Neutron activation of natural zinc samples at kT=25 keV

The neutron-capture cross sections of Zn-64, Zn-68, and Zn-70 have been measured with the activation technique in a quasistellar neutron spectrum corresponding to a thermal energy of kT = 25 keV. By a series of repeated irradiations with different experimental conditions, an uncertainty of 3% could be achieved for the Zn-64(n, gamma)Zn-65 cross section and for the partial cross section Zn-68(n, gamma)Zn-69(m) feeding the isomeric state in Zn-69. For the partial cross sections Zn-70(n, gamma)Zn-71(m) and Zn-70(n, gamma)Zn-71(g), which had not been measured so far, uncertainties of only 16% and 6% could be reached because of limited counting statistics and decay intensities. Compared to previous measurements on Zn-64,Zn-68, the uncertainties could be significantly improved, while the Zn-70 cross section was found to be two times smaller than existing model calculations. From these results Maxwellian average cross sections were determined between 5 and 100 keV. Additionally, the beta-decay half-life of Zn-71(m) could be determined with significantly improved accuracy. The consequences of these data have been studied by network calculations for convective core He burning and convective shell C burning in massive stars.