Excitation energy dependence of the total kinetic energy release in thePu241(He3,αf) reaction

Total fission kinetic energies $E_K$ have been measured as a function of excitation energy in the ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ nucleus excited in the ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$\alpha$) reaction. A small negative slope of $\frac{d{E}_K}{d{E}^{*}}\simeq -0.05\mathrm{}$ is observed in the excitation energy region $E^{*}=5-9\mathrm{}$ MeV. This is substantially smaller than the slope of $\frac{d{E}_K}{d{E}^{*}}=-1.1\mathrm{}$ observed in the ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$($\alpha$,${\alpha }^{\prime }f$) reaction and slightly smaller than the slope of $\frac{d{E}_K}{d{E}^{*}}\simeq -0.35\mathrm{}$ obtained from ($d$,$\mathrm{pf}$) and neutron capture reactions. It is concluded that the primary reaction mechanism plays a decisive role for the total kinetic energy release at near barrier energies but that the angular momentum transfer is not the important parameter. The data are discussed in terms of a simple scission-point model, and in particular the effect of the $Z=50\mathrm{}$, $N=82\mathrm{}$ spherical doubly magic shell in the nascent fragments.