Radon Reference Chamber for Calibration of the Monitors

Abstract

Ningyo-toge Environmental Engineering Center of Japan Nuclear Cycle Development Institute has charge of the closed uranium mines, and the measurements of the atmospheric radon concentration on and around the closed mines have been performed as part of the environmental monitoring. In order to maintain the radon monitors the practical radon reference chamber was manufactured using the natural soil containing radium. The 7.5m³radon reference chamber is cylindrical, lying horizontal, and the radon concentration can be achieved to about 1000Bq/m³, and the temperature and humidity are controllable. Since the atmospheric pressure is about 10% low because the site location is 700mabove sea level, the chamber was structurally manufactured to resist pressure of even1 atm.
As a primary standard the weak radium solution is used, and gas charging type ionization chamber as a secondary standard is maintained to achieve the traceability of the radon monitors. The features of the chamber and the calibration technique are reported.