On the Determination of Microdosimetric Parameters in Time-Varying Radiation Fields: The Variance-Covariance Method

Microdosimetric measurements in their usual form are difficult in fields of high intensity where events, i.e., passages of charged particles, cannot be individually resolved. The variance method can then be utilized to obtain the dose averages of the microdosimetric distributions from repeated measurements over finite time intervals. An essential condition for the method is that the dose per measurement interval is constant, but this condition cannot be fulfilled in accelerator-produced fields that consist of variable radiation pulses. A modified method is therefore proposed that does not require equal doses per measurement interval. It utilizes two detectors that operate in phase, and it derives the microdosimetric parameters from the difference between the variance of the signal from one detector and the covariance of the concomitant signals from the two detectors.