Abstract
Recent developments in theoretical modeling and in computational power have allowed us to make significant progress on a goal not achieved yet in nuclear theory: a fully microscopic theory of nuclear fission. The complete microscopic description remains a computationally demanding task, but the information that can be provided by current calculations can be extremely useful to guide and constrain phenomenological approaches. First, a truly microscopic framework that can describe the real-time dynamics of the fissioning system can justify or rule out assumptions and approximations incompatible with an accurate quantum treatment or with our understanding of the inter nucleon interactions. Second, the microscopic approach can be used to obtain trends such as: the excitation energy sharing mechanism between fission fragments (FFs) with increasing excitation energy of the fissioning system, the angular momentum content of the FFs, or even to compute observables that cannot be otherwise calculated in phenomenological approaches or even measured, as in the case of astronomical environments. Merely the characterization of the trends would be of great importance for various application. We present here arguments that a truly microscopic approach to fission does not support the assumption of adiabaticity of the large amplitude collective motion in fission, particularly starting from the outer saddle down to the scission configuration.
Highlights
Reviewed by: Giuseppe Verde, National Institute for Nuclear Physics, Italy Armen Sedrakian, Frankfurt Institute for Advanced Studies, Germany
Of particular importance are applications to observables that cannot be directly measured in experimental setups, and their dependence of the excitation energy in the fissioning system
A few more crucial theoretical results have been firmly established: (i) the defining role of quantum shell effects [8, 9] and in particular the special role played by the pairing type of nucleon-nucleon interaction in shape evolution [10, 11]; (ii) the fact that the subsequent emission of neutrons and gammas can be described quite accurately using statistical methods [12, 13]; (iii) and that the non-relativistic Schrödinger equation should be adequate as well, as no genuine relativistic effects, such a retardation, are expected to play any noticeable role in fission dynamics
Summary
In a matter of days after Hahn and Strassmann [1] communicated their yet unpublished results to Lise Meitner, she and her nephew Otto Frisch [2] understood that an unexpected and qualitatively new type of nuclear reaction has been put in evidence and they dubbed it nuclear fission, in analogy to cell divisions in biology. Meitner and Frisch [2] gave the correct physical interpretation of the nuclear fission mechanism They understood that Bohr’s compound nucleus [6] is formed after the absorption of a neutron, which eventually slowly evolves in shape, while the volume remains constant, and that the competition between the surface energy of a nucleus and its Coulomb energy leads to the eventual scission. Theorists believed that the nuclear shape evolution until the moment of scission was so slow that individual nucleons had a sufficient time to adapt to avoided single-particle level crossings [14] and the entire nucleus would follow the lowest “molecular term,” using the FIGURE 1 | The schematic evolution of the single-particle nucleons levels (Upper panel) and of the total nuclear energy (Lower panel) as a function of deformation parameter q [10, 16, 17]. The collective DoF would always follow the lowest “molecular orbital” and only work would be performed on the intrinsic DoF, and with no heat transfer, and the intrinsic system would remain “cold” during the entire evolution
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