THE STELLAR (n, γ) CROSS SECTION OF THE UNSTABLE ISOTOPE ~(163)Ho AND THE ORIGIN OF ~(164)Er

摘要

The stellar (n, γ) cross section of the unstable isotope ~(163)Ho (t_(1/2) = 4570 yr) has been experimentally determined relative to that of gold by means of the activation method. In the course of this experiment, a number of decay parameters for ~(164)Ho have been remeasured and improved. A sample containing 6.62 x 10~(17) ~(163)Ho atoms was irradiated in a quasi-stellar neutron spectrum corresponding to a thermal energy of kT = 25 keV. This sample was produced from ~(162)Er, and the remaining impurity was sufficient to determine the ~(162)Er cross section simultaneously. For ~(163)Ho, a stellar cross section of < σv >/v_T = 2125 ± 95 mbarn at kT = 30 keV was found as the sum of the partial cross sections feeding the ground and isomeric states in ~(164)Ho. This value is of relevance for analyzing the abundance pattern in the s-process branchings at ~(163)Dy and ~(163)Ho that reflects the electron density during helium shell burning in low-mass stars.