Measurement of accelerator bremsstrahlung spectra with a high-efficiency Ge detector

A Compton spectrometer with a high-efficiency Ge detector was used to measure photon spectra from clinical accelerators. The response-function matrix for the detector system was determined using ten radioactive sources that emitted gamma rays of single energy ranging from 279-1525 keV. The system was tested by measuring the spectrum from a 60Co teletherapy machine. The energy distribution of tungsten target bremsstrahlung produced by 2.2, 2.5, 15, 20, and 25 MeV electrons in two clinical accelerators were determined. Theoretical thin-target calculations overestimate the number of photons in the high-energy regions of the spectra, as was expected. However, theoretical thick-target calculations underestimate the numbers of high-energy photons.