An algorithm for automatic counting of electrochemically etched tracks in compact disks used for retrospective measurements of Rn-222

This work describes an algorithm for automatic counting of alpha tracks in compact disks used as detectors in retrospective measurements of ²²²Rn. Compact disks have shown to be sensitive retrospective radon monitors due to the high absorption ability to ²²²Rn and the track etch properties of the polycarbonate material of which they are made. Automatic counting of electrochemically etched (ECE) tracks in compact disks is impeded by several difficulties: they are relatively large and have specific intrinsic structure, which prevents automatic counting with general purpose image analysis software. In addition, at the time of etching the compact disks had been already in use for over several years and might have lots of scratches on their surface. The algorithm presented in this work avoids the typical difficulties encountered in counting ECE tracks in retrospective measurements of ²²²Rn with CDs and DVDs and provides reliable estimation of track densities. It successfully separates overlapping tracks and reliably distinguishes scratches and artifacts. The algorithm is tested by comparison with visual counting of ECE tracks and a very good agreement is found. The algorithm is implemented in a computer code and has been used in the last two years in real ²²²Rn measurements with CDs and DVDs.