Development of an advanced two-dimensional microdosimetric detector based on THick Gas Electron Multipliers

The THick Gas Electron Multiplier (THGEM)-based tissue-equivalent proportional counter (TEPC) has been proven to be useful for microdosimetry due to its flexibility in varying the gaseous sensitive volume and achieving high multiplication gain. Aiming at measuring the spatial distribution of radiation dose for mixed neutron-gamma fields, an advanced two-dimensional (2D) THGEM-TEPC was designed and constructed at McMaster University which will enable us to overcome the operational limitation of the classical TEPCs, particularly for high-dose rate fields. Compared to the traditional TEPCs, anode wire electrodes were replaced by a THGEM layer, which not only enhances the gas multiplication gain but also offers a flexible and convenient fabrication for building 2D detectors.

The 2D THGEM TEPC consists of an array of 3 × 3 sensitive volumes, equivalent to nine individual TEPCs, each of which has a dimension of 5 mm diameter and length. Taking the overall cost, size and flexibility into account, to process nine detector signals simultaneously, a multi-input digital pulse processing system was developed by using modern microcontrollers, each of which is coupled with a 12-bit sampling ADC.

Using the McMaster Tandetron ⁷ Li(p,n) accelerator neutron source, both fundamental detector performance, as well as neutron dosimetric response of the 2D THGEM-TEPC, has been extensively investigated and compared to the data acquired by a standard spherical TEPC. It was shown that the microdosimetric response and the measured absorbed dose rate of the 2D THGEM detector developed in this study are comparable to the standard 1/2" TEPC which is commercially available.

This study proved that the 2D TEPC based on the THGEM technology can be effectively used in microdosimetry studies and is a promising detector for measuring the absorbed dose rate distribution over an area in mixed radiation fields. This unique small gas cavity detector opens new possibilities in applications for high-intensity mixed radiation fields as well as in nanodosimetry.