The SORDS trimodal imager detector arrays

Abstract

The Raytheon Trimodal Imager (TMI) uses coded aperture and Compton imaging technologies as well as the nonimaging shadow technology to locate an SNM or radiological threat in the presence of background. The heart of the TMI is two arrays of NaI crystals. The front array serves as both a coded aperture and the first scatterer for Compton imaging. It is made of 35 5x5x2" crystals with specially designed low profile PMTs. The back array is made of 30 2.5x3x24" position-sensitive crystals which are read out at both ends. These crystals are specially treated to provide the required position resolution at the best possible energy resolution. Both arrays of detectors are supported by aluminum superstructures. These have been efficiently designed to allow a wide field of view and to provide adequate support to the crystals to permit use of the TMI as a vehicle-mounted, field-deployable system. Each PMT has a locally mounted high-voltage supply that is remotely controlled. Each detector is connected to a dedicated FPGA which performs automated gain alignment and energy calibration, event timing and diagnostic health checking. Data are streamed, eventby-event, from each of the 65 detector FPGAs to one master FPGA. The master FPGA acts both as a synchronization clock, and as an event sorting unit. Event sorting involves stamping events as singles or as coincidences, based on the approximately instantaneous detector hit pattern. Coincidence determination by the master FPGA provides a pre-sorting for the events that will ultimately be used in the Compton imaging and coded aperture imaging algorithms. All data acquisition electronics have been custom designed for the TMI.

Self-occluding quad NaI directional gamma radiation detector for standoff radiation detection

“…In addition to these advantages, the detector also has a 360° field of view. While the detection performance of a 3x3x12 inch NaI based system for small sources in large background radiation is not as good as the expected performance of the coded-aperture/Compton imaging SORDS systems [1][2] [3], they are significantly less expensive, less complex, and more compact and more readily deployed. One may deploy many of these systems for the cost of a single coded-aperture/Compton imaging system.…”

“…The problem is made even more difficult for mobiles radiation detection systems, particularly in urban environments, where very large deviations in background count rates are common. Gamma-ray imaging is one technique that has been used to over come the issues associated with large background variations [1][2] [3]. The imaging is used to reduce the signal from the more distributed background radiation to locate more concentrated sources.…”

Utilization of advanced clutter suppression algorithms for improved standoff detection and identification of radionuclide threats

“…TMI has been described in detail elsewhere. 6 Briefly, the core of the TMI design employs two detector arrays. The front array is a coded aperture mask with active NaI detectors in the blocked areas of the mask.…”

“…as the Standoff Radiation Detection System (SORDS) 6 that incorporates more sensitive detectors. The PCS algorithm was developed to accurately mitigate both sources of randomness in the radiological spectra by combining an accurate model of the Poisson processes and an efficient representation of background clutter within a single probabilistic framework.…”

First demonstration of a Compton gamma imager based on silicon photomultipliers

“…Nevertheless, the capabilities of solid scintillator in terms of energy resolution, high efficiency, ruggedness and affordability has warranted its investigation for use in the scatter detector [8,9]. Compton gamma imagers have been demonstrated which employ inorganic scintillator in the scatter layer with either conventional photomultiplier tube (PMT) readout in the path of the incoming gamma ray [10] or with a novel scintillator bar concept such that the PMTs can be located at the side of the detector, out of the gamma-ray path [11].…”