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

AbstractThe 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 (252Cf, 236,238,240,242,244Pu) and by thermal neutron induced fission (233,235U, 239Pu). 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 <Sn>, 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 <Sn> is considerably higher in the case of 236-244Pu(SF) compared to other neutron induced fissioning nuclei with comparable mass. <ν>(TKE) shows an increase of the Z even-odd effect with increasing TKE. Compared to 233,235U(nth,f), 239Pu(nth,f) and 252Cf(SF) for which these effects show a decrease for heavier fissioning systems, in the case of 236-244Pu(SF) this behaviour is not visible. The comparison of even-odd effects of 240Pu(SF) and 239Pu(nth,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 <Sn> for SF impacts the prompt emission leading to a lower Z even-odd effect in prompt neutron multiplicity of 240Pu(SF) compared to 239Pu(nth,f)