BACKGROUND:  Current gamma-ray detectors use one of two main types of detection media, either scintillators or solid-state detectors. Scintillators convert gamma-rays to low energy photons, which are detected by photomultiplier tubes, but overall the entire system can be rather bulky. Solid-state technologies, based on semiconductor materials, provide a more compact design, and lower noise, with enhanced energy and spatial resolution compared to scintillators. However, the high Z semiconductor materials necessary for gamma-ray absorption have small energy band gaps, which results in large leakage currents. To overcome this, materials like germanium have to be operated at cryogenic temperatures, which adds significant infrastructure to the system. Additionally, complete charge collection in solid-state materials requires very low ionized impurity concentrations, which adversely affect the detector response time, energy resolution, operation voltage, and portability.

INNOVATION:  This novel design invention is based on a composite layered structure that offers the benefits of high Z gamma-ray absorption combined with excellent charge collection in a much smaller package, which leads to significant improvements on the overall detector performance. The design also enables room temperature operation under reduced voltage, and promises improved energy resolution.

POTENTIAL APPLICATIONS 

• Room temperature semiconductor-based gamma-ray detection for medical imaging
• Radioactive material cargo screening for homeland security
• Interstellar gamma-ray detection for space science

ADVANTAGES

• Provides near 100% absorption of gamma-rays up to several MeV in energy
• Higher linear attenuation coefficient eliminates need for semiconductors to be centimeters thick
• Shorter carrier transit time, lower bias voltage, immunity to carrier trapping, better resistance to radiation damage
• Signal-to-noise ratio for the detector can be optimized for room temperature operation
• Enables high resolution detection with an order-of-magnitude lower bias voltage
• Resists radiation damage by maintaining immunity to carrier trapping

Reference: UCLA Case No. 2007-003