7 Li ( p , n ) 7 Be cross section from threshold to 1960 keV and precise measurement of the 197 Au ( n , γ ) spectrum-averaged cross section at 30 keV

Background: The 7 Li(p, n) 7 Be reaction is one of the most used nuclear reaction for accelerator-based neutron sources. There are few experimental cross section data in the double-value energy region and they are discrepant, as are the reaction yields. Purpose: We derive the 7 Li(p, n) 7 Be reaction cross section, and measure with small uncertainty the 197Au(n, γ ) 198Au spectrum-averaged cross section at neutron energy around 30 keV. Method: By irradiating Li metal targets over the proton energy range of 1879 to 1960 keV, thick target yields were measured using the generated 7 Be activity. Based on the theoretical description of the reaction yield, accelerator parameters and reaction cross sections are derived. Gold foils were activated with the neutron field generated by the (p, n) reaction on a Li target at a proton energy of about a half keV above the reaction threshold. Results: The thick target yield is well reproduced when the Breit-Wigner single-resonance formula for s-wave particles is used to describe the reaction cross section. The ratio between neutron and proton widths was found to be equal to n/p = 5.4 1 − Tth/Tp. The detailed balance principle is used to obtain the cosmologically important time-reversed 7 Be(n, p) 7 Li reaction cross section. The measured 197Au(n, γ ) 198Au spectrum-averaged cross section agrees with the value calculated from the ENDF/B-VIII.0 library. Conclusions: We demonstrated the feasibility of deriving the 7 Li(p, n) 7 Be reaction cross section from the thick target yield. Using the ratio between neutron and proton widths obtained in this work reduces the uncertainty in calculating the reaction cross section to a factor of 2.3.