The detection of radiological and special nuclear material within the country's borders is a crucial component of the national security network. Being able to detect small amounts of radiological material at large distances is especially important for search applications. To provide this capability General Electric's Research Center has developed, as a part of DNDO's standoff radiation detection system advanced technology demonstration (SORDS-ATD) program, a standoff radiation imaging system (SORIS). This vehicle-based system is capable of detecting weak sources at large distances in relatively short times. To accomplish this, GE has developed a novel coded aperture detector based on commercial components from GE Healthcare. An array of commercial gamma cameras modified to increase the system efficiency and energy range are used as position sensitive detectors. Unlike typical coded aperture systems, however, SORIS employs a non-planar mask and thus does not suffer the typical limitations of partially encoded regions giving it a wide field of view. Source identification is done using both low-statistics anomaly indicators and conventional high-statistics algorithms being developed by Pacific Northwest National Laboratory. The results of scanned areas and threats identified are displayed to the user and overlaid on satellite imagery.

The solid state photomultiplier (SSPM), an array of Geiger-mode APDs, developed by Hamamatsu Corp. has been evaluated for time-of-flight PET detectors. As it was demonstrated in previous work the SSPM is a promising photo sensor to achieve very good timing resolution for PET applications. Due to relatively small size of individual sensor (3×3 mm2) a large number of readout channels will be required in applications such as a whole body PET scanner. The obvious solution for this problem is multiplexing several devices into a single readout channel. To better understand the limits and trade offs involved for timing resolution a detailed analysis of the effects of dark current, amplifier noise, bandwidth and amplifier input impedance was done.

Silicon carbide (SiC) separate absorption multiplication region avalanche photodiodes (SAM-APDs) for UV detection in harsh environment applications were designed and fabricated. The devices were intentionally designed to operate under nonreach-through conditions in order to eliminate field-induced leakage current. The gain of 2500 and quantum efficiency of similar to 45% at room temperature were achieved at the wavelength of 290-300 turn for a packaged device with an active area of 1 x 1 mm(2). The temperature dependency of the current-voltage characteristics and responsivity was examined in the temperature range front room temperature to 230 degrees C.

Radiation damage of amorphous silicon X-ray imagers leads to degradation of the detector's performance due to increased diode perimeter leakage. To reduce the effect of this damage, a novel pixel device based on a gated diode was fabricated. The additional gate metalization placed on the perimeter of the diode modulates the surface side-wall leakage and has been tested up to a 64 kGy absorbed dose in the diode. This new pixel design significantly reduces the increase in diode leakage and noise due to radiation damage, providing a more uniform performance and extending the lifetime of the imager.

We report on the design of a neutron detector using industry standard 3He tubes to count delayed neutrons during the interrogation of cargo containers for the presence of Special Nuclear Material (SNM). Simulations of the detector design were run for delayed neutron spectra for a variety of cargos containing SNM using the Monte Carlo computer code COG. The simulations identified parameters crucial to optimize the detector design. These choices include moderating material type and thickness, tube spacing, tube pressure and number of tubes. An experimental prototype was also constructed based on the simulated design specifications. This paper discusses the parameters that lead up to the optimized detector design. It also compares the performance of the Monte Carlo simulated design and the experimental detector when exposed to a 239Pu-Be source.

We designed and fabricated silicon carbide (SiC) separate absorption multiplication region avalanche photodiodes (SAM-APDs) for UV detection in harsh environment applications. Two variations of device types were compared. Type I was designed to achieve reach-through (i.e. multiplication, charge, and absorption layers are depleted) prior to reaching high gain while Type II was designed not to achieve reach-through (i.e. only the multiplication region is depleted). It was found that both the dark current behavior and the responsivity were improved significantly by employing a nonreach-through design. According to preliminary measurements, the maximum quantum efficiency of the type II was ~70 % at the wavelength of 300 nm.