Analysis of the prompt-neutron spectrum from spontaneous fission of 252Cf

The neutron energy spectrum from spontaneous fission of 252Cf is analysed in the framework of a complex cascade evaporation model up to 30 MeV in comparison with recent experimental results. The calculation is based on a semi-empirical description of the nuclear level density including the excitation energy dependence of shell effects and on realistic initial distributions of excitation energy which were determined accepting experimental data on the emission of neutrons and gamma rays as a function of both the total kinetic energy of the fragments and their mass number. The initial parameters and intermediate results are influenced strongly by shell effects. The integral spectrum obtained by weighted concentration of the calculated emission spectra for the fragments with mass numbers between 87 and 165 in steps of 3 agrees rather well with the corresponding evaluated energy distribution. Discrepancies between evaporation theory and experiment regarding the mean emission energy in the centre-of-mass frame as a function of fragment mass number as well as the high-energy end of the total spectrum are discussed considering other possible emission mechanisms which may be prevalent in the case of particular scission configurations.

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