SBIR-STTR Award

Space-based gamma ray observatories are important for detection of nuclear explosions as well as for astrophysics research. A new generation of gamma ray sensors is needed that can accurately detect, locate, and identify nuclear explosions in the high-intensity background radiation of space, and operate for many years. Europium-doped strontium iodide (SrI2:Eu) is a halide scintillator with the potential to supersede older detector materials due to its ruggedness, radiation hardness, absence of internal activity, high sensitivity, lower cost, excellent linearity, high energy resolution in the entire energy range, and its recent successful space flight demonstration. This program will develop miniaturized SrI2:Eu detectors with integrated solid-state readout and signal processing electronics that are qualified for space-based applications. When connected together to form an array, the sensor modules will form a mesh communication network. The purpose of this network is to enable radiation source localization through analysis of Compton scattering events, cooperative accumulation of energy spectra, and reduction of the effect of background radiation. Redundant accumulation of the data in all array elements will allow any module to communicate the telemetry output, providing resilience against module failures. Phase I will demonstrate feasibility of this concept by developing working prototypes of the sensor modules that are capable of interlocking and networking to share information. Phase I will also validate the performance in space through Monte Carlo simulations on a model of a full array. While Phase I development will focus on SrI2:Eu, we anticipate that the technology developed by the program will be applicable to other scintillation materials, such as elpasolites that are sensitive to both gamma rays and neutrons. Phase II will develop the Compton imaging and radioisotope identification capabilities of full arrays. The proposed research program will advance progress towards a new generation of smaller, lower-cost, higher-performance, space-based sensor arrays for nuclear detonation detection, localization, and radioactive residue identification, through improved gamma ray spectroscopy.

Spacebased sensors for detecting nuclear weapon detonations and radioactive residues are critical to national security and nuclear nonproliferation. A compact sensor module for the next generation of monitoring systems is being developed to provide high energy resolution to detect, identify, locate, and track gamma ray emissions over a wide energy range. These sensors provide benefits in size, weight, power utilization, computational sophistication, and cost that will allow them to be deployed on hundreds of small satellites. Prototype sensor modules were designed and built in Phase I, based on europiumdoped strontium iodide and a variety of other scintillators. All of the electronics for light collection, digitization and accumulation of calibrated energy spectra are contained within each sensor module. These prototypes demonstrated the feasibility of lowpower, compact sensor modules capable of sustaining highperformance gamma spectrometry in challenging environmental conditions. When connected together, the prototype sensor modules automatically coordinate to share and combine spectral measurements, before streaming the combined results to a host computer. This interconnection capability is being developed because significant performance enhancements may be obtained by combining the outputs of multiple sensor modules. When modules are combined into an array, the larger detector volume provides increased gamma sensitivity, such that more information is obtained in less time. An array of multiple sensor modules would also be able to estimate the direction of gamma radiation through the selfshielding effect. In Phase I, a generalization of the self shielding effect was developed to allow any arrangement of sensor modules to be easily programmed to locate the source of gamma radiation. Sensor modules will continue to be developed in Phase II, with further miniaturization and integration of the electronics, improvements in temperaturecompensated energy calibration, and faster and more flexible moduletomodule communications. The computational capabilities of the sensor modules will be extended to include background filtering, pulseshape discrimination, and radioisotope identification. Prototypes of sensors arrays containing 12 to 28 sensor modules will be built in Phase II, including implementation and testing of the source direction sensing technique. The reliability of the sensors will be evaluated in Phase II through more extensive environmental testing. This research program will advance progress towards a new generation of smaller, lower cost, higherperformance, spacebased sensor arrays for nuclear detonation detection,localization, and radioactive residue identification, through improved gamma ray spectroscopy. The sensor modules developed in this program can be at low cost with low power consumption for space deployment. Arrays of sensor modules are being designed to fit on very small satellites, such as 3U CubeSats. The proposed sensor modules can