Bronisław Machaj1, Edward Świstowski1, Hoang C. Do1, Paweł Bilski2, Paweł Olko2
1Institute of Nuclear Chemistry and Technology, 16 Dorodna Str., 03-195 Warsaw, Poland,
2Health Physics Laboratory, Institute of Nuclear Physics, 152 Radzikowskiego Str., 31-342 Krakow, Poland
A gauge was developed for determining the dose rate distribution and surface activity of ophthalmic brachytherapy applicators, particulary for 106Ru applicators. A plastic f2´2 mm scintillator is used as the radiation detector, featuring a high pulse count rate, which results in a low 0.5% random error, due to good counting statistics. Automatic gain control of the photomultiplier tube (PMT) is achieved using a LED as the reference light source. The PMT operates in pulse mode. Long term gain variation due to fatigue of the PMT or ambient temperature variation is thus compensated for. The count rate error due to inaccurate setting of the high voltage supply of the PMT is 0.4%, and the instability error over 7 h of continuous operation does not exceed 1-2%, peak-to-peak.