Articoli di riviste: "Gamma-rays imaging"

1

Zarifmahmoudi, Leili, e Ramin Sadeghi. "Scattered gamma rays". Nuclear Medicine Communications 36, n. 7 (luglio 2015): 755–56. http://dx.doi.org/10.1097/mnm.0000000000000324.

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Koshikawa, N., A. Omata, M. Masubuchi, Y. Okazaki, J. Kataoka, K. Matsunaga, H. Kato, A. Toyoshima, Y. Wakabayashi e T. Kobayashi. "Activation imaging of drugs with hybrid Compton camera: A proof-of-concept study". Applied Physics Letters 121, n. 19 (7 novembre 2022): 193701. http://dx.doi.org/10.1063/5.0116570.

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The visualization of drugs is essential for cancer treatment. Although several methods for visualizing drugs have been proposed, a versatile method that can be easily applied to various drugs has not yet been established. Therefore, we propose “activation imaging,” in which a drug is irradiated with thermal neutrons and becomes radioactive, enabling visualization using emitted x rays and/or gamma rays. Activation imaging does not require the conjugation of specific tracers with drugs. Therefore, it can be easily applied to a variety of drugs, drug carriers (e.g., metal nanoparticles), and contrast agents. In this study, neutron activation, gamma-ray spectroscopy, and imaging of drug carriers, anticancer drug, and contrast agents were performed. Gold nanoparticles (AuNPs) and platinum nanoparticles were used as drug carriers, cisplatin was used as an anticancer drug, and gadoteridol and iohexol were used as contrast agents. As a neutron source, the RIKEN accelerator-driven compact neutron source II (RANS-II) was utilized. The imaging was performed using a hybrid Compton camera (HCC). The HCC can visualize x rays and gamma rays ranging from a few keV to nearly 1 MeV, which enables the imaging of various x rays and gamma rays emitted from the activated drugs. As a result, the gamma-ray spectra indicated the generation of radioisotopes through neutron irradiation, and AuNPs and iohexol were visualized.

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Uenomachi, M., K. Shimazoe e H. Takahashi. "Double photon coincidence crosstalk reduction method for multi-nuclide Compton imaging". Journal of Instrumentation 17, n. 04 (1 aprile 2022): P04001. http://dx.doi.org/10.1088/1748-0221/17/04/p04001.

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Abstract Compton imaging based on Compton scattering kinematics has the potential to visualize multi-nuclides by discriminating the total energy of Compton scattering and photoelectric absorption events. This feature enables us to perform multi-tracer imaging that reflects different functional information in nuclear medicine, resulting in a definitive diagnosis and being useful for biological and medical research. One of the challenges with multi-nuclide imaging is the crosstalk artifacts caused by scattered photons of higher energy gamma-rays. In this study, we investigated the potential benefits of the double photon coincidence detection as a drastic crosstalk reduction method. Coincidence detection of successive gamma-rays can differentiate nuclides and reduce the background caused by other nuclides' gamma-rays because some nuclides emit two or more gamma-rays in rapid succession. In this study, we focused on the coincidence detection of a Compton event and a photoelectric absorption event, and we showed simultaneous double photon emitter imaging of 111In and 177Lu with a ring-type Compton imaging system. The artifacts caused by other nuclides' gamma-rays were reduced by extracting Compton events coincident with photoelectric absorption events. The coincidence Compton images demonstrated a signal-to-background ratio improvement of 1.1–1.7 times over the one of no-coincidence Compton images, despite a drop in intrinsic detection efficiency of the order of 10-2. This strategy of directly reducing crosstalk will be useful in other combinations imaging such as of 111In (or 177Lu) and a positron emission tomography nuclide.

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Yamamoto, Seiichi, Hiroshi Watabe, Kohei Nakanishi, Takuya Yabe, Mitsutaka Yamaguchi, Naoki Kawachi, Kei Kamada et al. "A triple-imaging-modality system for simultaneous measurements of prompt gamma photons, prompt x-rays, and induced positrons during proton beam irradiation". Physics in Medicine & Biology 69, n. 5 (22 febbraio 2024): 055012. http://dx.doi.org/10.1088/1361-6560/ad25c6.

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Abstract Objective. Prompt gamma photon, prompt x-ray, and induced positron imaging are possible methods for observing a proton beam’s shape from outside the subject. However, since these three types of images have not been measured simultaneously nor compared using the same subject, their advantages and disadvantages remain unknown for imaging beam shapes in therapy. To clarify these points, we developed a triple-imaging-modality system to simultaneously measure prompt gamma photons, prompt x-rays, and induced positrons during proton beam irradiation to a phantom. Approach. The developed triple-imaging-modality system consists of a gamma camera, an x-ray camera, and a dual-head positron emission tomography (PET) system. During 80 MeV proton beam irradiation to a polymethyl methacrylate (PMMA) phantom, imaging of prompt gamma photons was conducted by the developed gamma camera from one side of the phantom. Imaging of prompt x-rays was conducted by the developed x-ray camera from the other side. Induced positrons were measured by the developed dual-head PET system set on the upper and lower sides of the phantom. Main results. With the proposed triple-imaging-modality system, we could simultaneously image the prompt gamma photons and prompt x-rays during proton beam irradiation. Induced positron distributions could be measured after the irradiation by the PET system and the gamma camera. Among these imaging modalities, image quality was the best for the induced positrons measured by PET. The estimated ranges were actually similar to those imaged with prompt gamma photons, prompt x-rays and induced positrons measured by PET. Significance. The developed triple-imaging-modality system made possible to simultaneously measure the three different beam images. The system will contribute to increasing the data available for imaging in therapy and will contribute to better estimating the shapes or ranges of proton beam.

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Tian, B. B., B. Jiang, H. T. Jing e M. F. Yan. "Monte Carlo simulation study of a novel neutron resonance radiography method for oxygen identification in oxides and composite materials". Journal of Instrumentation 19, n. 09 (1 settembre 2024): T09002. http://dx.doi.org/10.1088/1748-0221/19/09/t09002.

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Abstract A novel imaging mode of neutron resonance radiography for the identification and mapping of oxygen element is firstly proposed based on the Back-n beamline at CSNS. The method utilizes a 10B-enriched conversion layer that converts transmitted neutrons to gamma rays. The emitted characteristic 478-keV prompt gamma rays are then collimated by a pinhole device and imaged. The energy-selective operation of transmitted neutrons via time-of-flight (TOF) measurement is performed by detecting 478-keV prompt gamma rays as a function of neutron TOF. This work shows the viability of the proposed imaging method for oxygen identification by Monte Carlo simulation.

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Uenomachi, Mizuki, Kenji Shimazoe e Hiroyuki Takahashi. "A double photon coincidence detection method for medical gamma-ray imaging". Bio-Algorithms and Med-Systems 18, n. 1 (1 dicembre 2022): 120–26. http://dx.doi.org/10.2478/bioal-2022-0080.

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Abstract Cascade nuclides emit two or more gamma rays successively through an intermediate state. The coincidence detection of cascade gamma rays provides several advantages in gamma-ray imaging. In this review article, three applications of the double photon coincidence method are reviewed. Double-photon emission imaging with mechanical collimators and Compton double-photon emission imaging can identify radioactive source positions with their angular-resolving detectors, and reduce the crosstalk between nuclides. In addition, a novel method of coincidence Compton imaging is proposed by taking coincidence detection between a Compton event and a photopeak events. Although this type of coincidence Compton imaging cannot specify the location, it can be useful in multi-nuclide Compton imaging.

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van der Marel, J., e B. Cederwall. "Collimatorless imaging of gamma rays with help of gamma-ray tracking". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 471, n. 1-2 (settembre 2001): 276–80. http://dx.doi.org/10.1016/s0168-9002(01)01007-5.

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8

Sun, Y. K., H. T. Jing, B. B. Tian, X. L. Gao e X. Y. Yang. "Research on proton beam spot imaging based on pixelated gamma detector". Journal of Instrumentation 17, n. 02 (1 febbraio 2022): P02033. http://dx.doi.org/10.1088/1748-0221/17/02/p02033.

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Abstract The secondary particles from the spallation target of the China Spallation Neutron Source are mainly gammas and neutrons, which are related to the incident proton. The reconstruction of the proton beam spot could be implemented based on the distribution of the positions of secondary gammas or neutrons. The methods of pinhole imaging and Compton imaging are developed by measuring the position distribution of gammas based on the pixelated detector. The secondary gammas could be detected by the pixelated gamma detector directly. The neutron can be identified by detecting the characteristic (478 keV) γ-rays from the 10B(n, α) reactions. In order to detect secondary neutrons, a layer of 10B converter is added before the pixelated gamma detector. The pixelated gamma detector is sensitive to the characteristic (478 keV) γ-rays and then the neutron imaging could be achieved based on measuring the position distribution of the characteristic (478 keV) γ-rays.

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Yamamoto, Seiichi, Tomohiro Yamashita, Yusuke Kobashi, Takuya Yabe, Takashi Akagi, Mitsutaka Yamaguchi, Naoki Kawachi et al. "Simultaneous imaging of prompt gamma photons and prompt X-rays during irradiation of proton beams to human torso phantom at clinical dose level". Journal of Instrumentation 18, n. 07 (1 luglio 2023): P07046. http://dx.doi.org/10.1088/1748-0221/18/07/p07046.

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Abstract Although both prompt gamma photon and prompt X-ray imaging are promising methods for observing a beam shape and estimating the range of the beam from outside a subject, the images using these two methods have not been compared under realistic conditions such as in a human torso phantom. To clarify the imaging capability of prompt gamma photon and prompt X-ray imaging, simultaneous imaging with these methods was conducted during irradiation by proton beams to a human torso phantom at clinical dose level. After a human torso phantom was set on the bed of a proton therapy system, proton pencil beams of three different energies at clinical dose level and a patient planning beam for prostate cancer were used to irradiate the phantom. Prompt gamma photons and prompt X-rays emitted from the phantom were simultaneously imaged by a developed gamma camera and an X-ray camera during irradiation with proton beams to the human torso phantom. For all of the tested beams, we could obtain the beam shapes of prompt gamma photons and prompt X-rays images. The ranges could be estimated within a difference of 11 mm and 14 mm from the calculated dose for prompt gamma photon and prompt X-ray images, respectively. For both types of images, time sequential images and time count rate curves could be derived. We could clarify the imaging capabilities of prompt gamma photons and prompt X-rays were different by the simultaneous imaging during proton irradiation to a human torso phantom. Although both methods had advantages and disadvantages, we confirmed that both methods are promising for beam imaging in a torso phantom and also for future clinical use in proton therapy.

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Li, Y., P. Gong, X. Tang, Z. Hu, P. Wang, F. Tian, S. Wu, M. Ye, C. Zhou e X. Zhu. "DOI correction for gamma ray energy reconstruction based on energy segment in 3D position-sensitive CdZnTe detectors". Journal of Instrumentation 17, n. 03 (1 marzo 2022): T03004. http://dx.doi.org/10.1088/1748-0221/17/03/t03004.

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Abstract The amplitude of the induced signal in 3D CdZnTe detector depends on the depth of interaction (DOI). Therefore, calibrating the detector by using DOI correction technology plays a crucial role in improving the energy resolution of the detectors to gamma rays. The current DOI correction method focuses on the single energy gamma rays, and its application to multiple energy gamma-rays are not found. In this study, we propose an improved energy correction algorithm with excellent correction results in the multiple energy gamma-ray detection. In the experiment, the DOI correction factors of a CdZnTe detector under different energies are discussed. The energy resolution and peak height of multiple energy peaks in the energy spectrum are significantly improved by using the segment energy correction method. We also extend the DOI correction method to the gamma detectors used in the Compton imaging, and the influence of this method on the Compton imaging quality is also discussed. For a single 60Co point source, the intrinsic efficiency increases from 6.5‰ to 8.3‰.

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Aprile, E., A. Curioni, K. L. Giboni, M. Kobayashi, U. G. Oberlack e S. Zhang. "Compton imaging of MeV gamma-rays with the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 593, n. 3 (agosto 2008): 414–25. http://dx.doi.org/10.1016/j.nima.2008.05.039.

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Das, Biswajit, R. Palit, R. Donthi, A. Kundu, S. R. Laskar, P. Dey, D. Negi et al. "Development of a position-sensitive fast scintillator (LaBr₃(Ce)) detector setup for gamma-ray imaging application". EPJ Web of Conferences 253 (2021): 11005. http://dx.doi.org/10.1051/epjconf/202125311005.

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We have characterized a Cerium doped Lanthanum Bromide (LaBr3(Ce) ) crystal coupled with the position-sensitive photo-multiplier system for the gamma-ray imaging application. One can use this detector set-up for the scanning of high purity germanium detectors for pulse shape analysis in gamma-ray spectroscopy experiments and the image formation of an object by Compton back-scattering . The sensor has been tested for energy, timing and position information of the gamma-rays interacting within the detector crystal. The GEANT4 simulation results are consistent with the experimental results. We have reconstructed the image of irradiation spots in different positions throughout the detector crystal. Position resolution is found to be around 3.5 mm with the 2 mm collimated gamma-rays. The 2-d image of hexagonal Bismuth Germanate (BGO) crystal and a cylindrical LaBr3(Ce) crystal have been reconstructed in coincidence technique. The performance of the detector for imaging application has been investigated by coincidence technique in GEANT4 simulation and compared with the experimental data. We have reconstructed the 2-d images of objects with various geometrical shapes by Compton back-scattered events of the gamma-rays. This position-sensitive detector can be used as an absorber of a Compton camera for the image reconstruction of an extended radioactive source. One can also use this kind of set-up as in radiation imaging and many other applications where the energy and source position of the gamma-ray is the main interest.

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Looker, Q., L. C. Stonehill, M. S. Wallace, M. Galassi, M. M. Cowee, E. Fenimore e W. Vogan McNeil. "Demonstration of imaging via backscattering of annihilation gamma rays". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 615, n. 3 (aprile 2010): 295–300. http://dx.doi.org/10.1016/j.nima.2010.01.078.

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Monkhoev, R., M. Ternovoy, I. Astapov, P. Bezyazeekov, A. Borodin, M. Brueckner, N. Budnev et al. "Geant4 simulation of the Tunka-Grande experiment". Journal of Physics: Conference Series 2103, n. 1 (1 novembre 2021): 012001. http://dx.doi.org/10.1088/1742-6596/2103/1/012001.

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Abstract The Tunka-Grande array is part of a single experimental complex, which also includes the Tunka-133 and TAIGA-HiScORE (High Sensitivity COsmic Rays and gamma Explorer) wide-angle Cherenkov arrays, TAIGA-IACT array (Imaging Atmospheric Cherenkov Telescope) and TAGA-MUON scintillation array. This complex is located in the Tunka Valley (Buryatia Republic, Russia), 50 km from Lake Baikal. It is designed to study the energy spectrum and the mass composition of charged cosmic rays in the energy range 100 TeV - 1000 PeV, to search for diffuse gamma rays above 100 TeV and to study local sources of gamma rays with energies above 30 TeV. This report outlines 3 key points. The first is the description of the Tunka-Grande scintillation array. The second one presents the computer simulation strategy of the Tunka Grande array based on the Geant4 software. The third one is devoted to the prospects for future research in the field of cosmic ray physics and gamma-ray astronomy using simulation results.

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Sagisaka, Yuri, Yasuyuki Takahashi, Shota Hosokawa, Niina Kanazawa, Hiroki Yamamoto, Go Takai e Keiji Nagano. "Acquisition Conditions for Lu-177 DOTATATE Imaging". Radiation 4, n. 1 (19 gennaio 2024): 17–25. http://dx.doi.org/10.3390/radiation4010002.

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We investigated imaging conditions for the distribution of lutetium oxodotreotide (Lu-177 DOTATATE) in the body during peptide receptor radionuclide therapy for neuroendocrine tumor (NET). We investigated imaging conditions using gamma rays emitted from the radionuclide. The gamma rays had energy peaks at 113 and 208 keV and characteristic X-rays at 56 keV. Image quality was compared by utilizing a combination of low–medium-energy general-purpose (LMEGP) and medium-energy general-purpose (MEGP) collimators. This study included the measurement of total spatial resolution (Full Width at Half Maximum) using a line source phantom. We compared the image quality of static images using a plane phantom and SPECT images using a cylindrical phantom. This comparison involved assessing recovery coefficient curves, count ratio, and %CV. Imaging evaluation was also performed on one NET patient. In phantom studies and the clinical study, comparing the combination of the three energy peaks (56 + 113 + 208 keV) using the LMEGP collimator and the conventional combination (113 + 208 keV) using the MEGP collimator revealed a count ratio of 1.9 times the maximum, stable %CV, and the best image quality.

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Buuck, M., A. Mishra, E. Charles, N. Di Lalla, O. A. Hitchcock, M. E. Monzani, N. Omodei e T. Shutt. "Low-energy Electron-track Imaging for a Liquid Argon Time-projection-chamber Telescope Concept Using Probabilistic Deep Learning". Astrophysical Journal 942, n. 2 (1 gennaio 2023): 77. http://dx.doi.org/10.3847/1538-4357/aca329.

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Abstract The GammaTPC is an MeV-scale single-phase liquid argon time-projection-chamber gamma-ray telescope concept with a novel dual-scale pixel-based charge-readout system. It promises to enable a significant improvement in sensitivity to MeV-scale gamma rays over previous telescopes. The novel pixel-based charge readout allows for imaging of the tracks of electrons scattered by Compton interactions of incident gamma rays. The two primary contributors to the accuracy of a Compton telescope in reconstructing an incident gamma-ray’s original direction are its energy and position resolution. In this work, we focus on using deep learning to optimize the reconstruction of the initial position and direction of electrons scattered in Compton interactions, including using probabilistic models to estimate predictive uncertainty. We show that the deep-learning models are able to predict locations of Compton scatters of MeV-scale gamma rays from simulated 500 μm pixel-based data to better than 1 mm rms error and are sensitive to the initial direction of the scattered electron. We compare and contrast different deep-learning uncertainty estimation algorithms for reconstruction applications. Additionally, we show that event-by-event estimates of the uncertainty of the locations of the Compton scatters can be used to select those events that were reconstructed most accurately, leading to improvement in locating the origin of gamma-ray sources on the sky.

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Takada, Atsushi, Taito Takemura, Kei Yoshikawa, Yoshitaka Mizumura, Tomonori Ikeda, Yuta Nakamura, Ken Onozaka et al. "First Observation of the MeV Gamma-Ray Universe with Bijective Imaging Spectroscopy Using the Electron-tracking Compton Telescope on Board SMILE-2+". Astrophysical Journal 930, n. 1 (28 aprile 2022): 6. http://dx.doi.org/10.3847/1538-4357/ac6103.

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Abstract MeV gamma-rays provide a unique window for the direct measurement of line emissions from radioisotopes, but observations have made little significant progress since COMPTEL on board the Compton Gamma-ray Observatory (CGRO). To observe celestial objects in this band, we are developing an electron-tracking Compton camera (ETCC) that realizes both bijective imaging spectroscopy and efficient background reduction gleaned from the recoil-electron track information. The energy spectrum of the observation target can then be obtained by a simple ON–OFF method using a correctly defined point-spread function on the celestial sphere. The performance of celestial object observations was validated on the second balloon SMILE-2+ , on which an ETCC with a gaseous electron tracker was installed that had a volume of 30 × 30 × 30 cm3. Gamma-rays from the Crab Nebula were detected with a significance of 4.0σ in the energy range 0.15–2.1 MeV with a live time of 5.1 hr, as expected before launch. Additionally, the light curve clarified an enhancement of gamma-ray events generated in the Galactic center region, indicating that a significant proportion of the final remaining events are cosmic gamma-rays. Independently, the observed intensity and time variation were consistent with the prelaunch estimates except in the Galactic center region. The estimates were based on the total background of extragalactic diffuse, atmospheric, and instrumental gamma-rays after accounting for the variations in the atmospheric depth and rigidity during the level flight. The Crab results and light curve strongly support our understanding of both the detection sensitivity and the background in real observations. This work promises significant advances in MeV gamma-ray astronomy.

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Haga, Y. Karasawa, S. Kumazawa e N. Niimura. "Gamma-ray sensitivity and shielding of a neutron imaging plate". Journal of Applied Crystallography 32, n. 5 (1 ottobre 1999): 878–82. http://dx.doi.org/10.1107/s0021889899005701.

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The energy dependence of gamma-ray sensitivity of a neutron imaging plate (NIP) has been measured. The gamma-ray sensitivity is equivalent to one half that of a thermal neutron at a gamma-ray energy less than 300 keV, and 1/40 at greater than 300 keV. The shielding of the NIP, by lead, from gamma rays in the experimental hall of the reactor JRR-3M of the Japan Atomic Energy Research Institute (JAERI) was measured. It was found that lead of thickness 40 mm is sufficient to reduce the gamma-ray background to 1/10 on a normalized scale. Covering the NIP with lead foil of thickness 1 mm results in a decrease of the gamma-ray background without reduction of the neutron signal.

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Sol, Helene. "Very High Energy gamma-rays from blazars". Proceedings of the International Astronomical Union 9, S304 (ottobre 2013): 119–24. http://dx.doi.org/10.1017/s1743921314003524.

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AbstractThe extragalactic very high energy (VHE) gamma-ray sky is dominated at the moment by more than fifty blazars detected by the present imaging atmospheric Cherenkov telescopes (IACT), with a majority (about 90%) of high-frequency peaked BL Lac objects (HBL) and a small number of low-frequency peaked and intermediate BL Lac objects (LBL and IBL) and flat spectrum radio quasars (FSRQ). A significant variability is often observed, with time scales from a few minutes to months and years. The spectral energy distribution (SED) of these blazars typically shows two bumps from the radio to the TeV range, which can usually be described by leptonic or hadronic processes. While elementary bricks of the VHE emission scenarios seem now reasonably well identified, a global picture of these sources, describing the geometry and dynamics of the VHE zone, is not yet available. Multiwavelength monitoring and global alert network will be important to better constrain the picture, especially with the perspective of CTA, a major project of the next generation in ground-based gamma-ray astronomy.

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Adriani, O., Y. Akaike, K. Asano, Y. Asaoka, E. Berti, G. Bigongiari, W. R. Binns et al. "CALET Search for Electromagnetic Counterparts of Gravitational Waves during the LIGO/Virgo O3 Run". Astrophysical Journal 933, n. 1 (1 luglio 2022): 85. http://dx.doi.org/10.3847/1538-4357/ac6f53.

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Abstract The CALorimetric Electron Telescope (CALET) on the International Space Station consists of a high-energy cosmic-ray CALorimeter (CAL) and a lower-energy CALET Gamma-ray Burst Monitor (CGBM). CAL is sensitive to electrons up to 20 TeV, cosmic-ray nuclei from Z = 1 through Z ∼ 40, and gamma rays over the range 1 GeV–10 TeV. CGBM observes gamma rays from 7 keV to 20 MeV. The combined CAL-CGBM instrument has conducted a search for gamma-ray bursts (GRBs) since 2015 October. We report here on the results of a search for X-ray/gamma-ray counterparts to gravitational-wave events reported during the LIGO/Virgo observing run O3. No events have been detected that pass all acceptance criteria. We describe the components, performance, and triggering algorithms of the CGBM—the two Hard X-ray Monitors consisting of LaBr3(Ce) scintillators sensitive to 7 keV–1 MeV gamma rays and a Soft Gamma-ray Monitor BGO scintillator sensitive to 40 keV–20 MeV—and the high-energy CAL consisting of a charge detection module, imaging calorimeter, and the fully active total absorption calorimeter. The analysis procedure is described and upper limits to the time-averaged fluxes are presented.

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Ivanova, A. L., R. Monkhoev, I. Astapov, P. Bezyazeekov, M. Blank, E. Bonvech, A. Borodin et al. "Tunka-Grande scintillation array: resent results". Journal of Physics: Conference Series 2156, n. 1 (1 dicembre 2021): 012196. http://dx.doi.org/10.1088/1742-6596/2156/1/012196.

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Abstract Objectives of the TAIGA Astrophysical complex include the study of the flux of charged cosmic rays and diffuse gamma rays with energies above 100 TeV. This complex is located in the Tunka Valley about 50 km from Lake Baikal at the site of the Tunka-133 Cherenkov facility. TAIGA includes the TAIGA-HiSCORE wide-angle Cherenkov array, the network of Imaging Atmospheric Cherenkov Telescopes (TAIGA-IACT), the Tunka-Grande and TAIGA-Muon scintillation arrays. In this work, we present the results of an analysis of the joint events of the Tunka-Grande scintillation array and TAIGA-HiSCORE and Tunka-133 Cherenkov facilities. The results verify sufficient accuracy of the scintillation experiment for the hybrid study of mass composition of cosmic rays and gamma-hadron separation.

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Hassan, Sajad Kareem Khalaf, Sajad Riad Kiridi Hajm, Muntazir Kazim Eabd Alamir Hasuwn e Zahraa Jasim Mohammed. "DISEASES THAT ARE DIAGNOSED AND TREATED BY X-RAYS AND GAMMA RAYS". European Journal of Medical Genetics and Clinical Biology 1, n. 7 (6 luglio 2024): 43–60. http://dx.doi.org/10.61796/jmgcb.v1i7.713.

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rays have long been one of the most effective tools in detecting and diagnosing diseases because of their effective and practical properties in diagnosing the various diseases that appear in the x-ray image. Diagnostic x- rays are considered an examination carried out using To see the internal anatomy of the body Accurately and pinpoint the tiny spots. The x-ray beam passes through the body, and is absorbed in different quantities, depending on the absorption capacity of the material. Dense materials such as bones and metal appear in white in the x-ray image, while air in the lungs appears in black, and muscles and fat appear in shades of grey. In some tests, we resort to introducing contrast dyes such as iodine or barium into the body to provide more details of the part to be imaged, such as imaging the bile ducts, spinal cord (myelography), urinary tract, and other parts that need the use of contrast dyes. in These methods enabled us to diagnose various diseases such as chest diseases and various cancers If a foreign body is detected or calcium calcifications are seen.

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Song, Y., M. Zhang, B. J. Duan, W. P. Yan, L. Sheng, G. Z. Song, J. M. Ma, C. C. Han e Z. M. Yao. "A high-speed radiation imaging system based on liquid scintillator filled capillary arrays". Review of Scientific Instruments 93, n. 3 (1 marzo 2022): 033702. http://dx.doi.org/10.1063/5.0066686.

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A high-speed radiation imaging system based on an image converter of liquid scintillator filled capillary arrays has been developed, which is sensitive to x rays, gamma rays, and neutrons. This imaging system has advantages of both high spatial resolution and high sensitivity because increasing the thickness of the image converter only leads to little deterioration on imaging resolution. The capillary arrays have dimensions of 150 mm diameter and 50 mm thickness, with 100 µm diameter of each capillary. The fluorescence decay time of the filled liquid scintillator based on the mixture of p-xylene and 2,5-diphenyloxazole has been evaluated to be ∼3 ns with the single photon method under the gamma ray excitation. The spatial resolution has been experimentally evaluated to be about 1.15 and 0.6 mm, under excitation of x rays and neutrons, respectively. The imaging system has been applied for diagnosing the dynamic x-ray spot generated by the rod pinch. Two frames in single shot with 15 ns temporal resolution and 20 ns inter-frame separation time have been obtained, which show the spatiotemporal distribution of the electrons bombarding the tungsten rod, indicating the ability of this imaging system in diagnosing dynamic radiation objects. In addition, the technique of capillary arrays provides a promising path for applications of advanced liquid scintillators in the field of radiation imaging.

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Pestotnik, R., G. Razdevšek, R. Dolenec, G. El Fakhri, P. Križan, S. Majewski, A. Studen e S. Korpar. "Simulation study of a 50 ps panel TOF PET imager". Journal of Instrumentation 17, n. 12 (1 dicembre 2022): C12010. http://dx.doi.org/10.1088/1748-0221/17/12/c12010.

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Abstract Positron emission tomography (PET) is one of the most important diagnostic tools in medicine, providing three-dimensional imaging of functional processes in the body. The method is based on detecting two gamma rays originating from the point of annihilation of the positron emitted by a radio-labeled agent and used to follow the human’s physiological processes. In Time-Of-Flight PET, gamma rays’ arrival time is measured in addition to their position. The coincidence timing resolution (CTR) of state-of-the-art scanners is between 200 ps and 500 ps FWHM, which can significantly improve the contrast in imaging large objects. However, increasing the sensitivity of the next-generation PET scanners requires increasing the imaging device’s timing accuracy. Using the latest advances, a multichannel system with improved CTR is becoming technologically possible. Generally, 3D images from limited angle PET scanners are distorted and have artifacts. Fortunately, with improving timing resolution of PET gamma detectors, artifact-free images can be obtained even by a very simplified detector. We were studying a simple panel PET detector consisting of gamma detectors with 50 ps coincidence timing resolution. With this new concept, the price of PET scanners for imaging single or multiple organs can be drastically decreased. We evaluated different panel detector arrangements by imaging different phantoms. The reconstructed images were compared with those obtained with the Siemens Biograph Vision, a state-of-the-art clinical PET scanner. We found comparable image quality parameters of both systems when the CTR approaches 50 ps FWHM and that good CTR can partially compensate for smaller gamma detection efficiency.

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Dominis Prester, Dijana, Jan Ebr, Markus Gaug, Alexander Hahn, Ana Babić, Jiří Eliášek, Petr Janeček et al. "Characterisation of the Atmosphere in Very High Energy Gamma-Astronomy for Imaging Atmospheric Cherenkov Telescopes". Universe 10, n. 9 (30 agosto 2024): 349. http://dx.doi.org/10.3390/universe10090349.

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Ground-based observations of Very High Energy (VHE) gamma rays from extreme astrophysical sources are significantly influenced by atmospheric conditions. This is due to the atmosphere being an integral part of the detector when utilizing Imaging Atmospheric Cherenkov Telescopes (IACTs). Clouds and dust particles diminish atmospheric transmission of Cherenkov light, thereby impacting the reconstruction of the air showers and consequently the reconstructed gamma-ray spectra. Precise measurements of atmospheric transmission above Cherenkov observatories play a pivotal role in the accuracy of the analysed data, among which the corrections of the reconstructed energies and fluxes of incoming gamma rays, and in establishing observation strategies for different types of gamma-ray emitting sources. The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the Cherenkov Telescope Array Observatory (CTAO), both located on the Observatorio del Roque de los Muchachos (ORM), La Palma, Canary Islands, use different sets of auxiliary instruments for real-time characterisation of the atmosphere. In this paper, historical data taken by MAGIC LIDAR (LIght Detection And Ranging) and CTAO FRAM (F/Photometric Robotic Telescope) are presented. From the atmospheric aerosol transmission profiles measured by the MAGIC LIDAR and CTAO FRAM aerosol optical depth maps, we obtain the characterisation of the clouds above the ORM at La Palma needed for data correction and optimal observation scheduling.

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26

Geppert-Kleinrath, V., N. Hoffman, N. Birge, A. DeYoung, D. Fittinghoff, M. Freeman, H. Geppert-Kleinrath et al. "Gamma-ray imaging of inertial confinement fusion implosions reveals remaining ablator carbon distribution". Physics of Plasmas 30, n. 2 (febbraio 2023): 022703. http://dx.doi.org/10.1063/5.0122938.

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The joint LANL/LLNL nuclear imaging team has acquired the first gamma-ray images of inertial confinement fusion implosions at the National Ignition Facility. The gamma-ray image provides crucial information to help characterize the inertially confined fuel and ablator assembly at stagnation, information that would be difficult to acquire from neutron or x-ray observations. Gamma imaging visualizes both gamma radiation emitted directly in deuterium–tritium (DT) fusion reactions as well as gamma rays produced when DT fusion neutrons scatter inelastically on carbon nuclei in the remaining ablator of the fuel capsule. The resulting image provides valuable information on the position and density of the remaining ablator and potential contamination of the hot spot—a powerful diagnostic window into the capsule assembly during burn.

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27

Starič, M., S. Korpar, D. Korbar e A. Stanovnik. "A thin multiwire proportional chamber for imaging with UV light, X-rays and gamma rays". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 323, n. 1-2 (dicembre 1992): 91–96. http://dx.doi.org/10.1016/0168-9002(92)90274-8.

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28

Zhang, Changqing, Liang Sheng, Zhaohui Song, Tianxing Da, Haoqing Li, Baojun Duan, Yang Li, Dongwei Hei e Qunshu Wang. "Experimental Demonstration of a Tunable Energy-Selective Gamma-Ray Imaging System Based on Recoil Electrons". Sensors 24, n. 12 (8 giugno 2024): 3736. http://dx.doi.org/10.3390/s24123736.

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The domain of gamma-ray imaging necessitates technological advancements to surmount the challenge of energy-selective imaging. Conventional systems are constrained in their dynamic focus on specific energy ranges, a capability imperative for differentiating gamma-ray emissions from diverse sources. This investigation introduces an innovative imaging system predicated on the detection of recoil electrons, addressing the demand for adjustable energy selectivity. Our methodology encompasses the design of a gamma-ray imaging system that leverages recoil electron detection to execute energy-selective imaging. The system’s efficacy was investigated experimentally, with emphasis on the adaptability of the energy selection window. The experimental outcomes underscore the system’s adeptness at modulating the energy selection window, adeptly discriminating gamma rays across a stipulated energy spectrum. The results corroborate the system’s adaptability, with an adjustable energy resolution that coincides with theoretical projections and satisfies the established criteria. This study affirms the viability and merits of utilizing recoil electrons for tunable energy-selective gamma-ray imaging. The system’s conceptualization and empirical validation represent a notable progress in gamma-ray imaging technology, with prospective applications extending from medical imaging to astrophysics. This research sets a solid foundation for subsequent inquiries and advancements in this domain.

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29

Carnes, Bruce A., e Thomas E. Fritz. "Continuous Irradiation of Beagles with Gamma Rays". Radiation Research 136, n. 1 (ottobre 1993): 103. http://dx.doi.org/10.2307/3578646.

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30

Aharonian, F., F. Ait Benkhali, J. Aschersleben, M. Böttcher, M. Backes, V. Barbosa Martins, R. Batzofin et al. "Search for the evaporation of primordial black holes with H.E.S.S." Journal of Cosmology and Astroparticle Physics 2023, n. 04 (1 aprile 2023): 040. http://dx.doi.org/10.1088/1475-7516/2023/04/040.

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Abstract Primordial Black Holes (PBHs) are hypothetical black holes predicted to have been formed from density fluctuations in the early Universe. PBHs with an initial mass around 1014–1015 g are expected to end their evaporation at present times in a burst of particles and very-high-energy (VHE) gamma rays. Those gamma rays may be detectable by the High Energy Stereoscopic System (H.E.S.S.), an array of imaging atmospheric Cherenkov telescopes. This paper reports on the search for evaporation bursts of VHE gamma rays with H.E.S.S., ranging from 10 to 120 seconds, as expected from the final stage of PBH evaporation and using a total of 4816 hours of observations. The most constraining upper limit on the burst rate of local PBHs is 2000 pc-3 yr-1 for a burst interval of 120 seconds, at the 95% confidence level. The implication of these measurements for PBH dark matter are also discussed.

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31

Hong, Seung Han, Wook Jae Yoo, Sang Hun Shin, Hyeok In Sim, Seon Guen Kim, Hye Su Jeon, Jae Seok Jang et al. "Comparison of Optical and Scintillation Images Obtained by Using a Fiber-Optic Beta/Gamma Imaging Detector". Advanced Materials Research 1083 (gennaio 2015): 137–41. http://dx.doi.org/10.4028/www.scientific.net/amr.1083.137.

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We developed a fiber-optic beta/gamma imaging detector that can obtain the scintillating images for beta-or gamma-ray emitted from the radioisotope. To evaluate spatial resolution of proposed imaging detector, we obtained the optical images using USAF 1951 resolution target. And then, a modulation transfer function curve of the optical image was calculated. Also, we measured the scintillating images of Tl-204 and Cs-137 with information respecting the beta-and gamma-rays distribution. Finally, the intensities of scintillating light as a function of radioactivity were analyzed from the region of interest in the scintillating image.

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32

Prester, D. Dominis, J. Sitarek, J. Becerra, S. Buson, E. Lindfors, M. Manganaro, D. Mazin et al. "MAGIC detection of sub-TEV emission from gravitationally lensed blazar QSO B0218+357". Proceedings of the International Astronomical Union 12, S324 (settembre 2016): 235–36. http://dx.doi.org/10.1017/s1743921317002344.

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The blazar QSO B0218+357 is the first gravitationally lensed blazar detected in the very high energy (VHE, E > 100 GeV) gamma-ray spectral range (Ahnen et al. 2016). It is gravitationally lensed by the intervening galaxy B0218+357G (zl = 0.68466 ± 0.00004, Carilli et al. 1993), which splits the blazar emission into two components, spatially indistinguishable by gamma-ray instruments, but separated by a 10-12 days delay. In July 2014 a flare from QSO B0218+357 was observed by the Fermi-LAT (Large Area Telescope, Atwood et al. 2009, Ackermann et al. 2012), and followed-up by the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes, a stereoscopic system of two 17m Imaging Atmospheric Cherenkov Telescopes located on La Palma, Canary Islands (Aleksić et al. 2016a, 2016b), during the expected time of arrival of the delayed component of the emission. MAGIC could not observe the leading image due to the Full Moon. The MAGIC and Fermi-LAT observations were accompanied by optical data from KVA telescope at La Palma, and X-ray observations by Swift-XRT (Fig. 1 left). Variability in gamma-rays was of the order of one day, while no variability correlated with gamma-rays was observed at lower energies. The flux ratio of the leading to trailing image in HE gamma-rays was larger than in the flare of QSO B0218+357 observed by Fermi-LAT in 2012 (Cheung et al. 2014). Changes in the observed flux ratio can be caused by gravitational microlensing on individual stars in the host galaxy (Neronov et al. 2015), or by other compact objects like for ex. clumps in giant molecular clouds (Sitarek & Bednarek 2016).

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33

Tanimori, Toru. "Detection of TeV Gamma Rays from SN1006". Symposium - International Astronomical Union 188 (1998): 121–24. http://dx.doi.org/10.1017/s0074180900114585.

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In spite of the recent progress of high energy gamma-ray astronomy, there still remains quite unclear and important problem about the origin of cosmic rays. Supernova remnants (SNRs) are the favoured site for cosmic rays up to 1016 eV, as they satisfy the requirements such as an energy input rate. But direct supporting evidence is sparse. Recently intense non-thermal X-ray emission from the rims of the Type Ia SNR SN1006 (G327.6+14.6) has been observed by ASCA (Koyama et al. 1995)and ROSAT (Willingale et al. 1996), which is considered, by attributing the emission to synchrotron radiation, to be strong evidence of shock acceleration of high energy electrons up to ~100 TeV. If so, TeV gamma rays would also be expected from inverse Compton scattering (IC) of low energy photons (mostly attributable to the 2.7 K cosmic background photons) by these electrons. By assuming the magnetic field strength (B) in the emission region of the SNR, several theorists (Pohl 1996; Mastichiadis 1996; Mastichiadis & de Jager 1996; Yoshida & Yanagita 1997) calculated the expected spectra of TeV gamma rays using the observed radio/X-ray spectra. Observation of TeV gamma rays would thus provide not only the further direct evidence of the existence of very high energy electrons but also the another important information such as the strength of the magnetic field and diffusion coefficient of the shock acceleration. With this motivation, SN1006 was observed by the CANGAROO imaging air Cerenkov telescope in 1996 March and June, also 1997 March and April.

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34

Martin, J. B., G. F. Knoll, D. K. Wehe, N. Dogan, V. Jordanov, N. Petrick e M. Singh. "A ring Compton scatter camera for imaging medium energy gamma rays". IEEE Transactions on Nuclear Science 40, n. 4 (agosto 1993): 972–78. http://dx.doi.org/10.1109/23.256695.

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35

Fisher, T. R., J. W. Hamilton, J. D. Hawley, J. R. Kilner, M. J. Murphy e G. H. Nakano. "Imaging of gamma rays with the WINKLER high-resolution germanium spectrometer". IEEE Transactions on Nuclear Science 37, n. 3 (giugno 1990): 1483–89. http://dx.doi.org/10.1109/23.57405.

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36

Lemoine-Goumard, Marianne. "Gamma-ray observations of supernova remnants". Proceedings of the International Astronomical Union 9, S296 (gennaio 2013): 287–94. http://dx.doi.org/10.1017/s1743921313009605.

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AbstractIn the past few years, gamma-ray astronomy has entered a golden age. At TeV energies, only a handful of sources were known a decade ago, but the current generation of ground-based imaging atmospheric Cherenkov telescopes has increased this number to more than one hundred. At GeV energies, the Fermi Gamma-ray Space Telescope has increased the number of known sources by nearly an order of magnitude in its first 2 years of operation. The recent detection and unprecedented morphological studies of gamma-ray emission from shell-type supernova remnants is of great interest, as these analyses are directly linked to the long standing issue of the origin of the cosmic-rays. However, these detections still do not constitute a conclusive proof that supernova remnants accelerate the bulk of Galactic cosmic-rays, mainly due to the difficulty of disentangling the hadronic and leptonic contributions to the observed gamma-ray emission. In the following, I will review the most relevant results of gamma ray astronomy concerning supernova remnants (shell-type and middle-age interacting with molecular clouds).

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37

Vasiljević, Jana, e Bo Cederwall. "Performance Evaluation of an Imaging Radiation Portal Monitor System". Applied Sciences 12, n. 18 (7 settembre 2022): 9001. http://dx.doi.org/10.3390/app12189001.

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An organic scintillator-based radiation portal monitor (RPM) prototype system with imaging capabilities has been developed based on the neutron–gamma emission tomography technique. The technique enables rapid detection and precise location of small amounts of special nuclear materials, such as plutonium, using time and energy correlations between fast neutrons and gamma rays from spontaneous fission with low false-alarm rates. These capabilities, in addition to state-of-the-art detection of various gamma-emitting sources, enables the novel imaging RPM concept to efficiently address global security threats from terrorism and the proliferation of nuclear weapons. The detector approach is simple and versatile and can easily be adapted for different applications in nuclear security, public safety, nuclear emergency response, and radiological surveying. In this work, basic performance parameters of the imaging RPM prototype system developed at KTH have been evaluated.

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38

A. M Issa, Shams, Antoaneta Ene e Hesham M. H. Zakaly. "Evaluating the Effectiveness of Tellurium-Molybdenum Oxide Glass Systems for Radiation Shielding Protection". Multidisciplinary Materials Chronicles 1, n. 1 (aprile 2024): 19–29. http://dx.doi.org/10.62184/mmc.jmmc110020242.

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The present investigation examined TeO2–MeO3 glasses with different compositions for their ability to absorb γ-rays using the Phy-X and FLUKA Code, respectively. The study covered energies ranging from 0.015 to 15 MeV, where several parameters such as effective atomic number (Zeff), free path mean (GMFP), mass attenuation coefficient (GMAC), macroscopic cross-section (GLAC), and half-value levels were analyzed (GHVL). Glass composite composed of 80% TeO2 and 20% MoO3 was found to have the lowest GLAC content among the tested samples. GHVL = 0.055 cm was the half-value of the 80TeO2–20MoO3 glasses when they were subjected to 80 keV gamma-rays. It is anticipated that the GMFP of the investigated materials ranges from 0.004 to 0.005 cm when subjected to 100 keV gamma-rays. It was said that the increase in Zeff may be attributed to an increased quantity of electrons that were accessible for interaction with photons, resulting in a decreased probability of gamma rays passing through the shielding material. The cumulative impact of these findings demonstrates that specific glass compositions, particularly those that include Tellurium, have the potential to be used as excellent radiation shielding materials. These materials are becoming more important for providing efficient radiation protection in various industries and applications, including medical imaging, nuclear power, and space exploration.

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39

Zhang, Xi, Qiangqiang Xie, Siwei Xie, Xin Yu, Jianfeng Xu e Qiyu Peng. "A Novel Portable Gamma Radiation Sensor Based on a Monolithic Lutetium-Yttrium Oxyorthosilicate Ring". Sensors 21, n. 10 (12 maggio 2021): 3376. http://dx.doi.org/10.3390/s21103376.

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Abstract (sommario):

Portable radiation detectors are widely used in environmental radiation detection and medical imaging due to their portability feature, high detection efficiency, and large field of view. Lutetium-yttrium oxyorthosilicate (LYSO) is a widely used scintillator in gamma radiation detection. However, the structure and the arrangement of scintillators limit the sensitivity and detection accuracy of these radiation detectors. In this study, a novel portable sensor based on a monolithic LYSO ring was developed for the detection of environmental radiation through simulation, followed by construction and assessments. Monte Carlo simulations were utilized to prove the detection of gamma rays at 511 keV by the developed sensor. The simulations data, including energy resolutions, decoding errors, and sensitivity, showed good potential for the detection of gamma rays by the as-obtained sensor. The experimental results using the VA method revealed decoding errors in the energy window width of 50 keV less than 2°. The average error was estimated at 0.67°, a sufficient value for the detection of gamma radiation. In sum, the proposed radiation sensor appears promising for the construction of high-performance radiation detectors and systems.

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40

Omori, Y., S. Inoue, T. Otsuka, Y. Nagamatsu, A. Sorimachi e T. Ishikawa. "REDUCTION IN AMBIENT GAMMA DOSE RATE FROM RADIOCESIUM DUE TO SNOW COVER". Radiation Protection Dosimetry 184, n. 3-4 (30 aprile 2019): 510–13. http://dx.doi.org/10.1093/rpd/ncz091.

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Abstract In the present study, variations in ambient gamma dose rate associated with snow cover were examined in a radioactive-contaminated site in Fukushima Prefecture, Japan. The ambient gamma dose rates decreased with increasing snow depth. The reduction trends were different between fresh snow (0.1–0.2 g/cm3) and granular snow (0.3–0.4 g/cm3) depending on snow density. Snow cover water content (snow water equivalent) calculated from snow depth and density was a key parameter governing the reduction in the ambient gamma dose rate. The ambient gamma dose rates reduced to 0.6 and 0.5 at 4 g/cm2 and 8 g/cm2 of snow water equivalent, respectively. Based on gamma-ray flux density distributions, the ambient gamma dose rates from the primary gamma rays decreased more compared to those from scattered gamma rays due to snow cover.

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41

Poirier, Yannick, Matthew D. Belley, Mark W. Dewhirst, Terry T. Yoshizumic e Julian D. Down. "Transitioning from Gamma Rays to X Rays for Comparable Biomedical Research Irradiations: Energy Matters". Radiation Research 193, n. 6 (21 aprile 2020): 506. http://dx.doi.org/10.1667/rade-20-00039.1.

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42

Ando, Koichi, Yukari Yoshida, Ryoichi Hirayama, Sachiko Koike e Naruhiro Matsufuji. "Dose- and LET-dependent changes in mouse skin contracture up to a year after either single dose or fractionated doses of carbon ion or gamma rays". Journal of Radiation Research 63, n. 2 (10 gennaio 2022): 221–29. http://dx.doi.org/10.1093/jrr/rrab123.

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Abstract Time dependence of relative biological effectiveness (RBE) of carbon ions for skin damage was investigated to answer the question of whether the flat distribution of biological doses within a Spread-Out Bragg peak (SOBP) which is designed based on in vitro cell kill could also be flat for in vivo late responding tissue. Two spots of Indian ink intracutaneously injected into the legs of C3H mice were measured by calipers. An equieffective dose to produce 30% skin contraction was calculated from a dose–response curve and used to calculate the RBE of carbon ion beams. We discovered skin contraction progressed after irradiation and then reached a stable/slow progression phase. Equieffective doses decreased with time and the decrease was most prominent for gamma rays and least prominent for 100 keV/μm carbon ions. Survival parameter of alpha but not beta in the linear-quadratic model is closely related to the RBE of carbon ions. Biological doses within the SOBP increased with time but their distribution was still flat up to 1 year after irradiation. The outcomes of skin contraction studies suggest that (i) despite the higher RBE for skin contracture after carbon ions compared to gamma rays, gamma rays can result in a more severe late effect of skin contracture. This is due to the carbon effect saturating at a lower dose than gamma rays, and (ii) the biological dose distribution throughout the SOBP remains approximately the same even one year after exposure.

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43

FitzGerald, J. G. M., L. W. Burggraf, B. R. Kowash e E. L. Hull. "A Modulating Liquid Collimator for Coded Aperture Adaptive Imaging of Gamma-Rays". IEEE Transactions on Nuclear Science 60, n. 3 (giugno 2013): 2300–2307. http://dx.doi.org/10.1109/tns.2013.2259052.

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44

Ferrando, P., G. Comby, P. Goret, N. Petrou, A. Tabary e A. Zadra. "A cherenkov imaging technique for the detection of high energy gamma-rays". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 260, n. 2-3 (ottobre 1987): 501–8. http://dx.doi.org/10.1016/0168-9002(87)90123-9.

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Zhu, Xuping, e Georges El Fakhri. "Monte Carlo modeling of cascade gamma rays in86Y PET imaging: preliminary results". Physics in Medicine and Biology 54, n. 13 (12 giugno 2009): 4181–93. http://dx.doi.org/10.1088/0031-9155/54/13/014.

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46

Sato, Yuri, Kaori Obayashi, Ryo Yamazaki, Kohta Murase e Yutaka Ohira. "Off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst GRB 190829A". Monthly Notices of the Royal Astronomical Society 504, n. 4 (7 maggio 2021): 5647–55. http://dx.doi.org/10.1093/mnras/stab1273.

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ABSTRACT Recently, ground-based Imaging Atmospheric Cherenkov Telescopes have reported the detection of very-high-energy (VHE) gamma-rays from some gamma-ray bursts (GRBs). One of them, GRB 190829A, was triggered by the Swift satellite, and about 2 × 104 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ∼5σ significance. This event had unusual features of having much smaller isotropic equivalent gamma-ray energy than typical long GRBs and achromatic peaks in X-ray and optical afterglow at about 1.4 × 103 s. Here, we propose an off-axis jet scenario that explains these observational results. In this model, the relativistic beaming effect is responsible for the apparently small isotropic gamma-ray energy and spectral peak energy. Using a jetted afterglow model, we find that the narrow jet, which has the initial Lorentz factor of 350 and the initial jet opening half-angle of 0.015 rad, viewed off-axis can describe the observed achromatic behaviour in the X-ray and optical afterglow. Another wide, baryon-loaded jet is necessary for the later-epoch X-ray and radio emissions. According to our model, the VHE gamma rays observed by H.E.S.S. at 2 × 104 s may come from the narrow jet through the synchrotron self-Compton process.

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47

Fariña, Luis, Keerthana Lathika, Giulio Lucchetta, Monong Yu, Joan Boix, Laia Cardiel-Sas, Oscar Blanch, Manel Martinez e Javier Rico. "Design and Performance of a Low-Energy Gamma-Ray Trigger System for HERD". Instruments 8, n. 2 (4 maggio 2024): 31. http://dx.doi.org/10.3390/instruments8020031.

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The High Energy cosmic-Radiation Detection (HERD) facility has been proposed as one of the main experiments on board the Chinese space station. HERD is scheduled to be installed around 2027 and to operate for at least 10 years. Its main scientific goals are the study of the cosmic ray spectrum and composition up to the PeV energy range, indirect dark matter detection, and all-sky gamma-ray observation above 100 MeV. HERD features a novel design in order to optimize its acceptance per weight, with a central 3D imaging calorimeter surrounded on top and on its four lateral sides by complementary subdetectors. A dedicated trigger, dubbed the ultra-low-energy gamma-ray (ULEG) trigger, is required to enable the detection of gamma rays down to ~100 MeV. The ULEG trigger design is based upon the search for energy deposition patterns on the tracker and the anticoincidence shield, compatible with the conversion of a gamma ray within the tracker volume and resulting in enough tracker hits to allow for a good-quality gamma-ray direction reconstruction. We describe the current status of the design of the ULEG trigger system. We also characterize its performance in detecting gamma rays as inferred from Monte Carlo studies.

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Chowdhury, Talal Ahmed, Saquib Hassan, Jahid Hossain, Salah Nasri e Mahmud Ashraf Shamim. "Probing the Dark Matter of the Three-loop Radiative Neutrino Mass Generation Model with the Cherenkov Telescope Array". Journal of Physics: Conference Series 2156, n. 1 (1 dicembre 2021): 012076. http://dx.doi.org/10.1088/1742-6596/2156/1/012076.

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Abstract We investigate the prospect of detecting the Dark Matter (DM) candidate in the three-loop radiative neutrino mass generation model extended with large electroweak multiplets of the Standard Model (SM) gauge group, at the future imaging atmospheric Cherenkov telescope known as the Cherenkov Telescope Array (CTA). We find that the addition of such large electroweak multiplets leads to a sizable Sommerfeld enhanced annihilation of the DM with O(TeV) mass, into the SM gauge bosons which results in continuum and line-like spectra of very high energy (VHE) gamma-rays, and therefore becomes observable for the CTA. By considering the continuum VHE gamma-rays produced from the DM annihilation at the Galactic center, we probe the parameter space of the model using the sensitivity reach of the CTA.

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Straume, Tore. "High-Energy Gamma Rays in Hiroshima and Nagasaki". Health Physics 69, n. 6 (dicembre 1995): 954–56. http://dx.doi.org/10.1097/00004032-199512000-00010.

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50

Tomoda, T., M. Arimoto, T. Mizuno, D. Sato, F. Lucyana, J. Kataoka, M. Kato et al. "Multi-pixel photon counter-based gamma camera with pinhole collimator to locate Cs-137 sources at high dose rates for the Fukushima nuclear power plant". Journal of Instrumentation 19, n. 02 (1 febbraio 2024): C02032. http://dx.doi.org/10.1088/1748-0221/19/02/c02032.

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Abstract The Fukushima Daiichi Nuclear Power Plant was severely damaged during the 2011 Great East Japan Earthquake. However, the ongoing decommissioning work has been limited by the complexity of the reactor's internal structure and very high radiation levels; locating radioactive sources is essential for efficient decommissioning. Conventional gamma cameras are mainly designed for low radiation dose (∼mSv/h) and using them under high radiation conditions is difficult (>Sv/h). Therefore, we developed a pinhole gamma camera with a gamma radiation detector consisting of a high-speed YGAG scintillator array and multi-pixel photon counters to locate radioactive sources at high dose rates. The gamma-ray photon signals captured by the developed two-dimensional detector array can be processed at a speed as high as >1 MHz/pixel using the developed large scale integrated circuit. Herein, we report the measurement results of an extremely high radioactivity of 137Cs (∼34 TBq) using the developed gamma camera. The gamma-ray source position was determined using an angular size of ∼4.6°, with images obtained at 2 m from the radioactive source and at a dose rate of 0.3 Sv/h. The direct gamma rays with a photoelectric peak at 662 keV and scattered component of gamma rays can be distinguished from the measured spectrum. We also characterize the imaging capability of the 137Cs depending on the detected gamma-ray energies and discuss related details.

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