Compton spectrometer for X-rays in the energy range from 10 to 150 keV

To measure directly energy spectra of X-ray beams produced by clinical equipment, it is necessary to reduce the intensity in order to avoid pulse pile-up and radiation damage to the detector. An alternative method is to measure the scattered beam in a definite angle and to use a formalism for Compton scattering, utilizing the Klein-Nishina cross-section and parameters related to the experimental setup, to reconstruct the primary X-ray beam spectrum. This method allows the use of the detector in short distances from the X-ray emitter using anode current similar to that utilized in clinical practice. In this work, we developed a Compton spectrometer consisting of a CdTe detector and associated electronics, collimators and a PMMA rod with 6 mm diameter as scatterer, without any shielding to avoid spurious fluorescence radiation. Primary beam spectra were obtained for an industrial equipment, with constant potential, in the range 20 to 150 kV, and for a mammography clinical apparatus, in the range 20 to 35 kV, from the spectra of scattered beams at an angle close to 90 deg. A stripping method has been applied to correct the raw spectra before the reconstruction of the primary spectra. The experimental energy resolution obtained for the 17.7 keV X-ray peak of an 241Am standard source was 0.448 keV (FWHM). In the Compton scattering measurements, the resolution was changed to 0.611 keV for the 17.5 keV Kα1 X-ray of Mo, mainly due to Doppler broadening in the scatterer. This resolution is similar to that obtained in direct measurements published in recent literature. (author)