HDR MICROSELECTRON QUALITY-ASSURANCE STUDIES USING A WELL-TYPE ION-CHAMBER

A modified Standard Imaging HDR 1000 re-entrant ion chamber has been used with an NE 2570/1 electrometer as part of a quality-assurance programme for checking Ir-192 source strengths and for source localization studies. The chamber measurements correlate well with in-air calibration measurements made over a three-month source-decay period; the maximum discrepancy between the in-air measurement and the re-entrant chamber measurement was 0.9%. The source position may be determined with an uncertainty of lower than 0.5 mm. The reproducibility of measurements made with each of four electrometers used with the reentrant ion chamber was typically 0.1% (1 sigma).