Ultra-Low background germanium spectrometers at the China Jinping Underground Laboratory

TL;DR

This paper describes the development and deployment of ultra-low background germanium spectrometers at China's Jinping Underground Laboratory, highlighting their design, background performance, and use in material screening for dark matter and neutrino research.

Contribution

It introduces new multi-detector germanium spectrometers with improved sensitivity and additional units installed at CJPL-II, enhancing material screening capabilities.

Findings

Achieved a minimum detectable activity of about 10 μBq/kg with the new spectrometer.

Installed fifteen GeTHU-like spectrometers at CJPL-II with about 1 mBq/kg MDA.

Detailed shielding design and background characteristics of the spectrometers.

Abstract

Four ultra-low background germanium spectrometers, called GeTHU, have been installed at the first phase of China Jinping Underground Laboratory (CJPL-I), and served for material screening of dark matter and neutrino experiments. Recently, a new multi-detector spectrometer with five germanium detectors has been developed and installed at the second phase of CJPL (CJPL-II) with a minimum detectable activity (MDA) of about 10 {\mu}Bq/kg. In addition, another fifteen GeTHU-like spectrometers have been installed at CJPL-II with an MDA of about 1 mBq/kg. This paper will introduce the ultra-low background germanium spectrometers including shielding design, background characteristics and application to material screening.