Often only a single physical process or component is investigated in the simulation of radiation detector systems. The results are then considered to be representative of what is expected in the correlating physical experiment. Although singular assessments may serve as a good estimate, the overall performance of a radiation detector system depends on several physical processes and the performance of all components within the system. Our Geant4-based multiphysics simulation toolkit couples radiation transport with optical photon processes, providing simulations of radiation detector systems components from the scintillator through the photocathode of the photodetector. Work to incorporate the backend detector components, including the complete photodetector and subsequent electronics (e.g., amplifiers, digitizers), is underway. Geant4 is used to model the radiation transport and optical photon processes that occur in the front-end detector system components when exposed to a chosen source. These components include the scintillator, detector housing, optical coupling to the photodetector, and photocathode of the photodetector. Characteristics of several detector systems that have been studied include time response; pulse height spectra; number of photoelectrons per MeV; detector efficiency versus incident quanta energy; and effects on detector response due to change in geometries, materials, and reflectivity. Comparison of these characteristics by means of this toolkit enables the selection of the optimal individual components; thus, it is possible to specify the radiation detector system best suited to meet the requirements of any physical experiment.
Silicon-based photodetectors offer several benefits relative to photomultiplier tube-based scintillator systems. Solid-state
photomultipliers (SSPM) can realize the gain of a photomultiplier tube (PMT) with the quantum efficiency of silicon.
The advantages of the solid-state approach must be balanced with adverse trade-offs, for example from increased dark
current, to optimize radiation detection sensitivity. We are designing a custom SSPM that will be optimized for green
emission of thallium-doped cesium iodide (CsI(Tl)). A typical field gamma radiation detector incorporates thallium
doped sodium iodide (NaI(Tl)) and a radiation converter with a PMT. A PMT's sensitivity peaks in the blue wavelengths
and is well matched to NaI(Tl). This paper presents results of photomultiplier sensitivity relative to conventional SSPMs
and discusses model design improvements. Prototype fabrications are in progress.
Conference Committee Involvement (1)
Penetrating Radiation Systems and Applications VII
2 August 2005 | San Diego, California, United States