The low- and high-temperature response of lithium fluoride dosemeters to X-rays

Abstract

The energy response of lithium fluoride (LiF) thermoluminescent dosemeters has been determined at two temperatures. Glow peaks 3,4, and 5 are measured at 240 degrees C and peaks 6 and 7 at 300 degrees C. In studying the response to X-radiation it was observed that the response of LiF chips to photons below 150 keV is greater, relative to cobalt-60, than that expected from the energy absorbed in the material. There is an enhancement of 10% at 240 degrees C and of about 100% at 300 degrees c for the same energy absorption. This effect is particularly important where precise measurement of X-ray dose is required and corrections of from 10 to 15% above the correction from rads in LiF to rads in water will be necessary depending upon the maximum read-out temperature. Qualitatively the enhancement may be explained in terms of the higher mean rate of linear energy transfer at low photon energies relative to cobalt-60 gamma rays.

LiF:Mg,Ti TLD response as a function of photon energy for moderately filtered x‐ray spectra in the range of 20–250 kVp relative to

“…The difference between the MC calculated and the measured response may not have been seen very often in the past because the effect is on the order of magnitude of investigators' uncertainties. 15,[25][26][27] Only by minimizing uncertainties in this study was the effect quantified.…”

“…25 In 1968, Tochilin et al 26 built on Cameron's earlier work and noted that neither set of TLD response data could be explained by the difference in mass energyabsorption coefficients of LiF and air. Budd et al 27 in 1979 reported an average 10% difference between measured and calculated TLD response as a function of photon energy relative to 60 Co at energies below 150 keV. This difference falls in the same range as the Davis et al 16 data, but with much larger uncertainties.…”

Photon energy dependence of sensitized LiF (TLD-700) phosphor

“…Budd et al 9 ), for example, have reported that for virgin LiF, a correction of 10 to 15% above the correction from the difference in mass energy absorption coefficients of LiF and water will be necessary for precise X-ray dose measurements, depending upon the maximum readout temperature. This is probably due to a minor contribution of peak 7 TL intensity during the low-temperature readout, as pointed out in Ref.…”

Determination of the intrinsic energy dependence of LiF:Mg,Ti thermoluminescent dosimeters for 125I and 103Pd brachytherapy sources relative to 60Co

“…The first is the TLD annealing and readout procedures among the investigators. In particular, the maximum temperature used during TLD readout has a strong effect on the observed TLD energy dependence, with higher readout temperatures causing a larger change in TLD response at low energies relative to 60 Co. 20,34,35 Future studies investigating the effect of heating rate on TLD energy dependence may also help contribute to a better understanding of these differences. The second is the underlying nature of the photon spectra for the brachytherapy sources versus the x-ray sources.…”