Spatially uniform calibration of a liquid xenon detector at low energies using K83mr

Abstract

A difficult task with many particle detectors focusing on interactions below approximately 100 keV is to perform a calibration in the appropriate energy range that adequately probes all regions of the detector. Because detector response can vary greatly in various locations within the device, a spatially uniform calibration is important. We present a new method for calibration of liquid xenon (LXe) detectors, using the short-lived (83m)Kr. This source has transitions at 9.4 and 32.1 keV, and as a noble gas like Xe, it disperses uniformly in all regions of the detector. Even for low source activities, the existence of the two transitions provides a method of identifying the decays that is free of background. We find that at decreasing energies, the LXe light yield increases, while the amount of electric field quenching is diminished. Additionally, we show that if any long-lived radioactive backgrounds are introduced by this method, they will present less than 67x10(-6) events kg(-1) day(-1) keV(-1) in the next generation of LXe dark matter direct detection searches.

Signal yields, energy resolution, and recombination fluctuations in liquid xenon

“…1 and 2, includes peaks from the 127 Xe L-shell electron capture at 5.2 keV to the 609 keV gamma emitted following 214 Bi β-decay. There is a large contribution at 41.6 keV from residual 83m Kr, an internal calibration source injected regularly during the acquisition [24,25]. Figure 3 shows part of the Compton plateau and the 661.7 keV photopeak from 137 Cs calibrations.…”

The XENON1T dark matter experiment

“…XENON1T uses 83m Kr (T 1/2 = 1.8 h), the short-lived daughter of 83 Rb, which delivers mono-energetic conversion electron lines at 32.1 keV and 9.4 keV [61,62]. The 83 Rb source is installed in the purification system to release the 83m Kr into the TPC when required.…”

Improved Limits on Scattering of Weakly Interacting Massive Particles from Reanalysis of 2013 LUX Data

“…A weak radial component moves drifting electrons inwards from the site of ionization by up to 4.6 cm for the outer bottom edge of the fiducial volume, in agreement with an electrostatic model of the drift field [12]. We account for this effect by exploiting the spatial uniformity of a 83m Kr calibration source [13,14] to derive a mapping between S2 and vertex position. Position variables used in later analysis refer to the reconstructed vertex: the standard deviations of the reconstructed x and y have a statistical contribution of 10 mm at the S2 threshold, and a 5 mm systematic contribution estimated from the reconstruction of the chamber walls and of a collimated neutron beam [15].…”