Gamma-ray Sources Research Articles

Attempt to re-estimate organ doses of victims in non-homogeneous exposure accident by means of the state-of-the-art Mesh-type Reference Computational Phantom-a case study of an IR-192 source accident.

An attempt was made to estimate organ doses of a victim in a high-dose non-homogeneous exposure accident caused by a sealed 192Ir gamma-ray source. The Gilan accident was selected as a case study. Organ doses including testis, red bone marrow and so on were properly estimated by applying the Monte Carlo calculation with the state-of-the-art adult male Mesh type Reference Computational Phantom. By introducing a complicated exposure scenario, the dose distribution on the right chest of the victim in the Gilan accident could be reproduced to a certain extent.

Influence of the gamma source on the radiolytic stability of N,N,N′,N′-tetra-n-octyl-diglycolamide (TODGA)

Abstract In nuclear reprocessing, hydrolytic and radiolytic stability of ligands, extractants, diluents and solvents is of particular importance. The strength of extraction systems can only be fully exploited when process conditions are predictable and essential molecules, which are in close proximity to radioactive isotopes, are resistant to the radiation. During the development of novel extraction systems, testing of the radiolytic stability is often evaluated by exposing the molecules to high energetic gamma rays. In this work, the influence of the source of gamma rays is evaluated. TODGA was irradiated from 0–500 kGy using different sources of gamma rays, and its degradation was followed using UPLC-HRMS. Pool-type gamma irradiation facilities BRIGITTE B (Co-60) and GEUSE II (spent nuclear fuel) at SCK CEN were employed to serve as gamma sources. In this work, it is found that there is no significant influence on TODGA degradation which can be attributed to the origin of the gamma source.

Search for Joint Multimessenger Signals from Potential Galactic Cosmic-Ray Accelerators with HAWC and IceCube

The origin of high-energy galactic cosmic rays is yet to be understood, but some galactic cosmic-ray accelerators can accelerate cosmic rays up to PeV energies. The high-energy cosmic rays are expected to interact with the surrounding material or radiation, resulting in the production of gamma-rays and neutrinos. To optimize for the detection of such associated production of gamma-rays and neutrinos for a given source morphology and spectrum, a multimessenger analysis that combines gamma-rays and neutrinos is required. In this study, we use the Multi-Mission Maximum Likelihood framework with IceCube Maximum Likelihood Analysis software and HAWC Accelerated Likelihood to search for a correlation between 22 known gamma-ray sources from the third HAWC gamma-ray catalog and 14 yr of IceCube track-like data. No significant neutrino emission from the direction of the HAWC sources was found. We report the best-fit gamma-ray model and 90% CL neutrino flux limit from the 22 sources. From the neutrino flux limit, we conclude that, for five of the sources, the gamma-ray emission observed by HAWC cannot be produced purely from hadronic interactions. We report the limit for the fraction of gamma-rays produced by hadronic interactions for these five sources.

Design and Construction of Experimental System for Validation of a New Image Reconstruction Technique with Limited-view-angle Projection Data for BNCT-SPECT

Abstract. Boron Neutron Capture Therapy (BNCT) is expected to be a promising radiation therapy for cancer, and research on various issues associated with it is still in progress. One of the unsolved issues is the construction of a system for observing the effect of the treatment (local boron dose) in real time under high-background circumstances. Thus, we set out to establish a method for measuring gamma-rays emitted promptly from the body following the boron neutron capture reaction and reconstructing images in a SPECT-like manner. We call this method BNCT-SPECT. We have been developing a new image reconstruction method based on Bayesian estimation for the BNCT-SPECT method. In the present study, the aims were to design and construct an experimental system capable of validating BNCT-SPECT and its image reconstruction method and to confirm BNCT-SPECTs performance. The crucial takeaway from this study is that we should consider the use of extremely high background radiation during BNCT. For the validation of BNCT-SPECT, we attempted to reproduce these conditions, despite this being quite challenging. We first constructed an experimental system capable of reproducing such conditions. Theoretical investigation was carried out to facilitate the design of the system using the Monte Carlo transport calculation code MCNP. Finally, we performed experiments with some standard gamma-ray sources to complete the system.

Overestimation of Astrophysical Gamma-Ray Energies during Thunderstorms: Synergy of Galactic and Atmospheric Accelerators

Particle accelerators abound in space plasmas, saturating the cosmos with fully stripped nuclei and gamma rays, with energies surpassing the capabilities of human-made accelerators by orders of magnitude. Upon reaching Earth’s atmosphere, these particles trigger extensive air showers (EASs), generating millions of secondary cosmic rays of lower energies. Free electrons from EASs developing in the atmosphere are seeds for atmospheric electron accelerators. Strong atmospheric electric fields (AEFs) evolving during thunderstorms act as accelerators, amplifying the intensity of electrons many times, significantly enlarging the EAS size (number of electrons). Thus, the energy of the primary cosmic ray recovered by EAS size can be significantly overestimated. Recently discovered by high-altitude EAS arrays, PeVatron candidates (ultra–high-energy (UHE) astrophysical gamma-ray sources) must be carefully examined according to the atmospheric conditions during EAS detection. Large High Altitude Air Shower Observatory and High-Altitude Water Cherenkov Observatory arrays are located in regions of frequent thunderstorms, and an AEF’s strength can reach and surpass the critical strength to start relativistic runaway electron avalanches. A few registered UHE gamma rays from stellar sources can be registered at just this time when the AEF highly enhances the EAS size. Thunderstorm ground enhancements are copiously registered at mountain peaks of Eastern Europe, Germany, and Armenia, with energies well above the threshold energy of EAS array scintillators. Thus, the overestimation of the energy of primary particles is not an exotic process but a consequence of already well-established physical phenomena. Consequently, a report on each registered UHE gamma ray should include the recorded time and corresponding weather conditions.

Enhancing shielding efficiency of ordinary and barite concrete in radiation shielding utilizations

Concrete has been widely utilized as a radiation shielding material due to its properties and structural integrity. This study aims to evaluate the efficiency of ordinary concrete versus barite concrete as radiation shielding materials, focusing on the physical aspects and changes in crystal size lattice parameters after neutron irradiation. Specifically, the research investigates the shielding effectiveness of these materials across different grades (M15, M25, M35, and M45) against gamma-ray sources Cobalt-60 and Caesium-137. The methodology involves measuring the linear attenuation coefficient (μ), half value layer (HVL), tenth value layer (TVL), and mean free path (MFP). Additionally, X-ray diffraction (XRD) was employed to assess crystallite size and lattice parameter changes post-irradiation for neutron irradiation. Results indicate that incorporating barite as an aggregate significantly enhances the density and crystallite macroscopic properties of the concrete. Irradiation with Cobalt-60 and Cesium 137 revealed that ordinary concrete has a lower linear attenuation (μ) ranging from 0.172 to 0.195 cm−1, with consistent mass attenuation across all grades at 0.81 cm2/g. XRD analysis demonstrated a rightward shift in the SiO₂ and BaSO₄ peaks post-irradiation, signifying crystalline expansion. In terms of lattice parameters, the d-value showed a notable decrease of 0.10 after 48 h of irradiation in grade 25, while the most significant increase of 0.02 occurred after 24 h of irradiation in grades 15 and 45. In conclusion, barite concrete proves to be more effective for radiation shielding in nuclear facilities, whereas ordinary concrete is suitable for medical shielding, or facilities exposed to lower radiation doses.

Detection of extended gamma-ray emission in the vicinity of Cl Danks 1 and 2

Abstract We report the detection of high-energy gamma-ray emission towards the G305 star-forming region. Using almost 15 years of observation data from Fermi Large Area Telescope, we detected an extended gamma-ray source in this region with a significance of ∼13σ. The gamma-ray radiation reveals a clear pion-bump feature and can be fitted with the power law parent proton spectrum with an index of −2.5. The total cosmic ray (CR) proton energy in the gamma-ray production region is estimated to be the order of $10^{49}\ \rm erg$. We further derived the CR radial distribution from both the gamma-ray emission and gas distribution and found it roughly obeys the 1/r type profile, though a constant profile is not ruled out. This is consistent with other similar systems and expected from the continuous injection of CRs by the central powerful young massive star cluster Danks 1 or Danks 2 in this region. Together with former detections of similar gamma-ray structures, such as Cygnus cocoon, Westerlund 1, Westerlund 2, NGC 3603, and W40, the detection supports the hypothesis that young massive star clusters are CR accelerators.

Advancing gamma radiation shielding with Bitumen-WO₃ composite materials

This research focuses on a manner in which bitumen-WO₃ (petroleum-derived bitumen mixed with tungsten trioxide nanoparticles) materials can be a good shielding candidate against gamma radiation. The objective we set in mixing WO₃ nanoparticles with bitumen was to take advantage of both the bitumen's natural qualities and the WO₃'s excellent shielding capabilities. The prepared composites were tested against various gamma-ray energies emitted from multiple gamma-ray sources to examine their shielding capabilities. The X-ray diffraction (XRD) analysis of the composites' structural properties verified the effective integration of the WO₃ with the bitumen structure. Scanning electron microscopy (SEM) showed that microstructural changes, such as an increase in material density and an improvement in particle dispersion, are caused by a rise in WO3 concentration, which is an essential step toward efficient shielding. Then, the Mean Free Path (MFP), Half-value Layer (HVL), and Linear Attenuation Coefficients (μl) were computed, showing that the composite's capacity to reduce gamma radiation is much enhanced by raising the WO₃ content, especially at lower gamma-ray energies. For instance, at 20 keV, the LAC of 50 wt% WO₃-bitumen composite increased to 9.18 cm⁻1 compared to pure bitumen's 0.40 cm⁻1, while the HVL decreased from 1.73 cm to 0.08 cm, and the MFP dropped from 2.3 cm to 0.1 cm” The results demonstrate the potential of bitumen-WO₃ composites as a sustainable and efficient material for radiation shielding, particularly highlighting their applicability in various sectors, including the development of building wall paints against gamma radiation.

Intensive γ -ray light sources based on oriented single crystals

The feasibility of gamma-ray light sources based on the channeling phenomenon of ultrarelativistic electrons and positrons in oriented single crystals is demonstrated using rigorous numerical modeling. Case studies are presented for 10 GeV and sub-GeV e−/e+ beams incident on 10−1−100 mm thick diamond and silicon crystals. It is shown that for moderate values of the beam average current (≲10 μA), the average photon flux in the energy range of 100–102 MeV emitted within the 101–103 μrad cone and 1% bandwidth can be on the level of 1010 photon/s for electrons and 1010–1012 photon/s for positrons. These values are higher than the fluxes available at modern laser-Compton gamma-ray light sources. Published by the American Physical Society 2024

Ultra-high-energy gamma-ray bubble around microquasar V4641 Sgr.

Microquasars are laboratories for the study of jets of relativistic particles produced by accretion onto a spinning black hole. Microquasars are near enough to allow detailed imaging of spatial features across the multiwavelength spectrum. The recent extension measurement of the spatial morphology of a microquasar, SS 433, to TeV gamma rays1 localizes the acceleration of electrons at shocks in the jet far from the black hole2. V4641 Sagittarii (V4641 Sgr) is a similar binary system with a black hole and B-type main-sequence companion star and has an orbit period of 2.8 days (refs. 3,4). It stands out for its super-Eddington accretion5 and for its radio jet, which is one of the fastest superluminal jets in the Milky Way. Previous observations of V4641 Sgr did not report gamma-ray emission6. Here we report TeV gamma-ray emission from V4641 Sgr that reveals particle acceleration at similar distances from the black hole as SS 433. Furthermore, the gamma-ray spectrum of V4641 Sgr is among the hardest TeV spectra observed from any known gamma-ray source and is detected above 200 TeV. Gamma rays are produced by particles, either electrons or protons, of higher energies. Because energetic electrons lose energy more quickly the higher their energy, such a spectrum either very strongly constrains the electron-production mechanism or points to the acceleration of high-energy protons. This suggests that large-scale jets from microquasars could be more common than previously expected and that they could be a notable source of galactic cosmic rays7-9.

A study on in-situ characterization technology development for clearance verification of radioactive waste from nuclear decommissioning

Although the clearance level of every radioactive nuclide was published by the IAEA to promote the recycling and reuse of decontaminated radioactive waste worldwide, technical and regulatory issues have always been raised around the application of the criteria. Therefore, several countries are developing in-situ characterization equipment or apparatus for on-site verification to check if the clearance criteria is met.In this study authors developed a pilot radiation detection and measurement system using in-situ characterization technology to solve the issues, which consists of a 3D scanning camera system and a built-in Monte Carlo simulation program. Measurement results show that MDA (Minimum Detectable Activity) of the current design was indisputably below the clearance level and built-in Monte Carlo simulation package closely predicts the measurements results with the error of less than 5%. This implicates that it can determine with enough margin whether the radioactivity level of decontaminated metallic components meets the clearance criteria at decommissioning site or not.Practically when we measure the radioactivity from gamma ray source mass attenuation always takes place during the photon transports through the medium. In fact, the reduction depends on the material, shapes, and radioactive sources. In this study the reduction factors were experimentally examined according to the influencing parameters and the results were saved as DCF (Density Correction Factor) in the data base. As expected, it turned out that the factor is somewhat affected by medium material and radioactive sources, but it is basically proportional to the distance of gamma ray passage.It is expected that upgraded design with more accurate and reliable instruments can make it easier for regulators to accept the application of the in-situ characterization technology on-site.

Full inverse Compton Scattering: Total transfer of energy and momentum from electrons to photons

In this article we discuss a peculiar regime of Compton Scattering that assures the maximum transfer of energy and momentum from free electrons propagating in vacuum to the scattered photons. We name this regime Full Inverse Compton Scattering (FICS) because it is characterized by the maximum and full energy loss of the electrons in collision with photons: up to 100% of the electron kinetic energy is indeed transferred to the photon. In the case of relativistic electrons, characterized by a large Lorentz factor (γ≫1), FICS regime corresponds to an incident photon energy equal to mec22, i.e. approximately 255.5 keV. We interpret such an astonishing result as FICS being the time reversal of direct Compton Scattering of very energetic photons (of energy much greater than mec2) onto atomic electrons. Although the cross section of Compton scattering is decreasing with the energy of the incident photon, making the process less probable with respect to other reactions (pair production, nuclear reactions, etc.) when high energetic photons are bombarding a target, the kinematics straightforwardly implies that the back-scattered photons would have an energy reaching asymptotically mec22. FICS is instead the unique suitable working point in Compton scattering for achieving the total transfer of (kinetic) energy exactly from the electron to the photon. Experiencing transitions from the initial momentum to zero in the laboratory system, in FICS the electron is also subject to very large negative acceleration; this fact can lead to possible experiments of sensing the Unruh temperature and related photon bath. On the other side of the energy dynamic range, low relativistic electrons can be completely stopped by moderate energy photons (tens of keV), leading to full exchange of temperature between electron clouds and photon baths. Cosmic gamma ray sources can be affected in their evolution by this peculiar FICS regime of Compton scattering.

Design and test of an X -band constant gradient structure

A light source project named very compact inverse Compton scattering gamma-ray source (VIGAS) is under development at Tsinghua University. VIGAS aims to generate monochromatic high-energy gamma rays by colliding 350-MeV electron beams with 400-nm laser photons within a 12-m beamline. To produce a high-energy electron beam in such a compact space, the system consists of an S-band high-brightness injector and six X-band high-gradient accelerating structures. The goal of the X-band structure is to operate at a high gradient of 80 MV/m. Therefore, we adopts the constant gradient traveling wave approach, where the iris from the first cell to the end cell is tapered. The structure has 72 cells, including 70 cells and 2 couplers, so we named it XT72. The frequency of XT72 is selected to 11.424 GHz, and the 2π/3 mode is adopted. In this paper, we present a comprehensive study covering the detailed design, fabrication, rf tuning, and high-power test results of the first XT72. Additionally, we compare the performance of this structure to that of the previous constant impedance structure. Our results demonstrate that the XT72 is capable of operating at an 80−MV/m gradient with a lower breakdown rate. This advancement paves the way for the development of VIGAS project and contributes to the wider application of X-band room-temperature high-gradient structures in compact accelerator facilities. Published by the American Physical Society 2024

Simulation Study on Attosecond Inverse Compton Scattering Source from Laser Wakefield Acceleration with Near-Threshold Ionization Injection

We present the generation of attosecond gamma rays via inverse Compton scattering within the framework of laser wakefield acceleration through 2D Particle-In-Cell simulations. Utilizing the near-threshold ionization injection mechanism, an attosecond micro-bunched electron beam characterized by a comb-like current density profile can be achieved with a linearly polarized laser at an intensity of a0 = 1.5. The micro-bunched beam provides a beam energy of approximately 300 MeV and achieves a minimum relative energy spread of about 1.64% after undergoing 2 mm of acceleration. In the inverse Compton scattering scheme, these attosecond electron micro-bunches interact with the reflected driving laser pulse, resulting in the attosecond gamma-ray radiation exhibiting similar structures. Individual spatial-separated gamma-ray pulses exhibit a length of approximately 260–300 as, with a critical energy of 2.0 ± 0.2 MeV. The separated attosecond gamma-ray source owns a peak brilliance of ~1022 photons s−1 mm−2 mrad−2 0.1% BW. This brilliance is competitive in a laboratory for multi-MeV γ-ray sources with a laser intensity of I = 5 × 1018 W/cm2. Such attosecond gamma-ray radiation offers promising applications requiring ultrashort X-ray/gamma ray sources.

Enhanced formula-based method to estimate burnup, initial enrichment, and cooling time using limited gamma-ray source data of reference PWR spent nuclear fuel assemblies

This study proposes a framework to develop a model for estimating burnup (BU), initial enrichment (IE), and cooling time (CT) of spent nuclear fuel (SNF) overcoming the limitations of existing models in determining IE. Database (DB) of gamma-ray sources for PWR SNF was generated using ORIGAMI. Target gamma radionuclides were selected based on the ease and credibility of measurement. The concept of Product of Powers of Radioactivity (PPR) was suggested, and PPRs for modeling were selected through evaluation of all possible PPRs. Functions established for PPRs were applied to estimate BU, IE, and CT (BIC) of PWR SNF assemblies. Optimized PPR combinations for estimating BU, IE, and CT respectively, as well as three variables simultaneously with the highest accuracy, were suggested. The estimation model proposed in this study enhanced IE estimations, maintaining the reliability of BU and CT estimations. The above framework enables construction of intuitive BIC estimation models using only a small amount of data. This can help hasten the development of estimation models for SNF from various reactor types. Consequently, it is expected to contribute to the safety and safeguards of SNF management by improving the verification that SNF meets acceptance criteria and conforms to the declared information.

On the Correlation between Young Massive Star Clusters and Gamma-Ray Unassociated Sources

Star clusters (SCs) are potential cosmic-ray accelerators and therefore are expected to emit high-energy radiation. However, a clear detection of gamma-ray emission from this source class has only been possible for a handful of cases. This could in principle result from two different reasons: either detectable SCs are limited to a small fraction of the total number of Galactic SCs, or gamma-ray-emitting SCs are not recognized as such and therefore are listed in the ensemble of unidentified sources. In this Letter we investigate this latter scenario by comparing available catalogs of SCs and H ii regions, obtained from Gaia and Wide-field Infrared Survey Explorer observations, to the gamma-ray GeV and TeV catalogs built from Fermi Large Area Telescope (LAT), H.E.S.S., and LHAASO data. The significance of the correlation between catalogs is evaluated by comparing the results with simulations of synthetic populations. A strong correlation emerges between Fermi-LAT-unidentified sources and H ii regions that trace massive SCs in the earliest (≲1–2 Myr) phase of their life, where no supernova explosions have happened yet, confirming that winds of massive stars can alone accelerate particles and produce gamma-ray emission at least up to GeV energies. The association with TeV energy sources is less evident. Similarly, no significant association is found between Gaia SCs and GeV nor TeV sources. We ascribe this fact to the larger extension of these objects but also to an intrinsic bias in the Gaia selection toward SCs surrounded by a lower target gas density, which would otherwise hinder the detection in the optical wave band.

A single-layer compton camera for nuclear decommissioning: An improved back-projection algorithm

The decommissioning of nuclear facilities, a critical and hazardous process due to radiation exposure, necessitates the advancement of radiological measurement techniques concerning safety and efficiency. This study presents an optimized back-projection method, integrating a novel single-layer Compton camera and 3D camera setup with the Timepix3 readout chip to improve the precision and efficiency of gamma-ray source localization in decommissioning scenarios. Implementing ‘twin addition’ and ‘twin multiplication’ techniques addressed data ambiguities that arise from event selection in the Compton camera, enhancing the reliability of localization. Introducing a zoom function significantly improved computational efficiency, achieving 163 times faster computation times without sacrificing accuracy. Our method demonstrated enhanced precision with a median angular error of 1.41°, outperforming traditional methods and showing competitive advantages over state-of-the-art technologies, including the Caliste-HD detector. The feasibility of integrating this methodology onto mobile robotic platforms suggests a promising avenue to minimize human radiation exposure and optimize decommissioning tasks, ensuring safer and more effective nuclear facility decommissioning.

Detection prospects of very and ultra high-energy gamma rays from extended sources with ASTRI, CTA, and LHAASO

Context. The recent discovery of several ultra high-energy gamma-ray emitters in our Galaxy represents a significant advancement towards the characterisation of its most powerful accelerators. Nonetheless, in order to unambiguously locate the regions where the highest energy particles are produced and understand the responsible physical mechanisms, detailed spectral and morphological studies are required, especially given that most of the observed sources were found to be significantly extended. Aims. In these regards, pointing observations with the next-generation Imaging Atmospheric Cherenkov Telescopes, such as the Cherenkov Telescope Array (CTA) Observatory and the ASTRI Mini-Array (ASTRI), are expected to provide significant improvements. Here we aim to identify the most promising sources to target in future observations. Methods. For this purpose, we performed a comparative analysis of the expected performance of ASTRI and CTA, computing their differential sensitivities towards extended sources, and further explored their capabilities with respect to specific case studies, including follow-ups of existing gamma-ray source catalogues. Results. We find that almost all of the sources thus far detected by LHAASO-WCDA and in the H.E.S.S. Galactic Plane Survey will be in the reach of ASTRI and CTA with about 300 and 50 hours of exposure, respectively. For the highest energy emitters detected by LHAASO-KM2A, in turn, we provide a list of the most promising objects that would require further investigation. We additionally examined specific classes of sources in order to identify potentially detectable gamma-ray emitters, such as passive molecular clouds (i.e. illuminated by the cosmic-ray sea) and pulsars surrounded by a halo of runaway particles.

Fabrication and high-power testing of an X-band high-power phase shifter for the very compact inverse Compton scattering gamma-ray source.

This paper proposed an X-band phase shifter for the very compact inverse Compton scattering gamma-ray source program at Tsinghua University and conducted its structure design, numerical simulation, fabrication, cold test, and high-power testing. This phase shifter is composed of a polarizer, circular waveguide, and a piston with a choke structure. The simulation results show that the reflection coefficient of the phase shifter is under -40 dB and the insertion coefficient exceeds -0.06 dB at the operating frequency of 11.424GHz. The phase variation is 20°/mm, and a linear phase change from 0° to 360° can be achieved with a piston displacement of 18mm. The manufactured phase shifter has exhibited good performance in the cold test by using the vector network analyzer. After 16h conditioning in the Tsinghua X-band high-power test stand, the phase shifter reached a peak power of 72MW at 230ns pulse width and a peak power of 82MW at 130ns pulse width. After processing signals from the high-speed oscilloscope, it was found that the transmission phase variations were in good agreement with the simulation results.

Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC

We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ( dN/dE=ϕE/26TeVγ ), where γ = −2.88 ± 0.15stat − 0.1sys and ϕ = 1.5 × 10−15 (TeV cm2 s)−1 ±0.3stat−0.13sys+0.08sys extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (>5σ), with the spectrum extending to >100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC.