Characteristics of Symmetric and Asymmetric Fission Modes as a Function of the Compound Nucleus Excitation in the Proton-Induced Fission of $^{233}$Pa, $^{239}$Np and $^{243}$Am
Résumé
Average preequilibrium $\langle M_n^{preeq}\rangle$ average statistical prescission $\langle M_n^{stpre}\rangle$ and postscission $\langle M_n^{post}\rangle$ neutron multiplicities as well as average gamma-ray multiplicity $\langle M_{gamma}\rangle$, average energy emitted by gamma-rays $\langle E_{gamma}\rangle$ and average energy per one gamma quantum $\langle\varepsilon_{gamma}\rangle$ as a function of mass and total kinetic energy (TKE) of fission fragments were measured in the proton-induced reactions p+^{232}Th \to ^{233}Pa, p+^{238}U \to ^{239}Np and p+^{242}Pu \to ^{243}Am (at proton energy E_p=13, 20, 40 and 55 MeV). The fragment mass and energy distributions (MEDs) have been analyzed in terms of the multimodal fission. The decomposition of the experimental MEDs onto the MEDs of the distinct modes has been fulfilled in the framework of a method that is free from any parameterization of the distinct fission mode mass distribution shapes. The main characteristics for symmetric and asymmetric modes have been studied in their dependence on the compound nucleus composition and proton energy. The manifestation of multimodal fission in average gamma-ray multiplicities $\langle E_{gamma}\rangle$ of fission fragments was also studied in this work.