On the dynamic two-dimensional charge diffusion of the interpolating readout structure employed in the MicroCAT detector

Abstract

An essential part of the MicroCAT detector is its interpolating readout concept. A theoretical description of the charge diffusion process on the two-dimensional resistive readout structure and its influence on the position reconstruction is carried out. The corresponding inhomogeneous, time-dependent diffusion equation, with the geometric boundary conditions of the readout cells taken properly into account, is solved numerically. Signals realistically distributed in space and time are used as input to simulate the detector response. The time development of two-dimensional charge distributions is investigated. Charge losses to neighbouring cells and distortions due to the linear four-node-encoding algorithm used for reconstructing the impact position of a photon are considered. Since the thermal noise of the resistive layer leads to a limited position accuracy, the spatial resolution is calculated as a function of the integration time, the event position and the gas gain for different resistivities of the readout structure. The time dependence of the simulated signals allows an estimation of the expected rate capability of a given readout structure. In order to verify the theoretical predictions a measurement using an injection of charge pulses in known positions was performed.