Solar neutrinos can interact with the source isotope in neutrinoless double beta decay experiments through charged current and neutral current interactions. The charged-current product nucleus will then beta decay with a Q-value larger than the doubl
e beta decay Q-value. As a result, this process can populate the region of interest and be a background to the double beta decay signal. In this paper we estimate the solar neutrino capture rates on three commonly used double beta decay isotopes, uc{76}{Ge}, uc{130}{Te}, and uc{136}{Xe}. We then use the decay scheme of each product nucleus to estimate the possible background rates in those materials. As half-life sensitivities in future experiments approach $10^{28}$ y, this background will have to be considered.
The {sc Majorana} collaboration is searching for neutrinoless double beta decay using $^{76}$Ge, which has been shown to have a number of advantages in terms of sensitivities and backgrounds. The observation of neutrinoless double-beta decay would sh
ow that lepton number is violated and that neutrinos are Majorana particles and would simultaneously provide information on neutrino mass. Attaining sensitivities for neutrino masses in the inverted hierarchy region, $15 - 50$ meV, will require large, tonne-scale detectors with extremely low backgrounds, at the level of $sim$1 count/t-y or lower in the region of the signal. The {sc Majorana} collaboration, with funding support from DOE Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the {sc Demonstrator}, an array consisting of 40 kg of p-type point-contact high-purity germanium (HPGe) detectors, of which $sim$30 kg will be enriched to 87% in $^{76}$Ge. The {sc Demonstrator} is being constructed in a clean room laboratory facility at the 4850 level (4300 m.w.e.) of the Sanford Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded shield approach with the inner portion consisting of ultra-clean Cu that is being electroformed and machined underground. The primary aim of the {sc Demonstrator} is to show the feasibility of a future tonne-scale measurement in terms of backgrounds and scalability.
We investigate several Pb$(n,ngamma$) and Ge$(n,ngamma$) reactions. We measure $gamma$-ray production from Pb$(n,ngamma$) reactions that can be a significant background for double-beta decay experiments which use lead as a massive inner shield. Parti
cularly worrisome for Ge-based double-beta decay experiments are the 2041-keV and 3062-keV $gamma$ rays produced via Pb$(n,ngamma$). The former is very close to the ^{76}Ge double-beta decay endpoint energy and the latter has a double escape peak energy near the endpoint. Excitation $gamma$-ray lines from Ge$(n,ngamma$) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-beta decay using enriched germanium detectors.
