Even-odd Effects in the Prompt Emission in Fission of Even-even Actinides☆

Abstract The even-odd effects in prompt emission received less attention compared to the extensively studied Z even-odd effects in fragment distributions. In this context, the present work is focusing on the even-odd effects (in both Z and N) appearing in the prompt emission of even-even nuclei fissioning spontaneously ( 252 Cf, 236,238,240,242,244 Pu) and by thermal neutron induced fission ( 233,235 U, 239 Pu). The study shows that these effects are mainly due to the Z even-odd effects in fragment distributions and ΔZ and the N even-odd effects in average neutron separation energies. The most pronounced even-odd effect in prompt emission is observed for the prompt neutron multiplicity, its global size decreasing with increasing fissility. The N even-odd effect in , influences the global even-odd effect in prompt neutron multiplicity often in an opposite way compared to the Z even-odd effect. The global N even-odd effect in is considerably higher in the case of 236-244 Pu(SF) compared to other neutron induced fissioning nuclei with comparable mass. (TKE) shows an increase of the Z even-odd effect with increasing TKE. Compared to 233,235 U(n th ,f), 239 Pu(n th ,f) and 252 Cf(SF) for which these effects show a decrease for heavier fissioning systems, in the case of 236-244 Pu(SF) this behaviour is not visible. The comparison of even-odd effects of 240 Pu(SF) and 239 Pu(n th ,f) showed i) a higher even-odd effect in Y(Z) and ΔZ for SF confirming the Z even-odd effect decrease with increasing excitation energy and ii) the higher N even-odd effect in for SF impacts the prompt emission leading to a lower Z even-odd effect in prompt neutron multiplicity of 240 Pu(SF) compared to 239 Pu(n th ,f).