Long-Range Particles from Nuclear Fission

A measurement of the probability of emission of long-range particles, which are known to be predominantly alpha particles, made with a multiple ionization chamber gave the following results for spontaneous fission: Cf²⁵², 299±{}18; Cm²⁴², 257±{}17; Cm²⁴⁴, 314±{}20; Pu²⁴⁰, 314±{}20; and Pu²⁴², 365±{}29 fissions per long-range particle. The results for thermal neutron-induced fission of the following compound nuclei were: Pu²⁴⁰, 411±{}26; Pu²⁴², 440±{}28; U²³⁶, 449±{}30; and U²³⁴, 414±{}26 fissions per long-range particle and for 1-Mev neutron-induced fission the results were: Pu²⁴⁰, 403±{}25; U²³⁶, 534±{}35; U²³⁵, 466±{}30 fissions per long-range particle. These data indicate a trend of increasing probability of emission of long-range particles with increasing Z²A values and decreasing probability with increasing excitation energy in a given nuclide. Present explanations of these apparently contradictory results seem inadequate.The energy spectra of long-range particles from spontaneous fission of Cf²⁵² and thermal neutron-induced fission of U²³⁵ were observed with a CsI crystal scintillation apparatus and were found to be identical within the accuracy of observations, showing slightly askew bell-shaped distributions with maxima at 17±{}1 Mev and end-point energies of 29±{}1 Mev.