High Resolution Semiconductor Gamma Ray Detectors for Radionuclide Metrology

Quantitative, non-invasive X and gamma ray 3-D tomographic assessment of large, irregularly shaped, heterogeneous bodies is essential for efficient progress of environmental waste management. Currently, thousands of sealed containers with low-level radioactive waste are in storage. The material must be identified and quantified as a preliminary step to processing or storing the material. Current technology measures only the average distribution of radioactivity within a body. Emission Computer Temography (ECT) can in principal be used to provide a 3-D assessment of the distribution of radioactivity, but each detector technology currently available has shortcomings. Several wide bandgap compounds semiconductor materials offer the potential for addressing these shortcomings, but their performance is limited by poor transport of the holes. The project will address this need by fabricating a detector which uses a true Frisch grid, embedded inside the semiconductor device, to produce a signal due to electron transport alone. This structure offers the potential for much higher energy resolution with conventional electronics than any techniques currently used with compound semiconductor detectors.