X-ray and gamma-ray imaging are technologies with several applications in nuclear medicine, homeland security, and high-energy astrophysics. However, it is generally difficult to realize simultaneous wide-band imaging ranging from a few tens of keV to MeV because different interactions between photons and the detector material occur, depending on the photon energies. For instance, photoabsorption occurs below 100 keV, whereas Compton scattering dominates above a few hundreds of keV. Moreover, radioactive sources generally emit
both
X-ray and gamma-ray photons. In this study, we develop a “hybrid” Compton camera that can simultaneously achieve X-ray and gamma-ray imaging by combining features of “Compton” and “pinhole” cameras in a single detector system. Similar to conventional Compton cameras, the detector consists of two layers of scintillator arrays with the forward layer acting as a scatterer for high-energy photons (> 200 keV) and an active pinhole for low-energy photons (< 200 keV). The experimental results on the performance of the hybrid camera were consistent with those from the Geant4 simulation. We simultaneously imaged
Am (60 keV) and
Cs (662 keV) in the same field of view, achieving an angular resolution of 10
(FWHM) for both sources. In addition, imaging of
At was conducted for the application in future nuclear medicine, particularly radionuclide therapy. The initial demonstrative images of the
At phantom were reconstructed using the pinhole mode (using 79 keV) and Compton mode (using 570 keV), exhibiting significant similarities in source-position localization. We also verified that a mouse injected with 1 MBq of
At can be imaged via pinhole-mode measurement in an hour.
Gamma‐ray glows associated with thunderclouds have been observed since the 1980s, however it remains unclear how, and at which thunderstorms gamma‐ray glows are generated in dense atmospheres. In this study, we report the first Compton camera imaging of a gamma‐ray glow from a winter thundercloud. On 14 January 2022, using two identical Bi4Ge3O12 scintillators in energy range of 0.05–5 MeV, we detected two gamma‐ray glows lasting ∼4 min in a mountain area 25 km from the Japan Sea and 410 m above sea level. The same events were also observed by the Compton camera, where the first glow we observed suggested statistically significant (4.0 and 5.9 σ level) signals of two enhanced concentrations in gamma‐ray photon images in a range of 0.15–1.5 MeV. These concentrations were most clearly observed in a time window of Δt = 50 s around the peak intensity of the gamma‐ray glow.
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