In-situ environmental radiation background measurement in the second phase of CJPL

TL;DR

This paper reports on the measurement of environmental radiation backgrounds in the second phase of China Jinping Underground Laboratory (CJPL-II), highlighting low radiation levels suitable for sensitive physics experiments and providing data for detector background modeling.

Contribution

It presents the first comprehensive measurement of cosmic-ray muons, radon, gamma rays, and neutrons in CJPL-II, supporting future rare-event physics research.

Findings

Effective reduction of environmental radiation due to rock overburden

Low levels of cosmic-ray muons, radon, gamma rays, and neutrons

Data supports detector background modeling for physics experiments

Abstract

China Jinping Underground Laboratory (CJPL), the deepest and largest underground laboratory worldwide, provides a low radiation background environment, which is necessary to frontier scientific research, such as the experimental studies of rare-event physics. Due to the almost filled space of CJPL-I and the requirement of future physics experiments, the construction of the second phase of CJPL (CJPL-II) was started in 2020 and all finished in 2024. In this work, we report the measured results of major environmental radiation in CJPL-II, including cosmic-ray muons, radon, gamma rays, and neutrons. Results indicate that the rock overburden and the radioactive background control effectively minimize the environmental radiation background. The scientific data presented also serve as an important basis to detector background modeling for the physics experiments in CJPL-II.