Temperature of low-energy ternary fission from the dependence of particle yields on the mass of the fissioning system

In thermal neutron-induced and spontaneous fission the addition of two neutrons to a neutron-even system produces only minor changes to the shape, kinetic energy, and temperature of the scission configuration. If these changes are assumed negligible and if ternary fission is associated with a statistical process then the ratio of ternary fission yields for systems differing by two atomic mass units can be used to infer a nuclear temperature. The yields of hydrogen, helium, lithium, and beryllium isotopes ejected perpendicular to the direction of the main fragments from ^233,235U(n_th,f), ^239,241Pu(n_th,f), and ^250,252Cf spontaneous fission give a nuclear temperature T=1.24±0.10 MeV. The yield of polar α particles from ^233,235U(n_th,f) give T=1.13±0.24 MeV. These results are in agreement with other inferred low-energy ternary fission temperatures and support the idea that both equatorial and polar ternary fission involve a statistical process where the ejected particles are in equilibrium with a heat bath with a temperature slightly hotter than 1 MeV.