A Simple Radon Chamber for Educational Usage

J.A. Moore; A.L. Lehnert; S.-H. Hsu; and K.J. Kearfott (University of Michigan)

Radon chambers, designed with varying volumes and other characteristics, are used to calibrate radon detectors, to study the effectiveness of radon barriers, and to observe radon and radon progeny under different conditions. A very inexpensive 250 L radon chamber was designed to be part of a teaching laboratory to demonstrate radon build-up and decay phenomena, radon detector calibration, and radon and radon progeny disequilibrium. This was accomplished using an incubator with a radium dial source placed inside. This chamber design is unusual because of its small size and because the radium is inside the chamber, unlike many chamber designs for which the radium source is external and the radon gas is pumped into the chamber. Placing the radium source inside the chamber allows the radon concentration to be kept at a reasonably low level outside the chamber, and removes the need for a pump. The build-up in the chamber is characterized by collecting radon concentration data in the chamber for 3 d, every 4 h, after the source is placed inside. In order to obtain radon washout information, the source is then removed and the radon concentration is again measured every 4 h until the radon concentration in the chamber reaches background. This is repeated to obtain multiple sets of radon build-up and removal data. Plastic was used to line the chamber to make the data more reproducible as well as to lower the chamber's total radon removal rate to one corresponding to a 14 h half-life, which dominates the 3.8 d half-life of radon. The radon concentration is integrated at 1, 2, and 3-day intervals to obtain the total radon concentration-time product. Based upon 4 measurements, this data is reproducible to within 22% for 1 d, 15% for 2 d, and 8% for 3 d.

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