On field Spectrometry for diagnostic X-ray beams: Comparison between innovative devices

The knowledge of X-ray beam spectrum should be of great interest for the optimization of diagnostic procedures, allowing to reduce the patient dose improving the image quality. In fact, only the spectrometric analysis permits a complete characterization of the photonic beam both under qualitative and quantitative aspects enabling attenuation studies and quality parameters evaluation. Usually, the spectrometry of the diagnostic X-rays beam is not feasible on-site because the anode brilliance is always too great for any spectrometric detector. To overcome this difficulty, we have built up and tested a portable spectrometric system based on the Compton scattering effect: the X-ray spectrum, scattered by a suitable graphite target inside the chamber at a specific angle, is collected and reconstructed by the inversion of scattering matrices. To optimize the performance of this instrument, we have tested many kind of detectors and the reconstruction algorithm takes into account the detector efficiency and performs a parametric description of the bremsstrahlung in the diagnostic energy range (15 keV -150 keV). The second instrument is a real-time detector system capable to measure some parameters from the X-ray beam and the high- voltage generator. A PC runs the reconstruction of the spectrum starting from experimental parameters. Experimental results obtained with these two devices will be shown and compared each other, but also with spectra acquired with a nitrogen cooled HPGe detector in a laboratory facility (the gold standard not suitable for on-site measurements). Aim of this work is to present, characterize and compare these two innovative devices that can be simply implemented in every X-ray imaging machine to test, optimize but also control the performances.