MEASUREMENTS OF BETA-RAY SPECTRA IN CANDU NUCLEAR GENERATING STATIONSUSING A SILICON DETECTOR COINCIDENCE TELESCOPE

The measurement of beta ray spectra at various work locations inside n uclear generating stations operated by Ontario Hydro is described. The measurements were carried out using an advanced coincidence telescope spectrometer using silicon detectors only. The spectrometer is capabl e of measuring electron energies over the range 60 keV-2500 keV with c lose to 100% coincidence efficiency. Photon rejection is carried out b y requiring a coincidence between either two or three silicon detector s. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermolu minescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm(-2)) results in a value of 2.7 3 +/- 0.77 and for the extremity dosemeter (240 mg.cm(-2)) an average value of 4.42 +/- 1.17 is obtained. These values are 57% and 120% grea ter, respectively, than the current values used by Ontario Hydro. In a ddition, beta correction factors for nine representative spectra were calculated for 40 mg.cm(-2) and 20 mg.cm(-2) chips and the results dem onstrate the benefits of decreased dosemeter thickness. The average va lue of the beta correction factor, as well as the spread in the beta c orrection factor, decreases dramatically from 4.80 +/- 2.1 (240 mg.cm( -2)) to 1.29 +/- 0.1 (20 mg.cm(-2)).