Radon monitoring in the Kamioka mine

Radioactivity from radon is one of the main backgrounds for low energy experiments, like Super-Kamiokande and the other experiments hosted in Kamioka Observatory. In addition, it is an issue for the safety of the researchers and technicians working in underground laboratories. In the Kamioka Observatory, a total of 29 1-L radon detectors are deployed in different areas in order to monitor the radon concentration and ensure it stays below a certain limit. Here we briefly describe the 1-L radon detector system and their Raspberry Pi-based data acquisition system. The evolution of the tunnel's radon concentration over the last 3 years is then shown and discussed.