Geometric Electrode Effects on the Induced Photocurrent in Polycrystalline Diamond Based X- Ray Dosimeters

Abstract

The aim of the study is to develop tissue equivalent CVD diamond based dosimeters with a carbon based electrodes. We have initially studied the dependence of induced X-ray photocurrent amplitude and time response as a function of electrode area under broad beam X-ray irradiation. For this purpose, we have fabricated circular electrode sandwich tested structures based on thermal grade polycrystalline CVD diamond with different 3 diameters. The X-ray photocurrent increases with increasing dose rate sub linearly. Although the photocurrent increases with increasing electrode diameter, the increase in current is less than expected from the increase in active area. To further investigate, a small detector based upon 4 separate circular pad was tested for sensitivity with respect to detector area, applied bias voltage and incident x-ray doserate. Additionally the rise time of these detectors was evaluated with respect to the same criteria from these tests there was a non-linear relationship of under response between detector area and sensitivity under broad beam irradiation, the cause of which has been attributed to edge effects, supported by the results from collimated beam measurements. The results from the rise time tests appear to indicate that the time dependent components of the detector response are affected primarily by the applied bias upon the detector and the quality of the material, with additional doserate related effects scaling with bias. The higher quality material was found to have a far greater dependence on applied bias than the lower quality sample, which varied little.

Keywords: CVD Diamond, Dosimetric Characteristic, Electrical Contact, Radiation Detector, Thermal Grade polycrystalline diamond.