Recent technological innovations are finding their way into biomedical imaging systems just in time to impact emerging therapeutic innovations for some of the most challenging human health problems, such as cancer and neurodegenerative diseases. Imaging with high-energy photons and alpha/beta particles is especially useful in supporting research and personalized medicine in the rapidly developing field of targeted radiotherapy, where it is important to understand the details of dose delivery. In this context, we will consider the significance of novel geometries for direct- and indirect-conversion detectors and cameras, new architectures for data acquisition systems, new fabrication methods, and new computing platforms for physics modeling and image reconstruction.

Perovskite-based radiation detectors have attracted increasing attention in a broad range of fields, such as homeland security, medical diagnosis, and industrial inspection, due to their excellent physical properties including high attenuation coefficients, attractive charge transport properties, tunable bandgap, and most importantly, cost-effective manufacturing. However, to increase the stopping power to high energy radiation, most of the previously studied perovskite radiation detector materials contain lead (Pb), which is toxic and poses health concerns to both human-beings and the environment. As such, there is a strong need to develop lead-free perovskite materials for radiation detection. Here, we report our efforts to develop lead-free perovskite, FA3Bi2I9, single crystals for X-ray detection and imaging applications. A series of annealing experiments were conducted to improve the properties of FA3Bi2I9 crystals for radiation detection. Systematic microstructural-, electrical-, optical-, and mechanical- characterization results, together with X-ray response testing, will be presented and discussed.

Inorganic double perovskite single crystals e.g. Cs2AgBiBr6 have great potential in detecting X- and Gamma-Radiation. These single crystals can be solution processed at low temperature and be possessing of low trap density, high charge carrier mobility, and a tunable bandgap. In this work, Cs2AgBiBr6 single crystals were synthesized using the solution growth method, and we tried to determine the potential of detecting X-Ray radiation by examining especially their electrical and optical properties. Besides that, the values determined by the IV measurement along the dominant {001} lattice plane (1.02x108 – 2.97x109 Ωcm) and the van der Paul measurements made along the trigonal upper surface and pseudo-hexagonal lower surface edges (2.88X109 – 4.39x1010 Ωcm) used for specifically demonstrate the correlation between structure and property. The density of trap states and charge-carrier mobilities, which were calculated from the IV characteristic curve measurements, are 4.44x109 – 6.79x1010 cm–3 and 0.07-24.4 cm2V–1s–1, respectively. Consequently, it has been seen that these crystals obtained by the solution growth method are suitable for use in radiation sensors applications.

Quaternary compound semiconductor Cd0.9Zn0.1Te1-xSex (CZTS) is emerging as the next generation room-temperature detector for radiation spectroscopy and imaging. CZTS is grown by inclusion of Se in small amount (2-3 at. %) in the CdZnTe (CZT) matrix during the crystal growth. Travelling heater method (THM) and Bridgman method (BM) grown CZTS ingots have shown high degree of axial and radial compositional homogeneity leading to crystal growth yield higher than 90% unforeseen in CZT. While the conventional growth methods produce large volume detector grade crystals, the achievable growth rate is typically low – 1-2 mm/day for THM and 1-2 mm/hr for BM. Vertical gradient freeze (VGF) method is an alternative growth method that can deliver much higher growth rates while maintaining the electronic quality of the crystals. We report an electron drift mobility of 1245 cm^2/V/s, measured in a VGF-grown Cd0.9Zn0.1Te0.97Se0.03 (CZTS) single crystal using a time-of-flight alpha spectroscopic method, which is 1.5 times higher than that reported for state-of-the-art CZTS crystals. A mobility-lifetime (μτ) product of ~1x10^-3 cm^2/V was calculated using a single polarity Hecht plot. Photo-induced deep level transient spectroscopy (PICTS) revealed the presence of several charge trapping centers in the temperature scan range 80 - 450 K. The study correlates the effect of the trap parameters on the performance of room-temperature gamma-ray detectors grown using the VGF method.

Additive manufacturing techniques are being extended to refractory metals and other metals capable of operating in high-temperature environments. Many of these metals are high-Z and high density necessitating higher x-ray inspection energies. 3D volumetric X-ray computed tomography (X-ray CT) has emerged as a strategic inspection choice for these parts. The internal channels and features of these parts are often complicated and can articulate in spiral configurations for longer chord lengths that are difficult to inspect in a single or ensemble of radiographs. In particular, it is the entire 3D structure of the part that is of interest not just one or two locations in the volume. At the same time, 3D printing is extending the spatial resolution limits for small, manufactured details and defects, which impacts the target resolution. CT inspection requirements for these parts include resolution down to 0.1 mm at MeV energies. In this context, properties of the GLO transparent ceramic scintillator (Gd0.3Lu1.6Eu0.1O3): high-stopping power, high-brightness, high transparency in large area plates combined to produce high intrinsic spatial resolution, could be pivotal for delivering 3D inspections of these parts. Radiabeam LLC has configured an area-detector CT camera-scintillator system employing GLO (other scintillators have been used in this system) in combination with the ARCIS LINAC (adjustable from 2-9 MeV). A variety of AM-fabricated refractory metal components have been scanned at 7.8 MeV, providing robust transmitted signal for high density parts with 2-3” chord lengths, in parts that are up to 6 inches in diameter. Lens-coupled X-ray CT using a transparent scintillator imaged on a sCMOS camera obtains higher spatial resolution than the more commonly employed phosphor-enhanced amorphous silicon (A-Si) panels. The result is higher contrast imaging due to increased stopping power. Interior features of the additively manufactured components have been resolved down to a voxel size of 80 microns. Inspection data from this system with representative AM parts will be reviewed and evaluated.

The improvements of the accuracy of mixture synthesis in X-ray imaging using noise correction per pixel was aimed in this study. Direct conversion type detectors with semiconductors were used, and image correction was performed for each pixel. The entire image was synthesized in each energy band, and the results were compared to the image as energy integrated type. The imaging corrected using shot noise showed better contrast for both low and high atomic number areas, synthesizing multiple mixtures in a single image data without compromising contrast. This result could lead to higher accuracy in X-ray imaging for detecting mixed materials.

We have reported on the growth of single-crystal diamond and its application to radiation detectors. This time, we report on the measurement of an imager with a photon-charge counting read out integrated circuit (ROIC) connected to a single-crystal diamond. The single crystal diamond was 3.0 x 3.0mm x 0.5mm thick. The bump connection area of our test ROIC is a 3.2mm x 3.2mm area with 40 x 40 pixels pads with 80µm pitch. Silver-based bumps were formed on short-crystal diamond using a super inkjet printer and bumped to the ROIC using flip chip bonders. The imaging experiment was conducted by irradiating X-rays at 90 kV and 0.2 mA at 30cm distance. The results showed that the X-ray transmission image with a clear contrast between the area shielded by 2 mm thick lead and the unshielded area was captured, demonstrating a prototype single-crystal diamond-type X-ray imager.

Spectroscopic detection of gamma photons has widespread applications for particle physics research, threat detection and medical diagnosis. We report the development of plastic scintillators for gamma photoelectric generation. High-Z nanoparticles are loaded at high concentrations to enhance the gamma cross-section, and conjugated organic luminescent compounds are investigated to boost the light yield. Factors affecting the synthesis, optical transparency, light yield and radiation hardness will be discussed.

Plastic scintillators incorporating up to 8 weight percent element bismuth are being developed as drop-in replacements for current portal monitor plastics. They use the same fluors with fast decay times (<10 ns) while offering enhanced sensitivity with more than 8x increased counts from Am-241 for the same detector volume. In this work, we report on the largest samples produced to date with volumes over 135 in3, and compare their performance to currently fielded plastic scintillators.

Recent research in manufacturing plastic scintillators via photopolymerization has reported various non-aromatic acrylic-based resins for easy 3D printing. However, the absence of traditionally used aromatic matrices, such as polystyrene or poly(vinyl toluene) (PVT), resulted in a limited scintillation performance. In this research, the feasibility of accommodating a high ratio of PVT with pentaerythritol tetraacrylate was demonstrated by the synthesis of plastic scintillators with efficient pulse shape discrimination. Moreover, the research described the understanding of the current inferior performance of photocured plastics compared to thermally cured analogs and showed 3D printability of studied resins in different shapes.