CALCULATED α-INDUCED THICK TARGET NEUTRON YIELDS AND SPECTRA, WITH COMPARISON TO MEASURED DATA
Los Alamos National Laboratory, Los Alamos, New Mexico, USA 87545
One component of the neutron source associated with the decay of actinide nuclides in many environments is due to the interaction of decay α particles in (α,n) reactions on low Z nuclides. Measurements of (α,n) thick target neutron yields and associated neutron spectra have been made for only a few combinations of α energy and target nuclide or mixtures of actinide and target nuclides. Calculations of thick target neutron yields and spectra with the SOURCES code require α-energy-dependent cross sections for (α,n) reactions, as well as branching fractions leading to the energetically possible levels of the product nuclides. A library of these data has been accumulated for target nuclides of Z ≤ 15 using that available from measurements and from recent GNASH code calculations. SOURCES, assuming neutrons to be emitted isotropically in the center-of-mass system, uses libraries of α stopping cross sections, (α,n) reaction cross sections, product nuclide level branching fractions, and actinide decay α spectra to calculate thick target (α,n) yields and neutron spectra for homogeneous combinations of nuclides. The code also calculates the thick target yield and angle integrated neutron spectrum produced by α-particle beams on targets of homogeneous mixtures of nuclides. Illustrative calculated results are given and comparisons are made with measured thick target yields and spectra.
KEYWORDS: (α,n) neutron sources, thick target neutron yields, neutron spectra