Neutron capture measurements of the noble gas isotopes Ne-22, Ar-40 and Kr-78,Kr-80,Kr-84,Kr-86 in the keV energy region

摘要

At the Karlsruhe and Tubingen 3.75 MV Van de Graaff accelerators the cross sections of Ne-22(n, gamma)Ne-23 (37.2 s), Ar-40(n, gamma)Ar-41 (1.83 h), and the Kr isotopes Kr-78(n, gamma)Kr-79(m) (50 s), Kr-78(n, gamma)Kr-79(35.04 h), Kr-80(n, gamma)Kr-81(m) (13.1 s), Kr-84(n, gamma)Kr-85(m) (4.48 h),and Kr-86(n, gamma)Kr-87 (76.3 m), were measured in the keV energy range by the regular and/or the fast cyclic activation techniques via the characteristic gamma-ray lines in the decay of the respective residual nuclei. High pressure gas samples which consisted of Ne-22-Kr and Ar-40-Kr mixtures were irradiated using the Li-7(p, n) and T(p, n) reactions. The measurements were carried out at the neutron energies 25, 30, 52, 104, 149, 180, and 215 keV. Stellar reaction rates for thermal energies kT between 1 and 250 keV were determined. The population probability of the Kr-85(m) isomeric state by neutron capture of Kr-84 was studied as a function of neutron energy. No significant energy dependence was found. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 37]