Growth of Semiconductors for Room Temperature Gamma-Ray Detection

There is a critical need for low cost, high performance gamma-ray detectors for identification and localization of special nuclear materials (SNM) such as plutonium and weapons grade uranium. Gamma ray spectrometers are an important tool in checking the proliferation of nuclear weapons. Cadmium zinc telluride (Cd1-xZnxTe or & quot;CZT & quot;) has emerged as the leading room temperature semiconductor gamma ray detector. However, despite decades of research and recent improvements in crystal growth and processing techniques, the yield of device grade CZT is low. To meet the needs of homeland security a lower cost alternative to CZT is desirable. Cadmium manganese telluride (Cd1-xMnxTe or & quot;CMT & quot;) shares many of the desirable nuclear detector properties of CZT including wide band gap, high atomic number and density and modestly high electron mobility-lifetime product. In addition, CMT has the potential to be a lower cost alternative to CZT. RMD has produced detector-grade CdTe crystals by the travelling heater method for many years and will adapt its technology to CMT. Twin-free CMT material with good uniformity and high resistivity ( & gt; 1010 cm) was obtained by the end of Phase I. In addition, gamma-ray detectors fabricated from this material exhibited stable, low noise and linear behavior. Phase II Plans The research in the Phase II project will be focused on the following main areas: (i) rigorous purification and growing single crystal ingots by THM, (ii) employing post growth annealing to reduce Te precipitates, (iii) characterizing chemical and physical properties, (iv) fabricating and characterizing detectors and (iv) applying depth correction techniques to CMT small pixel arrays. Commercial Applications and Other Benefits: In addition to nuclear non-proliferation, nuclear medicine, computed tomography and nondestructive testing are other applications where high performance, less expensive spectrometers will have beneficial applications. One medical application that RMD already takes part in is the production of surgical probes used for localizing radiopharmaceutical uptake. These tools have become part of a technique (sentinel node biopsy) that minimizes the debilitating nature of removing lymph nodes in monitoring the spread of breast cancer. As this technique has become more accepted for breast cancer, other treatment areas have been considered such as monitoring PET isotopes (emitting at 511 keV) which have greater specificity to cancer sites. A high energy emission presents a challenging probe design because of scattering and lack of efficiency. New large CMT detectors capable of scatter rejection would be a very welcome solution if available