The need to develop and harness advanced technology to detect nuclear materials is now in vivid focus. Many national-security users of radiation detectors must obtain and deliver fast and accurate information to intercept radioactive/nuclear materials and respond to a variety of threats. Ideally, the detectors would be compact, light weight, low maintenance, low power, able to identify radioactive isotopes, possess high signal-to-noise ratios, and capable of stand-off operation. Practically all of the proposed approaches have been limited by the quality of the materials used to produce the detectors, and resolution of the material problems has not been amenable to a quick and easy fix. For gamma detectors, the most promising approaches have involved the development of room-temperature semiconductor detectors based on cadmium zinc telluride (CZT) and scintillators based on the lanthanum halides. Because of deficiencies in the quality of the material, high energy-resolution CZT gamma spectrometers are still limited to relatively small dimensions, which makes them inefficient at detecting high photon energies and somewhat ineffective for weak radiation signals except in proximity. Scintillators based on lanthanum halides have also been limited to relatively small sizes. Both detectors are very attractive for a broad range of gamma-ray detector applications; however, increases in their efficiencies are needed without sacrificing the ability to operate at room temperature and to spectrally resolve isotopes of interest. To fully exploit these emerging technologies, it will be necessary to develop a detailed understanding of the underlying problems limiting the performance of devices and to apply this knowledge to improve the material quality. Progress is required in the following areas: growth of large uniform single crystals, reductions in carrier trapping, and improved device fabrication procedures. Despite the current material constraints, several types of new room-temperature gamma-ray detectors have been developed, some of which are now addressing important applications. This talk will summarize the material factors limiting the performance of solid-state detectors and scintillators and discuss ways to overcome them through appropriate corrections. Comments on the material limitations for advanced neutron detectors will also be discussed.

Cadmium zinc telluride (CZT) is the most promising semiconductor material today for production of X-ray and gamma detectors and imaging arrays operable at room temperature. The performance of CZT devices, the global capacity for growth of detector-grade crystals, and the size of the commercial market have progressed steadily over the past few years. Concurrently, the cost for CZT gamma-ray spectrometers has decreased. Unfortunately, because of deficiencies in the quality of the material, high-resolution CZT spectrometers are still limited to relatively small dimensions (< 1 cm3), which makes them inefficient at detecting high photon energies and somewhat ineffective for weak radiation signals except in near proximity. Despite the current constraints on efficiency of the devices, CZT detectors have been increasingly deployed in medical, space, environment, and national security applications for monitoring and imaging radiation in the energy range of 2-2000 keV. The detectors could be attractive for a much broader range of applications; however, increases in their efficiency are needed without sacrificing the ability to spectrally resolve X-ray and gamma energies. Achieving the goal of low-cost efficient CZT detectors requires progress in the following areas: growth of larger crystals, reductions in carrier trapping, increases in the electrical resistivity, better uniformity of device response, and improved device fabrication procedures. This talk will summarize the material factors limiting the performance of CZT gamma-ray detectors and discuss ways to overcome them through appropriate corrections in the crystal growth and device fabrication processes.

The need to harness advanced sensor technology to detect chemical, biological, radiological and nuclear, and explosives (CBRNE) agents is now in vivid focus. This presentation discusses Brookhaven National Laboratory’s new sensor approaches designed to obtain and deliver fast and accurate information to intercept CBRNE materials and respond to a variety of homeland security threats. The talk will cover basic research related to the development of advanced detector materials, applied development of prototype instruments, and the deployment of technology in real-life environments.