Balloon flight test of a CeBr3 detector with silicon photomultiplier readout.

Recent advances in silicon photomultiplier (SiPM) technology and new scintillator materials allow for the creation of compact high-performance gamma-ray detectors which can be deployed on small low-cost satellites. A small number of such satellites can provide full sky coverage and complement, or in some cases replace the existing gamma-ray missions in detection of transient gamma-ray events. The aim of this study is to test gamma-ray detection using a novel commercially available CeBr3 scintillator combined with SiPM readout in a near-space environment and inform further technology development for a future space mission. A prototype gamma-ray detector was built using a CeBr3 scintillator and an array of 16 J-Series SiPMs by ON Semiconductor. SiPM readout was performed using SIPHRA, a radiation-tolerant low-power integrated circuit developed by IDEAS. The detector was flown as a piggyback payload on the Advanced Scintillator Compton Telescope balloon flight from Columbia Scientific Balloon Facility. The payload included the detector, a Raspberry Pi on-board computer, a custom power supply board, temperature and pressure sensors, a Global Navigation Satellite System receiver and a satellite modem. The balloon delivered the detector to 37 km altitude where its detection capabilities and readout were tested in the radiation-intense near-space environment. The detector demonstrated continuous operation during the 8-hour flight and after the landing. It performed spectral measurements in an energy range of 100 keV to 8 MeV and observed the 511 keV gamma-ray line arising from positron annihilation in the atmosphere with full width half maximum of 6.8%. During ascent and descent, the detector count rate peaked at an altitude of 16 km corresponding to the point of maximum radiation intensity in the atmosphere. Despite several engineering issues discovered after the flight test, the results of this study confirm the feasibility of using CeBr3 scintillator, SiPMs, and SIPHRA in future space missions.

Ammonium Fluoride Passivation of CdZnTeSe Sensors for Applications in Nuclear Detection and Medical Imaging.

Cadmium zinc telluride selenide (Cd1-xZnxTe1-ySey or CZTS) is one of the emerging CdTe-based semiconductor materials for detecting X- and gamma-ray radiation at or near room temperature (i.e., without cryogenic cooling). Potential applications of CZTS sensors include medical imaging, X-ray detection, and gamma-ray spectroscopy. Chemical passivation of CZTS is needed to reduce the conductivity of Te-rich surfaces, which reduces the noise and improves the device performance. In this study, we focus on the effect of surface passivation of CZTS using a 10% aqueous solution of ammonium fluoride. The effects of the chemical treatment were studied on the leakage current, charge transport measured as the electron mobility-lifetime (µτ) product, and the spectral resolution measured as the full-width at half-maximum (FWHM) of specific peaks. After passivation, the leakage current increased and began to decrease towards pre-passivation levels. The energy resolutions were recorded for eight applied voltages between -35 V and -200 V. The results showed an average of 25% improvement in the detector's energy resolution for the 59.6 keV gamma peak of Am-241. The electron µτ product was unchanged at 2 × 10-3 cm2/V. These results show that ammonium fluoride is effective for chemical passivation of CZTS detectors.

Integration of Ground- Penetrating Radar and Gamma-Ray Detectors for Nonintrusive Characterisation of Buried Radioactive Objects.

The characterisation of buried radioactive wastes is challenging because they are not readily accessible. Therefore, this study reports on the development of a method for integrating ground-penetrating radar (GPR) and gamma-ray detector measurements for nonintrusive characterisation of buried radioactive objects. The method makes use of the density relationship between soil permittivity models and the flux measured by gamma ray detectors to estimate the soil density, depth and radius of a disk-shaped buried radioactive object simultaneously. The method was validated using numerical simulations with experimentally-validated gamma-ray detector and GPR antenna models. The results showed that the method can simultaneously retrieve the soil density, depth and radius of disk-shaped radioactive objects buried in soil of varying conditions with a relative error of less than 10%. This result will enable the development of an integrated GPR and gamma ray detector tool for rapid characterisation of buried radioactive objects encountered during monitoring and decontamination of nuclear sites and facilities.

A compact scintillator-based detector with collimator and shielding for dose monitoring in boron neutron capture therapy.

Boron neutron capture therapy exploits 10B(n,α)7Li reactions for targeted tumor destruction. In this work, we aimed at developing a dose monitoring system based on the detection of 478 keV gamma rays emitted by the reactions, which is very challenging due to the severe background present. We investigated a compact gamma-ray detector with a pinhole collimator and shielding housing. Experimental nuclear reactor measurements involved varying boron concentrations and artificial shifts of the sources. The system successfully resolved the 478 keV photopeak and detected 1 cm lateral displacements, confirming its suitability for precise boron dose monitoring.

Developing a remote gamma-ray spectra collection system (RGSCS) by coupling a high purity Germanium (HPGe) detector with a cosmicguard background reduction device.

Despite being widely used for high-resolution spectral analysis and quantifying low activity in natural samples, the operations and data analysis of High Purity Germanium (HPGe) gamma-ray detectors are seldom fully automated due to the excessive costs associated with commercially available automatic sample changing systems. This paper introduces the design and implementation of a cost-effective, customized remote gamma-ray spectra collection system centered around the HPGe detector coupled to a cosmic-ray veto background reduction device. The HPGe detector system, equipped with a Lynx DSA, is seamlessly integrated with an economically viable automatic sample changer. This sample vial changer is controlled by a high-torque NEMA 34 stepper servo motor from Vention. Web control of the rotary actuator is facilitated through a CAD-based programming tool. The remote-controlled sample pick-and-place procedure is executed using a robotic arm (Trossen Robotics, Viper X 250). The DYNAMIXEL servomotors of the robotic arm are programmed using Python software supported by the Robotic Operating System. Beyond its technical construction, this system is uniquely fashioned for academic research, providing invaluable hands-on experience in gamma spectrometry to both junior researchers and students.

Identification and Suppression of Point Defects in Bromide Perovskite Single Crystals Enabling Gamma-Ray Spectroscopy.

Methylammonium lead tribromide (MAPbBr3) stands out as the most easily grown wide-band-gap metal halide perovskite. It is a promising semiconductor for room-temperature gamma-ray (γ-ray) spectroscopic detectors, but no operational devices are realized. This can be largely attributed to a lack of understanding of point defects and their influence on detector performance. Here, through a combination of crystal growth design and defect characterization, including positron annihilation and impedance spectroscopy, the presence of specific point defects are identified and correlated to detector performance. Methylammonium (MA) vacancies, MA interstitials, and Pb vacancies are identified as the dominant charge-trapping defects in MAPbBr3 crystals, while Br vacancies caused doping. The addition of excess MABr reduces the MA and Br defects and so enables the detection of energy-resolved γ-ray spectra using a MAPbBr3 single-crystal device. Interestingly, the addition of formamidinium (FA) cations, which converted to methylformamidinium (MFA) cations by reaction with MA+ during crystal growth further reduced MA defects. This enabled an energy resolution of 3.9% for the 662 keV 137Cs line using a low bias of 100 V. The work provides direction toward enabling further improvements in wide-bandgap perovskite-based device performance by reducing detrimental defects.

A new generation of scintillation detectors with identification of events undergoing multiple interactions for gamma-ray imaging and spectroscopy.

The present work deals with a scintillation detector made of a LuYAP:Ce array coupled to a position-sensitive photo-multiplier tube, whose structure is well suitable for SPECT and PET, but also in nuclear physics, astrophysics, astroparticle physics, homeland security, and non-proliferation. The response was investigated under Co-57, Ba-133, Cs-137 gamma-ray irradiation, and with Lu-176 self-activity. The investigation, based on the 2-D charge-profiles spread, provides means for identifying and rejecting multiple-interactions in the crystal-array, like Lu X-ray escape photons, and Compton-scattered ones.

In-silico optimisation of tileable philips digital SiPM based thin monolithic scintillator detectors for SPECT applications.

Over the last decade one of the most significant technological advances made in the field of radiation detectors for nuclear medicine was the development of Silicon Photomultipler (SiPM) sensors. At present only a small number of SiPM based radiation detectors for Single Photon Emission Computed Tomography (SPECT) applications have been explored, and even fewer experimental prototypes developed. An in-silico investigation into the optimal design of a Philips DPC3200 SiPM photosensor-based thin monolithic scintillator detector for SPECT applications was undertaken using the Monte Carlo radiation transport modelling toolkit Geant4 version 10.5. The performance of the 20 different SPECT radiation detector configurations, 4 scintillator materials (NaI(Tl), GAGG(Ce), CsI(Tl) and LaBr3(Ce)) and 5 thicknesses (1-5 mm), were determined through the use of seven figures of merit. It was found that a crystal thickness range of 4-5 mm was required for all four materials to ensure acceptable energy resolution, sensitivity and spatial resolution performance with the Philips DPC3200 SiPM. Any thinner than this and the performance of all four materials was found to degrade rapidly due to a high probability of material specific fluorescence x-ray escape after incident gamma/x-ray photoelectric absorption. When factoring in each material's magnetic resonance imaging compatibility, hygroscopy, and cost, it was found that CsI(Tl) represents the most promising material to construct tileable Philips digital SiPM based thin monolithic scintillator detectors for SPECT applications.

Directional probe for radio-guided surgery: A pilot study.

PURPOSE: The sentinel lymph node (SLN) biopsy technique has highly evolved during the last 20 yr. Consequently, the intraoperative use of Gamma Probes (GPs) for SLN mapping is increased. This preliminary study evaluates a novel directional GP prototype. This proof-of-concept prototype is designed to identify the direction of radiopharmaceuticals uptakes, by combining the information from multiple detectors. The purpose of this work is to develop a tool able to effectively guide the surgeon reducing the surgery time. METHODS: The proposed prototype consists of three CsI(Tl) scintillation crystals, each coupled with an S10931 silicon photomultiplier (Hamamatsu Photonics K.K., Hamamatsu, JP). The three detectors lie on the same plane with an angle of 30° between them. The central detector is placed as in a common GP, so it can be used to pinpoint the target tissue. Meanwhile, the lateral sensors provide a broader view of the surgical field. A dedicated data acquisition system digitizes and processes the signals from the front-end electronics. Finally, an embedded system, based on ARM processor, calculates and displays the acquired count rates. In order to assess the prototype behavior, the isosensitivity curves for the three detectors were measured. Meanwhile, for the central one, the main quality criteria measurements were also performed (i.e., sensitivity, radial sensitivity, and spatial resolution). RESULTS: For the central detector, the measured sensitivity at the tip of the probe is better than 5 cps/kBq. The full width at half maximum (FWHM) of the radial sensitivity is less than 30° and the FWHM of the lateral sensitivity (spatial resolution) is about 7.2 mm. The central detector measured isosensitivity distribution shows a narrow profile in agreement with the spatial resolution measured. On the contrary, the two lateral detectors exhibit widespread isosensitivity distributions that mean a larger field of view. The system had shown satisfactory performance and reliability, meeting the minimal requirements of gamma probe systems. CONCLUSIONS: The prototype presented in this paper allows a rapid localization by the use of the whole system, while the sole central detector can be used to pinpoint the target source. This device, unlike common GPs, allows localizing simultaneously different areas of radiopharmaceuticals uptake, thus precisely guiding the surgeon to the region of interest. These preliminary results encourage to develop a further prototype for intraoperative validation.

Spatial pattern of atmospherically deposited radiocesium on the forest floor in the early phase of the Fukushima Daiichi Nuclear Power Plant accident.

Spatial patterns of atmospherically deposited radiocesium on the forest floor and the temporal evolution were measured in two Japanese cedar stands and a secondary mixed broad-leaved forest in the early phase of the Fukushima Daiichi Nuclear Power Plant accident. In situ measurements of the 137Cs gamma count were made using a portable germanium gamma ray detector. These measurements revealed that the forest floors were contaminated with radionuclides derived from the accident. In the cedar stands, the inter-canopy area had higher 137Cs count rate relative to the under-canopy area, whereas no clear relationship was found between the radiocesium pattern and canopy cover in the mixed broad-leaved forest. Repeated radiocesium measurements revealed that the spatial pattern of radiocesium activity on the forest floor did not substantially change following additional deposition inputs. Furthermore, the magnitude of canopy cover partially explained spatial variability of the 137Cs on the forest floor in cedar stands. These results suggest that canopy structure affected the genesis of the horizontal variability of atmospherically deposited radiocesium on the forest floor during the early phase of the Fukushima accident.

Design and study of a coplanar grid array CdZnTe detector for improved spatial resolution.

Coplanar grid (CPG) CdZnTe detectors have been used as gamma-ray spectrometers for years. Comparing with pixelated CdZnTe detectors, CPG CdZnTe detectors have either no or poor spatial resolution, which directly limits its use in imaging applications. To address the issue, a 2×2 CPG array CdZnTe detector with dimensions of 7×7×5mm(3) was fabricated. Each of the CPG pairs in the detector was moderately shrunk in size and precisely designed to improve the spatial resolution while maintaining good energy resolution, considering the charge loss at the surface between the strips of each CPG pairs. Preliminary measurements were demonstrated at an energy resolution of 2.7-3.9% for the four CPG pairs using 662keV gamma rays and with a spatial resolution of 3.3mm, which is the best spatial resolution ever achieved for CPG CdZnTe detectors. The results reveal that the CPG CdZnTe detector can also be applied to imaging applications at a substantially higher spatial resolution.