Determination of the Excitation Function of the (n,xt) Process on Beryllium via Activation in Diverse Neutron Fields and Unfolding Code Calculations

Beryllium samples together with sets of 12 flux monitor foils having different reaction thresholds were irradiated in six different d(Be) neutron fields (E_d = 17.5 to 30.0 MeV). The shapes of the neutron spectra were determined by using the SAND-II iterative unfolding code. In a second calculational step, the excitation function for the (n,xt) process on ⁹ Be was obtained from the neutron flux distributions and the measured tritium activities in beryllium samples. For this purpose, the SAND-II code as well as a generalized least-squares unfolding code were applied, and both gave similar results. The excitation function thus obtained is in excellent agreement with the values obtained by using monoenergetic neutrons in the region of 13 to 20 MeV.