ENERGY-DEPENDENCE OF PMOS DOSIMETERS

The results are presented of experimental work and numerical simulatio ns of the energy response for pMOS dosimetric transistors in their cus tom packages. Specially produced radiation soft pMOS transistors were used in this experimental work. The irradiation of pMOS dosemeters was done using Co-60 and Cs-137 sources, a dosimetric X ray unit, and a r adiotherapeutic linear accelerator in the range of photon energies fro m 21 keV to 8 MeV. The results show that package geometry and material s can significantly affect and smooth the energy dependence of pMOS tr ansistors and that in custom transistor packages they are not tissue-e quivalent dosemeters. Their response in the photon energy range of 45 to 250 keV is significantly larger than it should be (maximum dose enh ancement factor can be as high as 8) and some energy compensation tech niques must be used in order to fulfill the requirements of correspond ing standards.