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

TL;DR

This paper proposes using a $^{127}$Xe electron capture source for in-situ calibration of the nEXO detector, enabling precise spatial response mapping without adding background noise.

Contribution

It introduces a method to produce and utilize a $^{127}$Xe calibration source for the nEXO experiment, with simulation-based projections of its calibration effectiveness.

Findings

Potential for continuous in-situ calibration during operation

Simulation results show high precision in spatial response correction

Source production process and preliminary tests demonstrated

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 ($0\nu\beta\beta$) 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 $0\nu\beta\beta$ 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.