Application of Unfolding Techniques to Obtain an X-ray Primary Spectrum

Quality control of X-ray tubes for medical radiodiagnostic services is very important for those devices. Therefore, it is convenient to develop new procedures to characterise the X-ray primary beam, obtaining an accurate assessment of the actual photon spectrum. The Compton scattering technique is very useful to determinate X-ray spectra (in the 10 – 150 kVp range), avoiding the pile-up effect in the detector, as usually a large room is not available to apply other techniques. The Compton scattering procedure has been simulated using the Monte Carlo method. Furthermore, experimental measurements have been performed in order to validate the simulation model. The objective of these measurements is to acquire the pulse height distribution (PHD) recorded by the germanium detector for different primary beam spectra. After obtaining the PHD by a simulation process (MCNP code) or by experimental measurements, the primary spectrum is reconstructed using unfolding techniques such as a pseudo matrix inverse response. In particular, a Truncated Singular Value Decomposition technique has been applied in this work. Spectra so reconstructed are compared with theoretical primary spectra. A good agreement is found indicating the accuracy of the model developed.