Abstract
During reactor power monitoring, compensated ion-chambers (CICs) are assembled by two similar gas-filled detectors. The gamma compensation of CICs is essential for detecting precision of thermal neutrons, and requires a pairs of fully matched voltages. Descriptions of detecting precision include current formation model, in which applied voltages and radiation strength act in the process of collecting charged particles. However, the model of CICs are seldom applied in design work to evaluate the monitoring precision. Here we show that imbalance degree of collecting charged particles leads to mismatch of saturation currents depending on difference of recombination and diffusion in each sub-chambers. We analyzed a coaxial type compensated ion-chamber (DL-126), and found that applied voltages and radiation strength have significant impact for ion recombination and electron diffusion. For increasing precision of CICs, this result suggests a dynamic way to evaluate the output deviation using radiation strength. Furthermore, we found the compensation factor of two sub-chambers is only related to the applied voltages and remain unchanged in various radiation. Our results demonstrate how collecting regulars of charged particles are likely to function in setting applied voltages, calculating the charge loss as well as quantifying the saturation currents. We anticipate our analysis to be a starting point for revising detection precision of compensated ion-chambers. For example, evaluating the neutron fluence in the reactor shutdown and restart process, including monitoring task after accident. Furthermore, dynamic precision evaluation of these detectors is a major target of prognostics and health management for Nuclear Instrument.
