Two-parameter analysis of the temporal behaviour of resistive detectors

Abstract

The biggest constraint in the RPCs operation is the drop of their efficiency with the counting rate, consequence of charge gain decrease. This effect is normally attributed to the voltage drop on the dielectrics, although not supported by quantitative measurement. In this work we present the first results of a two-parameter analysis of the charge pulse height time variation from a cylindrical resistive detector, operating in proportional regime, under high irradiation rates. The dynamic behaviour of this detector was investigated through the determination of the time decay constants related to its stationary condition, where the charge gain becomes constant. To perform this study, a data acquisition system, which allows the users to observe in real-time the temporal variation of the energy spectrum, was specially designed. The fitting of the peak centroid position as a function of time, obtained for rates range from 220Hz up to 1230Hz, showed it can be described by a sum of two exponentials plus a constant term, what is in accordance to the dielectric delayed polarization processes.

Time Decay Constants of Resistive Detectors

“…Several groups have investigated the drop in the efficiency of Resistive Plate Chambers (RPCs) with increasing high voltage and counting rate [1,2,3,4,5]. In our previous papers [6,7,8,9] we have shown that this behavior is attributed to the voltage fall-off on the resistive electrodes, which reduces the effective electric field across the gas gap and consequently the charge gain. Our measurements were performed assuming a stationary regime and treating the dielectric as equivalent to a simple RC circuit with a time constant given by ρεε 0 , where ρ, ε, and ε 0 are the bulk resistivity, the static dielectric constant, and the permittivity of vacuum, respectively.…”