This study presents a technique to enhance Compton camera imaging used for radioactive source localization in security applications. A key issue in Compton imaging is "backscattering events," where gamma-ray interactions are misordered—such as when the absorber records a hit before the scatterer—leading to incorrect Compton cone reconstruction and image artifacts. To address this, the research applies the Time-of-Flight (TOF) principle to determine the correct interaction sequence.A detector system comprising GFAG scintillators, SiPMs, and a custom ASIC/DAQ setup achieves a 296 ps coincidence time resolution, sufficient to resolve 4.4 cm-scale interaction order. TOF values are calculated per event after correcting for systematic effects, allowing identification and rejection of backscattering events. Applying this TOF-based filtering significantly improves the signal-to-noise ratio. The resulting data, processed with the MLEM algorithm, yields an angular resolution (ARM) of 13.3°–16.5° (FWHM), aligning well with Geant4 simulations. This demonstrates TOF filtering as an effective method for enhancing Compton imaging quality.

The development of non-destructive assay techniques for minor actinides is of significance for ensuring nuclear security and safeguards worldwide. Therefore, we previously proposed an active gamma-ray method, named the photon-induced multiple neutron generation reaction ratio (PMNRR) method. This study is aimed at demonstrating the feasibility of detecting Am based on photonuclear reactions through numerical analysis simulations. The applicability of the PMNRR method for separated Am is examined, revealing the optimal combination of incident photon energies for discriminating each nuclide. Subsequently, the potential for detecting Am in uranium fuel and estimating its isotopic composition ratio is investigated, clarifying the lower detection limits of Am and required uncertainties in nuclear data. Nuclear data uncertainties of 3.13 %, 2.15 % and 1.77 % were required to detect 5.0 wt% of 241Am, 242mAm and 243Am in UO2 fuel, respectively. The findings demonstrate the potential applicability of the PMNRR method for the detection and verification of Am.

Various types of physical evidence remain at crime scenes, and if they can be identified, they become crucial evidence. Traditionally, identification involves the application of chemical reagents and observation of the reactions. However, this method carries the risk of sample contamination. Therefore, we conducted experiments using hyperspectral imaging (HSI) to non-destructively visualize and identify industrial materials in various forensic samples collected from crime scenes. The object materials included automobile windshields and ignitable liquids. A powdered synthetic resin was prepared as a mixed sample. Measurements were performed using a near-infrared hyperspectral camera. HSI of 14 types of car windshield glass revealed slight spectral differences between them. Therefore, hierarchical clustering was performed, and the samples were separated into three groups. The correlation coefficients were obtained using three representative glasses as references and allocated to the R, G, and B color images, allowing the images to be displayed in color for visual clarity. However, forensic materials are often mixed in the field. HSI of a mixture of three types of powdered synthetic resins was performed to investigate the possibility of separating the mixed samples. As a result, when displayed in pseudo-color at three wavelengths, it was possible to distinguish the compositional elements in the case of a low degree of mixing. Furthermore, independent component analysis enabled the separation of the three synthetic resins, even in a highly mixed sample.

We developed a technique for visualizing organic gunshot residue (OGSR) dispersed on a strongly fluorescent background by applying hyperspectral imaging (HSI) for criminal investigation. Test shots were obtained using several kinds of cartridges against a white cotton towel at a shooting distance of 5 to 10 cm. A sample in which OGSR existed around the bullet entrance was prepared and scanned using HSI. An excitation wavelength of 415 nm was selected as the condition under which the background emitted strong fluorescence. In this condition, the short-wavelength band (450 to 500 nm) hindered the visualization of OGSR. We proposed the normalization of a hyperspectral cube (HSI data format) to the wavelength direction for clearly visualizing the OGSR when the background has strong fluorescence. Particle analysis was performed on the OGSR visualized using HSI, and the OGSR spectra were extracted. The method developed in this study enhanced the utility value of OGSR by overcoming potential problems in actual crime investigations involving background fluorescence. This study is relevant to the literature because the method could be potentially applied to the next step such as the prediction of cartridges used in a crime scene in the future.

Lead-free cartridges have significantly impacted forensic firearm investigation in Japan. Traditional methods cannot determine shooting incidents involving lead-free cartridges because the inorganic gunshot residue (IGSR) they produce lacks the distinctive particles required for identification. To address this challenge, we developed a classification method based on comprehensive elemental characteristics and demonstrated that lead-free cartridges possess unique features compared to conventional cartridges. IGSR was collected after test-firing ten types of cartridges, and visualization and elemental analysis were conducted using an electron probe microanalyzer. To better understand IGSR characteristics, we successfully applied correlation analysis combined with principal component analysis (PCA). In conclusion, this study demonstrates that cartridge types can be classified by analyzing the overall elemental composition of IGSR. Therefore, the proposed method is expected to be useful for identifying lead-free cartridges.

A prototype system based on a combination of 4π sensitive gamma imaging and simultaneous localization and mapping (SLAM) was developed to find unknown radiation source(s) rapidly. The system consisted of a spherical visible camera, a three-dimensional light detection and ranging, a CdTe pixel array detector for 4π gamma imaging, a portable battery, and a control laptop personal computer; these were mounted on an unmanned vehicle. In a search area of 16 × 16 m 2 with a height of 3 m, the prototype system successfully demonstrated the finding of a 137 Cs point source with an activity of 0.67 MBq in the surrounding thin walls.

The global challenge of on-site detection of highly enriched uranium (HEU), a substance with considerable potential for unauthorized use in nuclear security, is a critical concern. Traditional passive nondestructive assay (NDA) techniques, such as gamma-ray spectroscopy with high-purity germanium detectors, face significant challenges in detecting HEU when it is shielded by heavy metals. Addressing this critical security need, we introduce an on-site detection method for lead-shielded HEU employing a transportable NDA system that utilizes the 252Cf rotation method with a water Cherenkov neutron detector. This cost-effective NDA system is capable of detecting 4.17 g of 235U within a 12 min measurement period using a 252Cf source of 3.7 MBq. Integrating this system into border control measures can enhance the prevention of HEU proliferation significantly and offer robust deterrence against nuclear terrorism.

Latent fingerprints were successfully visualized using fluorescence lifetime imaging (FLIM) on paper which emits strong fluorescence with a lifetime close to that of fingerprints and thus from which it is difficult for time-resolved spectroscopy to visualize fingerprints. Latent fingerprint samples on paper were excited using a 450 nm or 532 nm nanosecond pulsed-laser, and time-resolved fluorescence images were obtained at a delay time of 6-16 ns in intervals of 1 ns, to the excitation pulse. The excitation beam was expanded using a lens, and the fluorescence from the fingerprints was captured using an intensified CCD camera. Because of the large fluorescence intensity of the background paper of approximately two to four orders of magnitude larger than that of the fingerprint, the fingerprint was not visualized on each fluorescence image by time-resolved spectroscopy. However, the fingerprint was visualized in a FLIM image constructed using a series of the fluorescence images for the case with the fluorescence intensity of the background paper being four orders of magnitude larger than that of the fingerprint. The difference in fluorescence lifetime in the FLIM image of the visualized fingerprint and background paper was in the order of 0.1 ns, which was an order of magnitude smaller than the inherent fluorescence lifetime of a few nanoseconds for the fingerprints and paper. It was demonstrated that, at a background fluorescence intensity with a certain order of magnitude larger than that of fingerprints, FLIM has the potential to visualize latent fingerprints which cannot be visualized by time-resolved spectroscopy.

Radioisotope finding method is required to prevent terrorist acts using radioactive source(s) and to find lost or stolen radiation source(s). For operators’ safety, it is desirable to use an unmanned system with remote operation. Therefore, we are developing a prototype system using a 4π gamma imager and a 3D-LiDAR mounted on an unmanned vehicle for simultaneously performing gamma-ray imaging and recognition of surrounding structures. Finding of a high-intensity 137Cs gamma point source located at 70 m square field was demonstrated experimentally based on fusion data between 4π gamma images and 3D-LiDAR-SLAM obtained by the prototype system.

The active neutron method is a highly effective approach for nuclear security, enabling the detection of nuclear materials by irradiating the object with neutrons and measuring the fission neutrons. This method has proven particularly effective for detecting highly enriched uranium, which is challenging to identify with passive neutron and gamma methods. However, distinguishing between irradiated neutrons and fission neutrons requires a special technique, such as using pulsed neutron irradiation. The DDA method and FNDI method are well-known for active neutron techniques using pulsed neutrons. However, those methods have the drawback of relying on expensive accelerators. Besides devices using accelerators have a disadvantage of the rather massive. Since those disadvantages prevent the devices’ widespread use, we have been developing a new method and device, which satisfies low-cost and transportable, for nuclear security. To address these challenges, we have developed a novel technique called the active rotation method, which utilizes a rotating neutron source near the object being measured to detect nuclear materials. The device to rotate a neutron source can be produced at low-cost and it is compact. A neutron source is rotated with several thousand rpm at measuring, and it is possible to detect nuclear materials by confirming the deformation of the time-distribution spectrum obtained by a neutron detector. In addition to the rotation device, we have also developed a low-cost neutron detector utilizing water Cherenkov radiation. Our presentation will introduce this newly developed a rotation device and demonstrate its nuclear material detection capabilities.

The photon-induced multiple neutron generation reaction rate ratio (PMNRR) method is a novel active gamma-ray method that detects fissionable materials based on the photonuclear reaction rate ratio. In the present study, the feasibility of detection of 241 Am by the PMNRR method was verified using numerical analysis simulations. As a result, the separated 241 Am could be discriminated from 237 Np, 235 U and 238 U using the PMNRR with the optimal combination of incident photon energies, even if a 10% uncertainty was considered in the nuclear data of the (γ, fission/2n) reaction. In addition, the prospect of estimation of Am composition ratios in UO 2 using PMNRR was also obtained.

The active rotation method is an innovative, transportable, active neutron method suitable for on-site detection of concealed nuclear material. Its assay system consists mainly of a neutron detector and a rotation device for rotating a neutron source such as californium-252. Although we previously demonstrated a low-cost rotation device, the neutron detector bank comprising helium-3 proportional counters was extremely expensive and had low detection efficiency, leaving the challenges of reducing cost and measurement time. In the present study, we developed a water Cherenkov neutron detector as a novel neutron detector for the active rotation method and demonstrated its suitability and effectiveness for nuclear material detection, meeting the cost, efficiency, and transportability criteria for nuclear security.

A principle of new nondestructive assay (NDA) technique based on the photofission reaction ratio (PFRR) has been developed, which is aimed at measuring the isotopic composition of nuclear fuel materials without relying on their self-generated neutron information. The feasibility of the PFRR method was validated in the 235U-238U system previously. However, applicability of the PFRR method in the other material is not yet validated. In this study, applicability of PFRR method to the 232Th-233U system was confirmed, PFRR method showed good reproducibility of predicted value of 232Th and 233U isotopic composition.

For accurate identification of radiation sources using 4π gamma imaging, the selection rule of measurement points around target sources was investigated. In a simple computational model of the 4π gamma imaging, the detector movement algorithm was optimized by decision trees analysis. According to the proposed algorithm, a 137Cs point source was identified using a multi-pixel CdTe detector mounted on an unmanned vehicle as a prototype 4π gamma imager.

Fingerprints provide important clues to criminal investigations. Although there are various fingerprint detection methods such as powder or liquid, optical methods are useful for non-contact and non-destructive detection. However, in case of two or more overlapping fingerprints, they might be discarded because the features cannot be assigned to the individual fingerprints. The fact that the composition of fingerprints is unique for each individual is well known, so if this causes differences in inherent emission spectra of fingerprints, it is possible to separate overlapping fingerprints. Hyperspectral imaging is used in a variety of fields and also in forensic science, such as fingerprint detection. In this study, the separation of overlapping fingerprints using multivariate analysis was performed for effective use of fingerprints. Fluorescence hyperspectral data of overlapping fingerprints excited by a 532 nm CW laser were acquired by hyperspectral imaging in the visible region. Fluorescence spectra from fingerprints were measured in the wavelength range from 560 to 700 nm with the wavelength resolution of 1.1 nm. Thus, the hyperspectral data cube consisted of 600 (image) × 960 (image) × 128 (wavelength) pixels. An image, which are integrated over the wavelength range, showed the two fingerprints overlapping each other. Separation of overlapping fingerprints was tried applying principal component analysis, multivariate curve resolution - alternating least squares analysis, and partial least squares analysis to the fluorescence hyperspectral data. Among three methods examined herein, partial least squares analysis was found to be most effective for fingerprint separation.

This paper presents a novel method for the detection of Np-237 in its separated form and advanced fuel by applying the principle of the photofission reaction ratio (PFRR). In this method, Np-237 was identified using the photon-induced multiple neutron generation reaction rate ratio (PMNRR) with multiple high-energy gamma rays. The feasibility of the discrimination between the separated Np-237 and uranium (U-235, U-238) and the detection of the Np-237 above a certain composition ratio in UO2 was examined by numerical analysis simulation. The proposed method has a wide range of incident photon energy selectivity because it utilizes the (*, 2n) reaction, which is considered an inevitable measurement obstacle in the PFRR method. The results show the detectability of Np-237 even with a 10% uncertainty in the nuclear data of the (c, fission/2n) reaction, and the robustness of the PMNRR method to the energy distribution of incident pho-tons. In the future, the proposed method is expected to be applied for detection and verification in the field of nuclear non-proliferation and security. (c) 2022 Elsevier Ltd. All rights reserved.

Compton camera is a radiation detector that uses the kinematics of Compton scattering to estimate the direction of the gamma-ray incident. Compton camera has been used in many applications such as astronomy, medical, nuclear industry, and security. High time resolution in a Compton camera is essential to distinguish the incoming event in the detector. In this work, we developed a Compton camera using a fast decay scintillator and a high time resolution front end circuit to get a high-performance detector. The detector used an 8×8 multi-pixel photon counter (MPPC) array, which individually couple with a 2.5×2.5×5 mm3 GFAG (Gadolinium Fine Aluminum Gallate) scintillator. For processing the analog signal from the MPPC scintillators, the 64 channel ASIC (Application-Specific Integrated Circuit) is used. Each channel in the ASIC circuit consists of a pre-amplifier, shaper, monostable multivibrator, and slew-rate time over threshold. The ASIC will provide the digital output signal that contains the timing and energy information. The high-time resolution data acquisition circuit (PETnet) based on FPGA is used to acquire energy and time data from ASIC.