Precompound emission of light particles in the reactionO16+U238at 20 MeV/nucleon

Abstract

Double differential cross sections have been measured for energetic $p$, $d$, $t$, and $\alpha$ particles emitted in reactions of 315 MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions on ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. In coincidence with light-particle emission, the momentum transfer to the target is determined by measuring the folding angle between the two fission fragments resulting from the sequential decay of the target nucleus. It is concluded that the emission of these particles occurs predominantly in fusionlike "central" collisions and at an early stage of the reaction. The energy and angular distributions are described by thermal emission from a source moving with approximately half of the beam velocity. Alternatively, the energy spectra can be explained by emission from a rotating hot spot. The cross sections for $d$, $t$, and $\alpha$ emission can be described in terms of a generalized form of the coalescence model which takes into account the Coulomb repulsion from the target nucleus.