Retrospective Rn-220 Measurements by Compact Discs

Recently, a method for retrospective
²²⁰
Rn measurements by etching alpha-tracks in compact discs (CDs) or digital video discs (DVDs) has been proposed. In that method the tracks at the front surface (with respect to the reading laser beam) of the discs are analyzed. These measurements are influenced by
²²²
Rn absorbed in the disc material and the signal must be corrected for
²²²
Rn presence. In this work we study whether the influence of
²²²
Rn can be eliminated if the back (labeled) side of the CDs is analyzed. Because of the coating on the back side of the disc,
²²²
Rn absorption is prevented and its influence on
²²⁰
Rn signal is significantly reduced. Moreover, it has been found that in most discs the signal at the back side is an order of magnitude greater than that at the front side, which significantly improves the sensitivity of the method. Thus, this work proposes a new practical approach for retrospective
²²⁰
Rn measurements of improved sensitivity and reduced
²²²
Rn influence.