Development of new radon monitoring systems in the Kamioka mine

TL;DR

This paper presents the development and deployment of a new high-sensitivity radon monitoring system using Raspberry Pi-based detectors, providing systematic radon measurements in the Kamioka Mine over a year to analyze seasonal and diurnal variations.

Contribution

The paper introduces a novel portable radon detector system with Raspberry Pi electronics and provides the first systematic radon concentration measurements in the Kamioka Mine.

Findings

Detected seasonal and day-night radon variations in the mine.

Achieved a detection limit of approximately 0.4 Bq/m^3 in one day.

Confirmed stability of the new Raspberry Pi-based electronics.

Abstract

Radioactivity from radon is a major threat for high-precision low energy physics experiments like the ones in the Kamioka Mine. We developed a new high sensitive radon monitoring system and conducted systematic radon concentration measurements for the first time in Kamioka. The system consists of portable radon detectors with a capacity of 1 L and new electronics based on Raspberry Pi. These radon detectors measure the radon in air with electro-static collection and a PIN photodiode. We measured the absolute humidity dependence of the 1-L radon detector for air to be $C_{F} (A_{H}) = (12.86 \pm 0.40) - (1.66 \pm 0.19) \sqrt{A_{H}}$ $\mathrm{(counts/day)/(Bq/m^3)}$. The background level of the 1-L radon detector is $0.65\pm0.15$ (stat.) count/day. This corresponds to a detection limit of $\sim0.4$ Bq/m$^3$ in a one-day measurement. Data was collected for a period of more than one year with twenty one 1-L radon detectors in the Kamioka mine. They indicate seasonal and day-night variations in radon concentration within the mine. These results also allow us to confirm the stability of the new Raspberry Pi electronics.