Removal of spallation-induced tritium from silicon through diffusion

TL;DR

This study explores a high-temperature baking method to effectively remove cosmogenic tritium from silicon, reducing radioactive backgrounds in sensitive detectors for rare event searches.

Contribution

It demonstrates that diffusion-based tritium removal in silicon is feasible at high temperatures, providing a practical approach to lower background radiation in low-background experiments.

Findings

Significant tritium removal achieved through baking above 400°C.

Complete de-trapping possible above 750°C.

Diffusion constants are comparable to thermally-induced tritium diffusion.

Abstract

Tritium, predominantly produced through spallation reactions caused by cosmic ray interactions, is a significant radioactive background for silicon-based rare event detection experiments, such as dark matter searches. We have investigated the feasibility of removing cosmogenic tritium from high-purity silicon intended for use in low-background experiments. We demonstrate that significant tritium removal is possible through diffusion by subjecting silicon to high-temperature (> 400C) baking. Using an analytical model for the de-trapping and diffusion of tritium in silicon, our measurements indicate that cosmogenic tritium diffusion constants are comparable to previous measurements of thermally-introduced tritium, with complete de-trapping and removal achievable above 750C. This approach has the potential to alleviate the stringent constraints of cosmic ray exposure prior to device fabrication and significantly reduce the cosmogenic tritium backgrounds of silicon-based detectors for next-generation rare event searches.