New radiative neutron capture measurement of 207Pb and 209Bi

This new measurement of the (n, ) capture cross sections of 207Pb and 209Bi has been motivated by i) the aim to achieve a better understanding of the s-process stellar nucleosynthesis in its termination region and ii) the design of accelerator driven systems (ADS) based on a lead-bismuth eutectic spallation core. The measurement has been performed using the total energy detector technique, since the lower neutron sensitivity achievable with such a detection system represents a clear advantage versus the alternative total absorption method. However, the former technique has been a source of controversy between experimentalists and therefore, an important part of the present work has been dedicated rst to the review and further development of the so called Pulse Height Weighting Technique (PHWT). Performing dedicated measurements at the CERN n TOF installation we have experimentally validated this technique, determining that a systematic uncertainty better than 2% can be achieved. Once the measuring technique has been demonstrated to be well under control, the measurement of the radiative capture cross section of 207Pb and 209Bi was carried out. Experimental sources of systematic uncertainty have been thoroughly treated by means of Monte Carlo simulations. An R-matrix analysis of the resolved resonance region has been performed for both nuclides, deriving the total resonance radiative capture cross section and resonance parameters where possible. Previous measurements of these isotopes were aected by large systematic corrections mainly due to the neutron sensitivity of the detection system used. In the present work these isotopes have been measured by employing an optimized detection setup, which permitted the determination of their cross sections with a practically negligible neutron sensitivity deviation. A comparison between the results obtained here and current evaluated data les is also presented, revealing high deviations mainly on s-wave resonances. These are to be ascribed to the high systematic uncertainty of the previous measurements, in which these evaluations are based. Implications of the new results in the eld of stellar nucleosynthesis as well as in ADS engineering are studied and discussed.