Speaker
Description
Pre-fission neutrons influence the observed prompt fission neutron spectra (PFNS), TKE, average number of prompt fission neutrons, (n,F) and (n,xn) reaction cross sections. Though pre-fission neutrons in 235U(n,F) were first observed around En~14 MeV [1] and then at En~7 MeV [2], only now measured data base [3-6] allows to demonstrate the complex influence of fissility of nuclides 236U and 240Pu on the PFNS shape. The model parameters are fixed at thermal neutron energy [7] and the renormalized for the TKE measured data.
The PFNS shapes at En ~6-7 MeV are strongly correlated with nuclide fissilities in 235U(n,xnf) and 239Pu(n,xnf) reactions and competition of (n,xnX) reactions. Calculated exclusive (n,nγ), (n,2n)1,2 and (n,nf)1 pre-fission neutrons spectra allow to demonstrate that the amplitude of (n,nf) spectra is the largest for 235U(n,F) at En ~6.5 MeV (Fig.1) while for 239Pu(n,F) at En ~6.0 MeV (Fig. 2). When (n,nf) reaction competes only with (n,nγ) reaction, the pre-FNS shapes are rather similar (En ~ 5.5 MeV), though the contribution of (n,nf)1 is much higher in case of 235U(n,F) reaction. When the (n,2n) reaction channel opens, the pre-FNS shapes reveal drastic influence of (n,2n)1 and (n,2n)2 neutron spectra. The fig. 1 demonstrates partials for 235U(n, F) reaction, the numerical data [8] are compatible with data [4,5]. The fig. 2 demonstrates partials for 239Pu(n, F) reaction, while the data [3-6] are compatible with predicted (n,xnf) contributions [9]. The lower curves and data points show the partitioning of the PFNS into the (n, f), (n,nf) and (n,nf)1 contributions.
1. Yu.A. Vasil’ev, Yu.S. Zamyatnin et al., Soviet Physics JETP, 11, 483 (1960).
2. A. Bertin, R. Bois, J. Frehaut 3d All Union Conf.on Neutron Phys.,Kiev,9-13 Jun 1975, Vol.4, p.303 (1975).
3. P. Marini, J. Taieb, B. Laurent, et al., Phys. Rev. C 101, 044614 (2020).
4. K.J. Kelly et al., Eur. Phys. Journ. Web of Conf., 2020, v. 239, 05010.
5. K.J. Kelly, M. Devlin, J.A. Gomez, et al., LA-UR-18-30526, 2018.
6. K. J. Kelly, M. Devlin J.M. O’Donnel et al, Phys. Rev. C 102, 034615(2020).
7. V.M. Maslov, N.A. Tetereva, V.G. Pronyaev et al., Atomic Energy, 108, 432 (2010)
8. V.M. Maslov, N.V. Kornilov, A.B. Kagalenko et al., Nucl. Phys. A 760, 274 (2005), https://www-nds.iaea.org/minskact/data/92235f18.txt.
9. V.M. Maslov, Atomic Energy, 103, No. 2, 633 (2007)
| The speaker is a student or young scientist | No |
|---|---|
| Section | 2. Experimental and theoretical studies of nuclear reactions |
