Speaker
Description
The prediction of prompt neutron spectra of the photon-induced reactions on the 238U and 232Th targets are needed in the treatment of experimental data of the reactions induced by quasi monochromatic γ-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility.
Unfortunately any experimental information concerning both the fission fragments and the prompt emission quantities for the monochromatic photon induced fission of 238U and 232Th is completely missing. Consequently the only way to predict the prompt neutron spectra of γ + 238U and γ + 232Th at incident energies Eγ ranging from 4 to 22 MeV, remains the use of the most probable fragmentation approach (known as the Los Alamos (LA) model) with input parameters provided by systematics. The LA version of Madland and Kahler [1] which consider different residual temperature distributions of the light and heavy fragment and the recent systematic of its input parameters [2] are employed.
At Eγ up to about 12 MeV, the spectra of prompt neutrons emitted only from the fission fragments of the main nucleus undergoing fission (i.e. 238U and 232Th, respectively) are considered. At higher Eγ multiple fission chances occur, so that the contributions of both, the prompt neutrons emitted from the fission fragments (FF) of each fissioning nucleus formed at the respective Eγ and of the so-called pre-fission neutrons must be taken into account.
At Eγ up to 22 MeV, only the fissioning nuclei of the main chain are involved (i.e. 238-236U, 232-230Th), their average excitation energies (at which the prompt emission calculations are performed) being given by iterative equations according to Refs.[3 - 6] and references therein.
The individual spectra of prompt neutrons emitted from the fission fragments Ni(E) of each fission chance (indexed i) and of each evaporated pre-fission neutron φev i(E) are then calculated without to need of the fission probabilities.
The total prompt neutron spectrum at a given Eγ is obtained as N(E) = NFF(E) + Nprefiss(E) in which both components NFF(E) and Nprefiss(E) are calculated as a superposition of individual spectra Ni(E) and φev i(E) respectively, weighted with the fission probabilities of each chance PFi and the average numbers of prompt neutrons. The fission probabilities can be taken as photo-fission cross-section ratios resulting from nuclear reaction calculations, i.e. RFi = σγ,xnf / σγ,F (in which x = i-1).
The present prediction of prompt neutron spectra is based on RFi obtained from the photon induced reaction calculations performed with the EMPIRE code, according to Ref.[7]
[1] D.G.Madland and A.C.Kahler, Nucl.Phys.A 957 (2017) 289-311 and corrigeum Nucl.Phys.A 961 (2017) 216-217.
[2] A.Tudora, Eur.Phys.J. A, 56 (9), (2020) 225.
[3] A.Tudora, G.Vladuca, B.Morillon, Nucl.Phys.A 740 (2004) 33-58.
[4] R.Capote et al. Nucl.Data Sheets 131 (2016) 1-106.
[5] A.Tudora, F.-J.Hambsch, V.Tobosaru, Phys.Rev.C 94 (2016) 044601.
[6] A.Tudora, F.-J.Hambsch, V.Tobosaru, Nucl.Sci.Eng. 192 (2018) 52-69.
[7] M.Sin, R.Capote, M.W.Herman, A.Trkov, B.V.Carlson, Phys.Rev.C 103 (2021) 054605.