Measurements of beta ray spectra in CANDU nuclear generating stations using a silicon detector coincidence telescope

The measurement of beta ray spectra at various work locations inside nuclear 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 capable of measuring electron energies over the range 60 keV- 2500 keV with close to 100% coincidence efficiency. Photon rejection is carried out by requiring a coincidence between either two or three silicon detectors. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermoluminescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm-2) results in a value of 2.73 ± 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% greater, respectively, than the current values used by Ontario Hydro. In addition, beta correction factors for nine representative spectra were calculated for 40 mg.cm-2 chips and 20 mg.cm-2 chips and the results demonstrate the benefits of decreased dosemeter thickness. The average value of the beta correction factor, as well as the spread in the beta correction factor, decreases dramatically from 4.8 ± 2.1 (240 mg.cm-2 to 1.29 ''1.2'' +-'' 0.1 (20 mg.cm-2). (author)