Development of a pulse processing system for real-time analysis of microdosimetric spectra

A new pulse processing system was developed for real-time analysis of microdosimetric spectra. Microdosimetric spectra from a tissue-equivalent proportional counter are usually extracted through complicated analysis steps after measuring event spectra with conventional pulse-height analyzers. The new pulse processing system consisted of a logarithmic and a linear peak-sensing ADCs and accumulates a dose spectrum directly without any post analysis. The logarithmic ADC was made by modifying a Wilkinson ADC and showed a satisfactory operation in the logarithmic scale. The new system was tested at the mixed neutron-gamma field of the McMaster Accelerator Laboratory. A conventional system was operated in parallel to estimate the reliability of the new system. The incident proton energy was varied from 1.8 to 2.3 MeV, which produced different neutron-gamma ratios through 7Li(p,n) and 7Li(p,p′γ) reactions. The counting rate during measurements changed from 560 to 1400 cps as the incident proton energy was increased by fixing the current at 45 μA. Microdosimetric spectra from the new system were consistent with those from the conventional system for various fields except for a little deviation induced by the nonlinearity of the logarithmic ADC. Both neutron and gamma-ray doses from two systems showed good agreement within 2%. Estimations regarding the dead time and tolerable counting rate will be continued.