The response of a MOSFET, p-type semiconductor and LiF TLD to quasi-monoenergetic x-rays.

A metal oxide semiconductor field effect transistor (MOSFET), p-type semiconductor and a TLD can all be used for x-ray dosimetry, with each system having the common disadvantage of a response which is dependent upon the incident photon energy, particularly for energies < 1 MeV. A Pantak HF-320 quasi-monoenergetic x-ray unit was used to determine the response of two Thomson and Nielson TN-502RD MOSFETs, a Scanditronix EDP-10 semiconductor (build-up cap 10 mm: tissue equivalence), an EDD-5 semiconductor (build-up cap 4.5 mm: tissue equivalence) and an Lif:Mg:Ti TLD over the energy range 12-208 keV. The sensitivity of each detector was normalized to the value produced by exposure to 6 MV x-rays. The maximum relative sensitivities of the two MOSFET detectors were 4.19 +/- 0.25 and 4.44 +/- 0.26 respectively, occurring at an incident x-ray energy of 33 keV. The maximum relative sensitivity of the Scanditronix EDP-10 of 2.24 +/- 0.13 occurred at 65 keV, and for the EDD-5, it was 7.72 +/- 0.45 at 48 keV. The TLD produced a maximum relative sensitivity of 1.31 +/- 0.09 at 33 keV. Compared with available data based on heteroenergetic x-ray sources, these measurements have identified a more representative response for each detector to low-energy x-rays.