Proton Dosimetry: Measurement of Depth Doses from 185-MeV Protons by Means of Thermoluminescent LiF

As the radiation energy spectrum usually changes with depth in an irradiated medium, an ideal dosimeter should give a signal which is proportional to the absorbed dose in the medium, irrespective of the radiation energy spectrum. Most dosimeters, however, deviate from this ideal behavior. An analysis is made of the correction factors involved when a detector is used for depth-dose measurements. The detector signal has to be corrected for (1) variations with depth of the relative energy absorption in detector and medium; and (2) variations with depth of the sensitivity of the detector. The sensitivity is defined as the signal per unit absorbed dose in the detector. In particular, the performance of thermoluminescent LiF for depth-dose measurements with high-energy protons (185 MeV) in a water phantom has been studied. The sensitivity of LiF as a function of phantom depth was studied by comparing the signals from a LiF dosimeter and a nitrogen-filled ionization chamber obtained at different phantom depths. ...