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

Abstract

Double-differential emission probabilities P(E, 0) in angle 0 and energy E of protons, tritons, and e-particles were measured in the case of spontaneous fission of 252Cf. A detector system consisting of position-sensitive parallel-plate avalanche counters (PPAC) and A E--Etelescopes 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 e-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)-collisions. Unlike for tritons and e-particles the P(E, 0) 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 for e-particles completely fails. Upper limits for an additional scission component of proton emission are given.

Isotopic equilibrium constants for very low-density and low-temperature nuclear matter

“…In reference [13] He yields [21,22,[35][36][37][38][39][40][41][42][43][44]. References are the primary sources.…”

Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission

“…These previous efforts have treated the problem by emphasizing the dominance of one of the following: neck instabilities and rupture [14], barrier penetration of pre-formed clusters [15] or formation of fragments from interacting nucleons in the fission neck region [12]. However, these models have had only limited success and have been unable to explain such key experimental results as the high yield of scission tritons relative to scission protons [1,2,16] and the non-observation of 3 He [1,2,8,9]. Recently, Lestone proposed a model in which a statistical evaporation of the ternary particle is moderated by time dependent emission barriers which evolve as the fissioning nucleus approaches the scission point [15].…”