Neutron inelastic scattering and reactions in natural Pb as a background in neutrinoless double-beta-decay experiments

TL;DR

This study measures neutron-induced gamma-ray production in natural lead isotopes to evaluate background signals near the double-beta decay energy in detectors, providing essential data for background modeling.

Contribution

It provides the first direct measurements of neutron reaction cross sections on natural lead relevant to double-beta decay experiments.

Findings

Measured cross section for Pb-206 at 9.6 MeV: 3.6 +/- 0.7 (stat.) +/- 0.3 (syst.) mb.

Measured cross section for Pb-207 and Pb-208 at 9.6 MeV: 3.9 +/- 0.8 (stat.) +/- 0.4 (syst.) mb.

Reported upper limits for other relevant gamma-ray transitions.

Abstract

Inelastic neutron scattering and reactions on Pb isotopes can result in gamma rays near the signature endpoint energy in a number of double-beta decay isotopes. In particular, there are gamma-ray transitions in Pb-206,207,208 that might produce energy deposits at the 76-Ge Q value in Ge detectors used for double-beta decay searches. The levels that produce these gamma rays can be excited by (n,n'gamma) or (n,xngamma) reactions, but the cross sections are small and previously unmeasured. This work uses the pulsed neutron beam at the Los Alamos Neutron Science Center to directly measure reactions of interest to double-beta decay experiments. The cross section on natural Pb to produce the 2041-keV gamma ray from Pb-206 is measured to be 3.6 +/- 0.7 (stat.) +/- 0.3 (syst.) mb at ~9.6 MeV. The cross section on natural Pb to produce the 3062-keV gamma ray from Pb-207 and Pb-208 is measured to be 3.9 +/- 0.8 (stat.) +/- 0.4 (syst.) mb at the same energy. We report cross sections or place upper limits on the cross sections for exciting some other levels in Pb that have transition energies corresponding to Q value in other double-beta decay isotopes.