Uncertainty budget assessment for the calibration of a silicon microdosimeter using the proton edge technique

The MicroPlus Bridge V2 silicon microdosimeter was exposed to collimated protons in a clinical radiotherapy beam, a mixed photon–neutron radiation field from a sealed 252Cf source and gamma-rays from a 137Cs source in order to investigate the accuracy and the uncertainty budget associated with the calibration of this detector by means of the proton-edge technique. At first, the energy values associated with the proton- and electron-edges were assessed for the detector under study by performing radiation transport simulations using the Monte Carlo code PHITS. After calibrating the detector in pulse amplitude using a pulse generator and in energy imparted using the PHITS-determined proton-edge, the accuracy of the calibration was tested by comparing the position of the electron-edge in the experimental microdosimetric spectra with the theoretical value obtained using PHITS. A study on the determination of which marker point (inflection point, maximum of the second derivative, intercept of the tangent through the inflection point) is the most accurate and least affected by the arbitrary choice of the fitting range is included in the article, proving that the detector can be successfully calibrated using the proton-edge technique with a combined uncertainty of 4%.