Neutron Capture of the Bottle-Neck Isotopes 138-Ba and 208-Pb, s-Process Studies and the r-Process Abundance Distribution.

Abstract

The capture cross-sections of 138-Ba and 208-Pb have been measured by time-of-flight (TOF) at the electron linear accelerator GELINA in the energy range 200 keV. The maxvellian averaged capture (MAC) cross section were determined vs temperature kT between 5 and 100 keV. The data were applied to carry out new parametric studies of the s-process. Two parametrized models were considered, pulsed s-process with one neutron source and double pulsed s-process, the combined burning of two neutron sources. Through the s-process abundance distributions the complementary semi-empirical p-process and r-process abundance distributions were determined. Especially the termination of the s-process was investigated. It was found that in the frame of the double pulse s-process model only negligible amounts of 209-Bi are synthetized. This would means that bismuth is mainly an r-process element.JRC.D-Institute for Reference Materials and Measurements (Geel