The Emission of Short-Range Charged Particles in the Slow Neutron Fission of Uranium

A coincidence counting method has been employed to investigate short-range charged particles produced in the slow neutron fission of ${\mathrm{U}}^{235}$ and ${\mathrm{U}}^{233}$. In the case of ${\mathrm{U}}^{235}$, charged particles with ranges up to 8 mm of air were observed with a frequency of one in 76±8 fissions. The maximum initial specific ionization of these particles was ten times that of $\alpha$-particles from uranium, which suggests that some of the particles have masses considerably greater than that of the $\alpha$-particle. The mass distribution could not be determined from the experimental data. Additional experiments proved that the observed particles were not nuclear recoils produced by fission fragments in their passage through the source and counter gas or fission fragments scattered by the backing material of the source. In the fission of ${\mathrm{U}}^{233}$, particles were observed with ranges up to 7.4 mm of air with an abundance of one in 72±6 fissions.