Light charged particle release in252Cf spontaneous fission: Tripartition versus fragment de-excitation

Abstract

Double-differential emission probabilities P (E, θ) in angle θ and energy E of protons, tritons, and α-particles were measured in the case of spontaneous fission of252Cf. A detector system consisting of position-sensitive parallel-plate avalanche counters (PPAC) and ΔE−E-telescopes allowed a coincidence measurement of fission fragments (FF) and light charged particles (LCP) in the whole region from 0 deg. to 180 deg. with respect to the light-fragment direction. Previous results for α-particle emission were confirmed. The background contributions for protons are discussed in detail. For proton emission the background arising from (n, p)-reactions was measured and compared with a corresponding Monte-Carlo simulation of elastic (n, p)-clusions. Unlike for tritons and a-particles the P (E, θ) distribution for protons does not show equatorial peaking in 0 between 80 deg. and 90 deg. and contradicts classical scission point emission. The proton distribution, however, agrees with fragment de-excitation calculations in the framework of the cascade evaporation model (CEM) whereas an analogous calculation forα-particles completely fails. Upper limits for an additional scission component of proton emission are given.