Energy spectrum of the neutron source: 1 – integral yield of neutrons; 2 – yield of neutrons from spontaneous fission and the (α, n) reaction on 17,18O [(Th,Pu)O2]; 3 – yield of neutrons from to the (α, n) reaction on 17,18O; 4 – yield of neutrons from the (α, n) reaction on13С (RuS).