Low Radioactive Material Screening and Background Control for the PandaX-4T Experiment

TL;DR

This paper details the development and application of ultra-low background material screening techniques and background suppression methods for the PandaX-4T dark matter detector, achieving very low background rates.

Contribution

It introduces comprehensive material screening and surface treatment procedures, combined with Monte Carlo simulations, to minimize background in the PandaX-4T experiment.

Findings

Estimated background rates are (9.9 ± 1.9) × 10^{-3} mDRU for electron recoil.

Estimated nuclear recoil background rate is (2.8 ± 0.6) × 10^{-4} mDRU.

Detector krypton level is below 8 ppt.

Abstract

PandaX-4T is a ton-scale dark matter direct detection experiment using a dual-phase TPC technique at the China Jinping Underground Laboratory. Various ultra-low background technologies have been developed and applied to material screening for PandaX-4T, including HPGe gamma spectroscopy, ICP-MS, NAA, radon emanation measurement system, krypton assay station, and alpha detection system. Low background materials were selected to assemble the detector. Surface treatment procedures were investigated to further suppress radioactive background. Combining measured results and Monte Carlo simulation, the total material background rates of PandaX-4T in the energy region of 1-25 keV$\rm{}_{ee}$ are estimated to be (9.9 $\pm$ 1.9) $\times \ 10^{-3}$ mDRU for electron recoil and (2.8 $\pm$ 0.6) $\times \ 10^{-4}$ mDRU for nuclear recoil. In addition, $^{nat}$Kr in the detector is estimated to be <8 ppt.