A MWPC with a cathode coupled delay line read-out as radioactivity detector for DNA repair studies

A non selective method for the isolation of DNA repair-deficient mutants in mammalian cells is discussed. The method requires radioactive labelling of the short DNA sequences synthesized during repair of damaged regions. Mutants should be recognized by the absence of radioactive incorporation into thier DNA. A multiwire proportional chamber (MWPC) is proposed as a suitable radioactivity detector. The performance of a MWPC prototype with a cathode coupled delay line read-out is described and is shown to be adequate for this application. The main avaantages of a MWPC are reviewed with respect to other methods used for β− radioactivity counting of biological samples, such as liquid scintillators or autoradiography: the proposed detection method is non destructive for the cells, which are being kept alive for further biological studies; furthermore many cell clones can be screened within a reasonable time.