DEVELOPMENT OF A THICK GAS ELECTRON MULTIPLIER-BASED MULTI-ELEMENT MICRODOSIMETRIC DETECTOR

Abstract

Tissue Equivalent Proportional Counters (TEPCs) are considered the standard instrument for microdosimetry, aiming at measuring the distribution of the energy deposited by ionizing radiation in a micrometric target, and have been employed for a number of radiation physics, radiation protection and radiation biology applications. This study describes development procedure and performance of a novel multi-element TEPC. Following an extensive Geant4 simulation study, an advanced prototype multi-element gaseous microdosimetric detector was developed using the Thick Gas Electron Multiplier (THGEM) technique. The multi-element design was employed to increase the neutron detection efficiency. The prototype THGEM multi-element detector consists of three alternating layers of tissue equivalent plastic hexagons and each layer houses a hexagonal array of seven cylindrical gas cavity elements with equal heights and diameters of 17 mm. The final detector structure incorporates 21 gaseous volumes. Owing to the absence of wire electrodes, the THGEM multi-element detector offers flexible and convenient fabrication in contrast to the traditional wire-based methods. The detector responses to neutron and gamma-ray were investigated using the McMaster Tandetron 7Li(p,n) neutron source. The dosimetric performance of the detector is presented in contrast to the response of a commercial tissue equivalent proportional counter. The collected spectra exhibit the expected features of the lineal energy distributions for given proton beam energies. Compared to the 2 inch TEPC response, the detector gave a consistent microdosimetric response with a maximum discrepancy of 15% in measured neutron absorbed dose. An improvement of a factor of 3.0 in neutron detection efficiency has been accomplished. The prototype detector offers a simple fabrication process and provides the fundamental basis for development of a high efficiency TEPC dedicated for monitoring weak neutron radiation fields.