Dosemeter for low level external radiation

The description and calibration of a TL-based dosemeter for the measurement of low level external photon radiation are presented. The lower limit of detection is 2.5 μGy for 60 Co radiation. The dosemeter may be used for photon energies above approx. 60 keV. The dosemeter has a maximum over-response of 2.35 at 105 keV, relative to 60 Co radiation. For photon energies below 200 keV, the dosemeter will provide information concerning the effective energy of the photon field, thus improving the precision in the energy range of maximum over-response. For measurements of external doses from fallout of 137 Cs and 134 Cs, a relative calibration factor between 1.05 and 1.22 should be applied, depending on the relative contribution from Cs radiation compared with natural background