Neutron inelastic scattering and reactions in natural Pb as a background in neutrinoless double-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>β</mml:mi></mml:mrow></mml:math>-decay experiments

Abstract

Inelastic neutron scattering and reactions on Pb isotopes can result in $\ensuremath{\gamma}$ rays near the signature end-point energy in a number of $\ensuremath{\beta}\ensuremath{\beta}$ isotopes. In particular, there are $\ensuremath{\gamma}$-ray transitions in $^{206,207,208}\mathrm{Pb}$ that might produce energy deposits at the $^{76}\mathrm{Ge}{Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ in Ge detectors used for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ searches. The levels that produce these $\ensuremath{\gamma}$ rays can be excited by ($n,{n}^{'}\ensuremath{\gamma}$) or ($n,\mathit{xn}\ensuremath{\gamma}$) 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 $\ensuremath{\beta}\ensuremath{\beta}$-decay experiments. The cross section on $^{\mathrm{nat}}\mathrm{Pb}$ to produce the 2041-keV $\ensuremath{\gamma}$ ray from $^{206}\mathrm{Pb}$ is measured to be 3.6 \ifmmode\pm\else\textpm\fi{} 0.7 (stat.) \ifmmode\pm\else\textpm\fi{} 0.3 (syst.) mb at $\ensuremath{\approx}9$.6 MeV. The cross section on $^{\mathrm{nat}}\mathrm{Pb}$ to produce the 3061,3062-keV $\ensuremath{\gamma}$ rays from $^{207}\mathrm{Pb}$ and $^{208}\mathrm{Pb}$ is measured to be 3.9 \ifmmode\pm\else\textpm\fi{} 0.8 (stat.) \ifmmode\pm\else\textpm\fi{} 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 ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ in other $\ensuremath{\beta}\ensuremath{\beta}$ isotopes.