Measurement of 208 Pb(n ,γ ) 209 Pb Maxwellian averaged neutron capture cross section

The doubly magic $^{208}\mathrm{Pb}$ nucleus is a bottleneck at the termination of the $s$-process path due to its very low neutron capture cross section. This cross section is also important for the decomposition of $s$, $r$ processes and U/Th radiogenic decay contributions to the Pb-Bi solar abundances. The $^{208}\mathrm{Pb}(n,\ensuremath{\gamma})^{209}\mathrm{Pb}$ cross section was measured at the Soreq Applied Research Accelerator Facility Phase I using an intense quasi-Maxwellian neutron source produced by irradiation of the liquid-lithium target with a 1.5-mA continuous-wave proton beam at 1.94 MeV. The cross section was measured by counting the $\ensuremath{\beta}$ activity from the irradiated lead target. The measurement allowed us to evaluate the Maxwellian averaged cross section (MACS) at 30 keV obtaining a value of 0.33(2) mb. This has been compared with the earlier activation and time-of-flight measurements found in the literature. The MACS cross-sectional value of the $^{63}\mathrm{Cu}(n,\ensuremath{\gamma})^{64}\mathrm{Cu}$ reaction was determined in the same experiment and is compared to a recent published value.