We present the detector response comparison between a 10x10 pixellated array of scintillator read out with Anger logic using four 2" Hamamatsu R7724-100 super bialkali photomulti- plier tubes (PMT) and a custom Silicon photomultiplier (SiPM) board consisting of 100 C-series 6x6 mm SiPMs from SensL. An array of these pixellated detectors are currently used in the Neutron Coded Aperture (NCA) imaging system. The energy, timing and pulse shape discrimination response using both readout schemes are presented, along with an anal- ysis of multiple scatter events occurring within the block. An evaluation of the impact of photodetector readout on the overall detection efficiency and imaging accuracy is presented.
We present the relative timing and pulse-shape discrimination performance of a H1949-50 photomultiplier tube to SensL ArrayX-B0B6_64S coupled to a SensL ArrayC-60035-64P- PCB Silicon Photomultiplier array. The goal of this work is to enable the replacement of photomultiplier readout of scintillators with Silicon Photomultiplier devices, which are more robust and have higher particle detection efficiency. The report quantifies the degradation of these performance parameters using commercial off the shelf summing circuits, and motivates the development of an improved summing circuit: the pulse-shape descrimination figure-of- merit drops from 1.7 at 500 keVee to 1.4, and the timing resolution (a) is 288 ps for the photomultiplier readout and approximately 1 ns for the Silicon Photomultiplier readout. A degradation of this size will have a large negative impact on any device that relies on timing coincidence or pulse-shape discrimination to detect neutron interactions, such as neutron kinematic imaging or multiplicity measurements.
Through a series of measurements with a high purity germanium detector, we have established that the past presence of neutron emitting material can be detected by the decay of activation products in aluminum containers, tungsten shielding, and concrete floors even several days after last exposure. The time since last exposure can also be estimated by the gamma-ray detection rate. These findings may lead to interesting new CONOPS in the detection of illicit SNM or the verification of the absence (or presence) of SNM containing objects in facilities and/or transit even after the material has been removed.
We present single-sided 3D image reconstruction and neutron spectrum of non-nuclear material interrogated with a deuterium-tritium neutron generator. The results presented here are a proof-of-principle of an existing technique previously used for nuclear material, applied to non-nuclear material. While we do see excess signatures over background, they do not have the expected form and are currently un-identified.
We present the design, characterization, and testing of a laboratory prototype radiological search and localization system. The system, based on time-encoded imaging, uses the attenuation signature of neutrons in time, induced by the geometrical layout and motion of the system. We have demonstrated the ability to detect a ∼1mCi252Cf radiological source at 100m standoff with 90% detection efficiency and 10% false positives against background in 12min. This same detection efficiency is met at 15s for a 40m standoff, and 1.2s for a 20m standoff.