Practical radon detection by solid state nuclear track detectors

If the radioactive uranium family had not included a gas (radon), natural radioactivity would pose no health problem. Its rarer isotope, thoron gas, is neglected by legislation, but its daughter products can sometimes become dangerous, often because of the use of certain building materials. Solid state track detectors (SSNT) record individual alpha particle impacts without influencing their surroundings. These SSNTs are plastics chosen for their sensitivity to alpha particles. A simple alkaline treatment makes it possible to amplify, display and therefore count the tracks obtained. Placed in small passive cases, they become cheap dosimeters for use in the integrated measurement of radon and evaluation of the health risk. A practical examination shows that things are not quite so simple. The choice of an open dosimeter (free air SSNT) or closed (encased SSNT) is discussed. The practical differences are explained by studying the progressive change from an open dosimeter to closed dosimeter. Irrespective of the ease of use, open measurement is better for an overall assessment of the natural risk, while closed measurement is better for earth science measurements. The debate, for its part, is open. (author)