Speaker
Description
The determination of operational dosimetric quantities such as ambient dose equivalent $H^{*}$(10) and directional dose equivalent $H^{\prime}$(0.07, 0$^{\circ}$) in photon radiation fields is of great importance in radiation protection monitoring. This assessment typically involves configurations of several detectors, each of them calibrated and intended for the measurement of one single quantity, which leads to complex and expensive setups with multi-channel readouts. In the present work, a phoswich detector is designed to simplify the simultaneous measurement of $H^{*}$(10) and $H^{\prime}$(0.07, 0$^{\circ}$). In a phoswich detector two or more scintillation materials are optically coupled to a common light sensor. The difference between the time constants, and therefore between the different pulse shapes, allows to measure the energy deposition in each material. The feasibility of using this additional information for the calculation of a second operational quantity with a single detector in a photon radiation field is the main subject of this project. Furthermore, the functionality of this solution under pulsed and low energetic radiation fields will also be investigated. The detector in this study consists of an organic scintillator cast in a cylindrical shape and embedding a Gadolinium-Aluminium-Gallium-Garnet (GAGG) crystal in the form of a rectangular prism. The compound pulses from this detector are read by a single photomultiplier tube and processed digitally. Preliminary measurements have been carried out with an 18 mm diameter $\times$ 20 mm height existing prototype. Pulse shape discrimination results in excellent separation of the light signals from each material. The analysis shows that materials with comparable light yields work best together. The organic scintillator is produced and cast in-house. This enables adjustments to its properties to suit particular needs such as tissue equivalence or appropriate light yield. Simulations using Geant4 toolkit are used to study different detector geometries before manufacturing and experimental tests. These indicate that the ratio of energy deposition in the different materials varies over two orders of magnitude from 10 keV to 100 keV incident photon energy. This provides a highly sensitive measure to calculate the two operational quantities, whose ratio is also very dynamic in this energy range. Measurement results of the dosimetric quantities with an actual detector will be presented during the conference. It will be discussed under which circumstances such a detector can meet the requirements of the national metrology institute of Germany, Physikalisch-Technische Bundesanstalt Braunschweig (PTB).
