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 (0𝜈𝛽𝛽) 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 timedependent detector response. The 36.3 day half-life of 127 Xe and its small 𝑄-value compared to that of 136 Xe 0𝜈𝛽𝛽 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. K: Double beta decay detectors, Neutrino detectors, Time Projection Chambers (TPC) * Here we assume that the electric field is constant throughout the active region of the TPC. Non-uniformities in the field would create non-uniforimities in both the recombination fraction and the drift velocity 𝑣 𝑑 , which would introduce additional second-order position dependencies in the detected light and charge signals.