 Before etching, photographs are taken of the biological sample with the affixed CR-39 detector, with care taken to ensure that prescribed location marks on the detector are noted.After the etching process, automated or manual 'scanning' of the CR-39 is used to physically locate the ionising radiation recorded, which can then be mapped to the position of the radionuclide within the biological sample.There is no other non-destructive method for accurately identifying the location of trace quantities of radionuclides in biological samples at such low emission levels.