# Molecular sieve vacuum swing adsorption purification and radon reduction system for gaseous dark matter and rare-event detectors

**Authors:** R. R. Marcelo Gregorio, N. J. C. Spooner, F. Dastgiri, A. C. Ezeribe, G. Lane, A. G. McLean, K. Miuchi, H. Ogawa  
**arXiv:** [2312.07720](https://arxiv.org/abs/2312.07720)  
**Date:** 2023-12-12  
**Summary page:** https://www.summarizepaper.com/en/paper/2312.07720v2/

## Key points

- SF6 is an ideal target gas for directional dark matter experiments due to its unique properties.
- Contaminant gases such as radon, water, oxygen, and nitrogen need to be effectively removed when using SF6 to prevent unwanted background events and loss of detector gas gain.
- A novel molecular sieve (MS) based gas recycling system has been developed for the simultaneous removal of radon and common pollutants from SF6.
- The system utilizes Vacuum Swing Adsorption (VSA) technique for continuous, long-term operation and minimizes the amount of gas required in experiments.
- Low-radioactive MS materials like type 5A have been introduced to reduce radon emanation significantly compared to commercial counterparts.
- MS types 3A and 4A successfully absorb common pollutants and help mitigate against gain deterioration while recycling the target gas.
- Radon activity within the TPC detector was reduced substantially with an upper limit of less than 7.2 mBq at a 95% confidence level (C.L.).
- A ThGEM-based TPC detector setup was used to demonstrate the effectiveness of the gas system in maintaining stable detector operation over extended periods.
- The study provides a comprehensive solution for purifying SF6 gas in dark matter experiments by removing contaminants and minimizing background events, enhancing detector performance, and ensuring reliable data collection for future research endeavors.

## Summary

In the field of directional dark matter experiments, SF6 has emerged as an ideal target gas due to its unique properties. A critical challenge in using SF6 and other proposed gases is effectively removing contaminant gases such as radon, water, oxygen, and nitrogen. These contaminants can lead to unwanted background events and loss of detector gas gain over time. To address this issue, a novel molecular sieve (MS) based gas recycling system has been developed for the simultaneous removal of both radon and common pollutants from SF6. This innovative apparatus not only minimizes the amount of gas required in experiments but also utilizes a Vacuum Swing Adsorption (VSA) technique for continuous, long-term operation. The capabilities of this gas system were tested with a 100 L low-pressure SF6 Time Projection Chamber (TPC) detector. For the first time, a newly developed low-radioactive MS type 5A was introduced which significantly reduced radon emanation compared to commercial counterparts. The incorporation of MS types 3A and 4A proved successful in absorbing common pollutants and mitigating against gain deterioration while recycling the target gas. The reduction in radon activity within the TPC detector was substantial with an upper limit of less than 7.2 mBq at a 95% confidence level (C.L.). Additionally, a ThGEM-based TPC detector setup was utilized for performance testing to demonstrate the effectiveness of the gas system in maintaining stable detector operation over extended periods. Overall, this study presents a comprehensive solution for purifying SF6 gas used in dark matter experiments by effectively removing contaminants and minimizing background events. The development of low-radioactive MS materials offers promising advancements in enhancing detector performance and ensuring reliable data collection for future research endeavors in this field.