Tests of CDs/DVDs as passive radon and thoron detectors for mines and caves

Radon (
²²²
Rn) exposure is evident health hazard in a substantial number of underground mines. Exposure to thoron (
²²⁰
Rn) is usually considered to be of secondary importance, but radiation data regarding
²²⁰
Rn is very scarce compared to that for
²²²
Rn. In planning area and personal monitoring in underground places (mines and caves)
²²⁰
Rn issue should be addressed at least for two reasons: (1) to revise the possibility for increased exposure related to
²²⁰
Rn; (2) To ensure that
²²²
Rn results are not biased due to the sensitivity of detectors to
²²⁰
Rn, as it was recently found for many commercial
²²²
Rn detectors. In this report we test the applicability of CDs/DVDs as novel passive detectors for differential measurements of
²²²
Rn and
²²⁰
Rn in underground mines and caves. This is achieved by etching and counting alpha tracks at two different depths beneath the disk surface and analysis of the signals. To test the performance of the method and to check whether there is significant presence of thoron, 13 CDs were exposed in the underground galleries of a metal mine for 4 months. Results revealed that both
²²²
Rn and
²²⁰
Rn are present at the monitored places and in some cases the levels of
²²⁰
Rn are higher than those of
²²²
Rn. The CDs proved to be appropriate for measurements in the underground environment and stayed undamaged during the exposure. Additionally, dedicated laboratory experiments were made to test an approach to expand the range of
²²⁰
Rn concentrations measurable at high
²²²
Rn concentrations. The method proved its applicability for differential measurements of
²²²
Rn and
²²⁰
Rn over a wide range of concentrations. Radon concentrations well below the regulatory levels for workers are measurable even within 1 month exposure.