Passive measurement of radon and thoron using TLD or SSNTD on electrets.

An electret is an electrical analogue of a permanent magnet and it carries a permanent electric charge. Our previous work has shown that such electrets are suitable for collecting decay products of radon and thoron in passive chambers. In the present work, the decay products are directly collected on the surface of a TLD or SSNTD providing in situ registration of the radiation from the decay products of radon and thoron. A 101. chamber, the sides of which were covered with a layer of Whatman No. 1 (W-1) filter paper, showed the following responses: (i) SSNTD (CR-39) recorded 92 +/- 13 tracks per cm2 per pCi/l, hr for radon and 9 +/- 1.5 tracks per cm2 per pCi/l. hr for thoron; (ii) for similar levels TLD (CaF2(Dy)) chips recorded an equivalent of 1.35 +/- 0.16 mR for radon and 0.30 +/- jk0.09 mR for thoron. Taking advantage of the differential response of the two chambers (one covered with a layer of W-1 filter paper and the other with a 75 mm polyurethene foam), simultaneous measurement of radon and thoron could be achieved.