MEASUREMENT OF N-14(N,P)C-14 CROSS-SECTION FOR KT=25.3 KEV MAXWELLIANNEUTRONS USING GRIDDED IONIZATION-CHAMBER

We measured the N-14(n,p)C-14 reaction cross section for neutrons with a quasi-Maxwellian distribution of kT = 25.3 keV which is one of the key parameters for the s-process nucleosynthesis in astrophysics. Prot ons were detected with high efficiency using a gridded ionization cham ber. We employed a thick Li target and a 1.912 MeV proton beam for neu tron production, and a vacuum-evaporated melamine (C3H6N6) film as a N -14 sample. The absolute cross section was determined relatively to th e Li-6(n,t)alpha cross section by measuring the triton yield from a (L iF)-Li-6 film in place of melamine. Our result (1.70 +/- 0.08 mb) is a pproximately a factor 2 larger than the value reported in an earlier d irect measurement for the same Maxwellian neutron spectrum; it is cons istent with results deduced from monoenergetic neutrons or inverse rea ction.