162}\text{Dy}$, and ${}^{165}\mathrm{Ho}$ are combined with the present data for $Z>20$ projectiles to illustrate systematic behavior of measured cross sections as a function of the difference in fission barrier and neutron separation energy.

• Received 19 May 2015
• Revised 21 August 2015

DOI:https://doi.org/10.1103/PhysRevC.92.054601