New points of view on the nuclear properties of the fissile actinides

Abstract

Some arguments are presented in favor of an interpretation of the asymmetric fission, in which the light fission fragments are considered as being formed from the valence shells of the fissile nuclei. E.g., the peak-to-peak distance of the mass yield curve for neutron-induced fission is found to vary linearly with the number N p + N n of valence nucleons of the system undergoing fission. A detailed description of the asymmetric fission can be given, e.g. of 240Pu, which is based on binding energy calculations (energy release = 216.868 MeV) and energy relations holding in the valence shells. The neutron-proton interaction energy within the valence shells is proportional to the number N p × N n of n-p couples. Two methods are proposed for the calculation of E np . For 240 Pu, E np is about 63 MeV, i.e. the interaction energy per n-p couple is 263.1 keV. Other interaction laws between valence nucleons are described: the n-2n and 2n-2n repulsion laws, and the p-2p and 2p-2p repulsion laws. In even-even nuclei, the energy binding all the valence proton pairs is p· \\ ̄ gs 2p , where p is the number of proton pairs and σ 2p a mean “from core” separation energy per proton pair. Its value is independent of the number of pairs of nucleons of the other kind. For 240Pu, the energy binding any one of the six proton pairs to the core is only 5050 keV, and the energy binding any one of the ten neutron pairs to the core is as great as 8358 keV. This means that the protons are farther from the core than the neutrons. As the energy binding the protons to the core decreases rapidly with Z, and could be zero for Z = 108, neutrons have to be seen as bridges binding to the core the protons of the valence shell in the heavy actinides. This situation, and the weakness of all the valence shell interaction energies, explain that a neutron can induce shell alterations permitting the onset of stronger nuclear forces and nuclear fission.