STELLAR NEUTRON-CAPTURE CROSS-SECTIONS OF THE ND ISOTOPES

The neutron capture cross sections of Nd-142, Nd-143, Nd-144, Nd-145, Nd-146, and Nd-148 have been measured in the energy range from 3 to 22 5 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons wer e produced via the Li-7(p,n)(7) Be reaction by bombarding metallic Li targets with a pulsed proton beam. Capture events were registered with the Karlsruhe 4 pi Barium Fluoride Detector. The cross sections were determined relative to the gold standard. The experiment was difficult due to the small cross sections of the even isotopes at or near the m agic neutron number N=82, and also since the isotopic enrichment of so me samples was comparably low. The necessary corrections for capture o f scattered neutrons and for isotopic impurities could be determined r eliably thanks to the high efficiency and the spectroscopic quality of the BaF2 detector, resulting in a consistent set of (n,gamma) cross s ections for the six stable neodymium isotopes involved in the s proces s with typical uncertainties of 1.5-2 %. From these data, Maxwellian a veraged cross sections were calculated between kT=10 and 100 keV. The astrophysical implications of these results were investigated in an s- process analysis, which deals with the role of the s-only isotope Nd-1 42 for the N-s <sigma > systematics near the magic neutron number N=82 , the decomposition of the Nd abundances into the respective r-, s-, a nd p-process components, and the interpretation of isotopic anomalies in meteoritic material.