Removing krypton from xenon by cryogenic distillation to the ppq level

TL;DR

This paper presents a cryogenic distillation method that effectively removes krypton from xenon to ppq levels, significantly reducing radioactive background for dark matter detection experiments.

Contribution

A novel cryogenic distillation column design achieving the lowest krypton contamination levels in xenon to date, suitable for next-generation dark matter detectors.

Findings

Achieved krypton reduction factor of 6.4×10^5

Reached krypton concentration below 26 ppq

Demonstrated system stability at >3 kg/h process speed

Abstract

The XENON1T experiment aims for the direct detection of dark matter in a cryostat filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by radioactive decays inside the detector has to be sufficiently low. One major contributor is the $\beta$-emitter $^{85}$Kr which is an intrinsic contamination of the xenon. For the XENON1T experiment a concentration of natural krypton in xenon $\rm{^{nat}}$Kr/Xe < 200 ppq (parts per quadrillion, 1 ppq = 10$^{-15}$ mol/mol) is required. In this work, the design of a novel cryogenic distillation column using the common McCabe-Thiele approach is described. The system demonstrated a krypton reduction factor of 6.4$\cdot$10$^5$ with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of $\rm{^{nat}}$Kr/Xe < 26 ppq is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN.