Introduction

Three natural occuring isotopes of radon are known:

1. ²²²Rn (radon) in the decay chain of ²³⁸U (uranium)
2. ²²⁰Rn (thoron) in the decay chain of ²³²Th (thorium)
3. ²¹⁹Rn (actinon) in the decay chain of ²³⁵U (uranium).

In general, ²²⁰Rn and ²¹⁹Rn are not relevant for the human radioactive exposure due to their very short half-life (less than 1 minute in each case). Therefore the main focus concerning measuring devices is set on ²²²Rn.

The short-lived decay products of ²²²Rn are electrically charged and therefore attached to aerosol particles in the air. This causes a radioactive disequilibrium between radon and its decay products in the natural environment. Radon decay products always exist in smaller concentrations than radon itself. Hence, measuring devices for radon can be grouped in instruments for analyzing radon gas (exclusively ²²²Rn) and/or instruments for radon decay products.

Because most of the relevant guidelines and reference levels are related to the ²²²Rn activity concentration, distributes measuring devices of this kind.

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