Low Background Stainless Steel for the Pressure Vessel in the PandaX-II Dark Matter Experiment

TL;DR

This paper presents the development and analysis of low-background stainless steel materials for the PandaX-II dark matter experiment's pressure vessel, focusing on reducing radioactive contamination to improve experimental sensitivity.

Contribution

It introduces custom low-background stainless steel and welding rods, and evaluates their suitability for use in sensitive underground physics experiments.

Findings

Anthropogenic 60 Co levels are at or below 1 mBq/kg.

TISCO stainless steel has comparable low radioactivity.

The materials are suitable for constructing low-background pressure vessels.

Abstract

We report on the custom produced low radiation background stainless steel and the welding rod for the PandaX experiment, one of the deep underground experiments to search for dark matter and neutrinoless double beta decay using xenon. The anthropogenic 60 Co concentration in these samples is at the range of 1 mBq/kg or lower. We also discuss the radioactivity of nuclear-grade stainless steel from TISCO which has a similar background rate. The PandaX-II pressure vessel was thus fabricated using the stainless steel from CISRI and TISCO. Based on the analysis of the radioactivity data, we also made discussions on potential candidate for low background metal materials for future pressure vessel development.