Interpretation of Threshold Fission Chamber Signals

The total thermonuclear-neutron fluxes in the two energy groups 1.4-6.5 and 6.5-14.2 MeV are determined by mathematical analysis of the signal from a fission chamber with ^sup 238^U using two proposed values of the effective fission threshold cross sections σ^sub eff1^ and σ^sub eff2^ in these groups and the generally accepted effective threshold cross section σ^sub eff^ encompassing both of these energy groups. It is shown that for the real ITÉR spectrum and for model spectra of thermonuclear neutrons, where the signals from a fission chamber with ^sup 238^U remains constant and are distinguished from one another by the ratio of the fluxes in these groups, the two effective threshold cross sections σ^sub eff1^ and σ^sub eff2^ remain constant, while the generally accepted effective threshold cross section σ^sub eff^ varies from one model spectrum to another. Using two fission chambers, one with ^sup 238^U and the other with ^sup 237^Np, makes it possible to expand the energy range and to determine the total neutron fluxes in the three energy groups.[PUBLICATION ABSTRACT]