Average Quality Factor and Dose Equivalent Meter Based on Microdosimetry Techniques

Abstract

A compact device based on the TE proportional counter to measure dose equivalent, absorbed dose, and effective quality factor in mixed radiation fields is described. This device processes pulses as they are collected rather than waiting for an entire pulse height distribution. The conversion of linear energy y to linear energy L is made according to the relationship L = 8y/9. Pulses from the counter and preamplifier have rise times between 300 ns and 2 µs and voltages between 7 mV and 10 V. The range of four decades in the voltage signal requires two identical channels for detecting, storing and converting peak values. One channel operates on pulse heights between 7 mV and 156 mV while the other operates between 156 mV to 10 V. The peak detection unit uses a very high speed differentiator and two high speed comparators. The first comparator is a zero crossing detector and the second is a threshold detector connected to the amplifier stage. The combination of the two comparator output signals allows the triggering of the sample-and-hold circuit only at a peak value of the pulses. Digitisation of pulse height is performed by an 8-bit analog-to-digital converter and data processing is carried out by a MIW micro-computer based on a Z8 monochip. Measurements in monoenergetic neutron beams and mixed radiation fields are given to illustrate the proper operation of this device.