Development of a ${}^{127}$Xe calibration source for nEXO

Abstract

We study a possible calibration technique for the nEXO experiment using a ${}^{127}$Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in ${}^{136}$Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of ${}^{127}$Xe and its small $Q$-value compared to that of ${}^{136}$Xe $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC.

24 pages, 16 figures