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Compton scatter imaging (CSI) is a promising, noninvasive imaging technique; however, it is limited by its poor utilization of X-rays and its bad image signal-to-noise ratio (SNR). In this work, a novel method combining push-broom CSI with coded-aperture imaging was devised to improve the utilization of backscattered X-rays and the image SNR. Firstly, the principles of coded-aperture push-broom CSI are illustrated, and its various applications are discussed. Then, simulations of a point source and a line source are performed to validate its feasibility. It was discovered that the inherent coding noise trends for the mask and the antimask were the opposite of each other. Therefore, these coding noises could be offset by averaging the two. Furthermore, a system prototype was built to scan objects, such as point phantoms, line phantoms, character phantoms of “IHEP”, and other typical samples. Compared with traditional push-broom CSI, this novel system obtained a better backscatter image with lower X-ray power and at a farther distance. This feature is important for system miniaturization and radiation dose reduction. Although optimizations should be considered in the future, this approach demonstrates useful application potential.

Various design of 2-D time-encoded aperture system was investigated for both gamma and neutron imaging. The advantage of time-encoded imaging system for localization of radiological sources relies on its 360-degree horizontal field of view (FOV). Based on the previous report on the two-dimensional time-encoded imager (2D-TEI) for fast neutron, we have developed more attracting TEI systems also effectual for gammaray imaging. In this paper, three TEI systems with different encoding methods and configurations of detector and rotating mask will be demonstrated via Monte Carlo simulation. Lots of radiation scenes support that all these systems have an imaging capacity of multipoint and extended gamma/neutron sources. It is recommended that these designs will provide an alternative panoramic imaging way of search and localization of radioactive hot spots.

Soldier Radio Waveform (SRW) network is a kind of mobile Ad hoc network. It is mostly suitable to tactical or emergency communications. The Time Division Multiple Access (TDMA) control mechanism of Barrage Relay Network (BRN) is used in SRW. To make simulation study on BRN, a group of network models, node models, and process models of BRN are built with OPNET simulation kits. Moreover, the simulation study includes Controlled Barrage Region (CBR), which is a representative application of BRN. The procedures of building CBR and data transmission are implemented. The correctness of these models is proved by extensive simulation experiments and rigorous analyses. These models can be used in both academic study and industrial applications.

This paper presents a coded aperture method to remotely estimate the radioactivity of a source. The activity is estimated from the detected counts and the estimated source location, which is extracted by factoring the effect of aperture magnification. A 6mm thick tungsten-copper alloy coded aperture mask is used to modulate the incoming gamma-rays. The location of point and line sources in all three dimensions was estimated with an accuracy of less than 10% when the source-camera distance was about 4 m. The estimated activities were 17.6% smaller and 50.4% larger than the actual activities for the point and line sources, respectively.

Uranium enrichment measurement is an essential quality inspection for fuel rods before delivery to users. Generally, compared with active neutron assay (ANA) equipment, passive gamma-ray assay (PGA) equipment is more economical and safer. However, the current PGA equipment based on photomultipliers is too slow (1 m/min) to meet the growing needs in China. Recently, we have developed a set of compact high-speed PGA equipment including four detection modules (128 units in total), a 128-channel data acquisition system (DAS), a power supply, special software, and an automatic loading and unloading mechanism. The detection unit is based on silicon photomultipliers in virtue of its compact size and good performance. The DAS processes signals of all units in parallel into a sequence of data packets carrying the energy information and the corresponding unit ID. The software integrates the data packets into a fluctuating count curve in a time-delay superposition method and identifies possible abnormal pellets. After calibrations, our equipment can locate abnormal pellets accurately at a speed of 6 m/min. In addition, it can directly measure the enrichment of fresh pellets not in secular equilibrium without waiting for two months. So far, the equipment has been successfully run for one year on the assembly line of China North Nuclear Fuel Co. and shows good potential to replace the traditional ANA equipment.

Recently, we have devised a novel method called coded aperture push-broom Compton scatter imaging (CAPCSI) to improve the use of backscattered X-rays. Based on a correlation algorithm, near-field artifacts are obvious in the CAPCSI, although they could be reduced partially by averaging dual acquisitions of a mask and an antimask. In this paper, we introduce a maximum-likelihood expectation–maximization (MLEM) algorithm into the CAPCSI to improve the artifacts without dual acquisitions. First, a theoretical system matrix (SM) and a simulative SM were derived from the generation of near-field artifacts. Then, simulation for ideal sources was carried out to compare different algorithms of the correlation and the MLEM. Further, a CAPCSI prototype was set up to confirm the simulation. Because of the system nonuniformity, an experimental SM was derived in advance by a ray-driven way. Finally, imaging for character phantoms was presented. Preliminary results showed the MLEM performed much better for the point source and could obtain a cleaner background for complex objects than the correlation. In the simulation, the theoretical SM and the simulative SM were no essential difference. However, in the experiment, the experimental SM performed essentially better than the theoretical SM, because it took the near-field effects and the system nonuniformity into a comprehensive consideration. This work will help enhance the application potential of the CAPCSI.

Neutron localization, which finds (localizes) neutron sources , is a non-destructive method used in the application of nuclear emergency response and special nuclear material (SNM) localization. Fast neutrons from SNM fission can be detected using a hydrogen-rich scintillation detector system with relatively high efficiency. In this study, we proposed a compact multi-pixel photon counter (MPPC)-based neutron scattering camera prototype consisting of sixteen plastic scintillator pillars. This camera is capable of detecting fast neutrons produced by neutron sources in the far-field. It provides a three-dimensional structure to detect incident neutrons with omnidirectional (4 π ) field-of-view. Based on double neutron–proton elastic scattering, a reconstructed image can be achieved by using an Am–Be source. Besides, time-of-flight technology was adopted for separating neutron signals from the gamma-ray background radiation. The results of the imaging efficiency and the average imaging resolution are reported in this article. This camera offers good prospects to expand the application field of SNM localization for nuclear security and proliferation deterrence.

A new signal readout method for position-sensitive multi-output detectors, such as those in high-energy spectroscopy measurement and nuclear imaging, was developed by combining the charge division circuit, summing circuit and charge-to-time conversion (QTC) circuit. The 64 outputs of a Hamamatsu H8500 position-sensitive photomultiplier tube were processed, and three digital pulses were generated. The widths of digital pulses were determined using the time-to-digital converter in an field programmable gate array. The energy and position information of incident γ-rays is estimated based on the proportionality between the width of digital pulses and input charge created by γ-photons. A prototype was built using discrete components and tested, and the energy and position resolutions were improved compared with that obtained with standard ADCs. This method greatly simplifies the front-end electronics and the digital interface. It enables a compact electronics system and an easy integration into an ASIC.

An instrument used for measuring multiple scintillators' light output and energy resolution was developed. The instrument consisted of a light sensor array which was composed of 64 discrete SiPMs (Silicon Photomultipliers), a corresponding individual channel readout electronics system, and a data processing algorithm. A Teflon grid and a large interval between adjacent SiPMs were employed to eliminate the optical cross talk among scintillators. The scintillators' light output was obtained by comparing with a reference sample with known light output. Given the SiPM temperature dependency and the difference among each SiPM, a temperature offset correction algorithm and a non-uniformity correction algorithm were added to the instrument. A positioning algorithm, based on nine points, was designed to evaluate the performance of a scintillator array. Tests were performed to evaluate the instrument's performance. The uniformity of 64 channels for light output measurement was better than 98%, the stability was better than 98% when temperature varied from 15 °C to 40 °C, and the nonlinearity under 511 keV was better than 2%. This instrument was capable of selecting scintillators and evaluating the packaging technology of scintillator arrays with high efficiency and accuracy.