Joint Institute for Nuclear Research Relativistic ... - Index of - JINR

DETERMINATION OF FAST NEUTRON SPECTRUM BY A DEFORMATION OF
THE REFERENCE SPECTRUM EXPANDED ON LEGENDRE POLYNOMIALS
ACCORDING TO REACTION RATES IN THRESHOLD DETECTORS
1
S.Korneyev, 2 A.Khilmanovich, 2 B.Martsynkevich
1
Joint Institute for Power and Nuclear Research-Sosny, Minsk, Belarus;
2
B.I.Stepanov Institute of Physics, Minsk, Belarus
Software for neutron spectra unfolding use experimentally determined reaction rates in
threshold detectors and energy dependence reaction cross-section in a range from 0.025 eV to
20 MeV (see, for example, [1]) For high neutrons energies (up to 100 MeV and more) the
information on energy dependence of reaction cross-section is not sufficient.
In the present work the method of spectra unfolding for fast neutrons in a range 0.2 …
100 MeV, based on use of the modified method of effective threshold cross-sections and a
method of deformation of a reference spectrum expanded on Legendre polynomials.
In traditional approach a deformation applied to find of a required differential spectrum φ(E).
Authors propose to use deforming function in the form of expansion on Legendre
polynomials for a finding of integrated spectrum F(E). It is shown that as F(E) is
monotonously decreasing function aspiring to zero at approach to the maximum energy of a
spectrum. This function can be presented shorter number of required factors a m of a
polynomial. In the developed program the reactions cross-sections was taken from library [2],
for those reactions which do not have cross-sections above 20 MeV results from [3] are used
up to 150 MeV. The account of such "tails" allows calculating more precisely effective cross
section, especially for the reactions having high thresholds.
The developed program was applied to fast neutron spectra unfolding in Quinta
facility irradiated by deuterons in the energy range 1 - 8 GeV (JINR, LHE, Dubna)
1. W.N. McElroy, S. Berg, T. Crockett, R. G. Hawkins, "A Computer-Automated Iterative
Method for Neutron Flux Spectra Determination by Foil Activation, Vol. I: A Study of the
Iterative Method," AFWL-TR-67-41 (September 1967)
2. M.B. Chadwick, et al., ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library
for Nuclear Science and Technology, UCRL-JRNL-225066 (October 2006)
3. A.J. Koning and D. Rochman, Nuclear Research and Consultancy Group (NRG), TENDL-
2011 http://www.talys.eu/
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