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Neutron scatter cameras (NSCs) are a type of directionally
sensitive neutron detector that rely on two consecutive neutron
scattering events to localize a source of neutrons. NSCs can be
used to locate, image, and identify unknown neutron sources or
verify the geometry and identity of known sources. Much technical progress has been made in improvin...
Citations
... In many cases, these orphan sources are never recovered, due in part to inadequate radiation detection tools that can be used to swiftly locate and secure them. The high frequency of these incidents and the danger Detection systems devised to provide spatial source information include radiation imaging detectors such as coded aperture systems [6,7], Compton scatter cameras [8], neutron scatter cameras [9], and time projection chambers [10]. Compact, mobile designs of these systems have been demonstrated in source searching applications, but the required high particle flux can limit the range of in-field applications for these systems. ...
The ability to detect, localize, and characterize special nuclear material (highly enriched uranium and plutonium) is important for nuclear security, safeguards, nonproliferation, and weapons dismantlement verification. In these fields, particle imagers and systems that are sensitive to both gamma rays and neutrons can prove vital because the special nuclear material of interest will often emit both types of particles. The presence and detection of neutrons serves as an important marker because they are not as easily attenuated; gamma rays can offer strong identification information through spectrometry. We have developed a new compact scatter-based imager prototype that utilizes organic glass scintillators of novel composition and CeBr 3 scintillators to image both gamma rays and fast neutrons. We present new results demonstrating that the instrument is capable of imaging single and multiple gamma/neutron sources in the same field of view. We also show that the organic glass scintillator-based imager can perform coarse neutron and gamma-ray spectrometry, further enabling source characterization. This instrument has potential to aid in security, safeguards, and verification scenarios.
We demonstrate the ability to obtain the direction of the gamma rays using a standard coaxial high purity germanium (HPGe) detector using the direction-sensitive information embedded in the shape of the pre-amplified HPGe signals. We deduced the complex relationship between the shape of the signal and the direction from which the gamma-ray enters the detector active volume using a two-step machine learning technique. In the first step, we collected pulses from the HPGe detector due to a 133Ba radioactive source placed in four distinct positions around the detector while keeping the distance from the center of the detector crystal constant. A subset of the pulses collected with radioactive source kept at the four positions was used to train an artificial neural network (ANN) called a self-organizing map (SOM) to cluster the HPGe waveforms based on their shape. The trained SOM network was then utilized to produce direction-specific maps corresponding to pulses generated when the 133Ba source is at a specific location with respect to the detector. In the second step, we used the SOM-generated direction-specific maps to train another network composed of a single feedforward layer for predicting the direction of the gamma ray from the pulses produced by the HPGe detector due to the gamma energy deposition. Our results show that even without employing complex methodologies, a standard coaxial HPGe detector can estimate the direction of incoming gamma rays and thus, provide initial guidance on the gamma-emitting radioactive source direction with reference to the detector.
The development of compact and portable neutron imagers could be transformative for nuclear nonproliferation and security. Of the currently feasible neutron imaging concepts, the neutron scatter camera is the one that can be made most compact and versatile. Beneficially, this design also inherently measures the energy of incident neutrons on an event-by-event basis. Single volume and quasi-single volume neutron scatters have been proposed to fully maximize the potential of neutron scatter cameras and enable truly man-portable neutron imagers. Such imagers will likely have a very large number of readout channels to maximize the efficiency, so signal multiplexing to reduce readout channels would significantly reduce costs and size and facilitate wide-spread deployment. In this work a multiplexing method based on adding well-defined sinusoids to detector signal is applied to a quasi-single volume neutron scatter camera comprised of 6-mm x 6-mm x 60-mm EJ-299-34 plastic scintillators coupled to arrays of SensL 60035 C-series silicon photomultipliers to create a multiplexed neutron imager (MiNI). Such straightforward multiplexing enables the use of more detector elements for a given number of available signal readouts. The necessary calibrations and system characterizations are carried out to assess the multiplexing method’s performance and to understand the behavior of the prototype MiNI. Its ability to successfully image a neutron source is demonstrated with a ²⁵²Cf spontaneous fission source placed in various locations around the MiNI. Finally, neutron spectroscopy is also performed, and the feasibility and benefits of multiplexing a quasi-single volume neutron scatter camera are demonstrated.
