Progress on using deuteron-deuteron fusion generated neutrons for 40Ar/39Ar sample irradiation

We present progress on the development and proof of concept of a deuteron-deuteron fusion based neutron generator for 40Ar/39Ar sample irradiation. Problems with back streaming electrons reported in an earlier abstract were solved by installation of an electrostatic shroud around the target. In a first set of experiments we determined neutron fluxes of 1.34 ± 0.04 ×107 cm-2s-1 by irradiation of indium foils and use of the activation reaction 115In(n,n')115mIn. In the central 4 × 4 mm of the sample chamber the neutron flux varies by 5 %. In ancillary experiments via irradiation of K salts and subsequent mass spectrometric analysis we determined the cross-sections of the 39K(n,p)39Ar reaction at 2.8 MeV to be 160 ± 35 mb (1σ). This result is in good agreement with bracketing cross-section data of 96 mb at 2.45 MeV and 270 mb at 4 MeV [Johnson et al., 1967; Dixon and Aitken, 1961 and Bass et al. 1964]. Our data disfavor a much lower value of 45 mb at 2.59 MeV [Lindström & Neuer, 1958]. Another ancillary experiment producing a result for the determination of the cross section for 39K(n,α)36Cl at 2.8 MeV, which is significant due to subsequent decay to 36Ar, will be available at the time of presentation of this abstract. While the neutron generator is designed for fluxes of 2×109 cm-²s-1, arcing in the sample chamber currently limits the power—straightforwardly correlated to the neutron flux—the generator can safely be run at. Further technical improvements are necessary to increase the neutron flux to make geologic sample irradiation possible in a reasonable experimental timeframe.