Development of a ¹²⁷Xe calibration source for nEXO

We study a possible calibration technique for the nEXO experiment using a ¹²⁷Xe 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 ¹³⁶Xe. 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 ¹²⁷Xe and its small Q-value compared to that of ¹³⁶Xe 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.

Journal of Instrumentation, 17, P07028 (2022)