A new technique for calibrating a NaI(Tl) scintillometer used to measure gamma dose-rates in archaeological sites

A new calibration technique is described for relating the counting rate recorded by a portable 2' x 2' NaI(Tl) scintillometer to the dose-rate absorbed by quartz grains. The quartz grains were used as a thermoluminescence dosimeter employing the 1100C peak. To avoid fading the thermoluminescence was built up while the quartz grains were maintained at liquid nitrogen temperature. Four different spectral media were used for the calibration, namely potassium doped sand, uranium doped sand, thorium doped sand and uranium doped peat. In each case the dose-rates were also determined with LiF and CaSO4: Dy phosphors. The responses of the different phosphors are compared and the dependence of their sensitivity on gamma-ray energy is discussed. The emphasis is on the significance of the calibration procedure for a scintillometer employed on archaeological sites for dose-rate determination in connection with thermoluminescence dating. (orig.)