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The research aims to study the primary interaction between gamma radiation in CeBr3 crystal. The analysis of mass attenuation coefficient (MAC), effective atomic number (Zeff), electron density (Neff), mean free path (MFP), and energy absorption buildup factor (EABF) was evaluated using the using the WinXCom software. Also, the interaction with charged particles as the total mass stopping power (TMSP), projected range (PR) of proton ( H 1 1 ) and alpha ( H 2 4 e ) particles were evaluated by SRIM programming. The results found that the MAC depends on the energy ranges, the photoelectric effect is the main interaction at low energy ranges, Compton scattering phenomena illustrate and evidents at intermediate energy ranges, and pair production characteristics dominate over on 1.022 MeV in high energy ranges. Moreover, absorption edges appear on energy's discontinuity at low energy. The Zeff and Neff show similar trends and correspond to the energy ranges. The MFP of the CeBr3 compared with some standard scintillators such as NaI and BGO crystal and found that the BGO responds to faster interaction than CeBr3 and NaI crystals. The EABF shows scattering energies followed by atomic equivalent (Zeq), and they also increase with increasing penetration depth (mfp). The TMSP and PR depend on charged particles, density, and the unit path distance of a material. [ABSTRACT FROM AUTHOR]

The use of neutron activation analysis (NAA) sometimes has limitations with the identification of specific gamma ray peaks due to spectral interferences. The implementation of gamma-gamma coincidence techniques using the XIA Pixie-16 system has demonstrated the ability reduce many of these challenges. Experiments were performed on two different NIST reference materials using gamma-gamma coincidence techniques to identify long-lived radionuclides that are often difficult to evaluate due to various spectral interferences. The experiments have shown that utilizing gamma-gamma coincidence with the XIA Pixie-16 system for 177mLu, 124Sb, 160 Tb, 175Yb, and 153Sm can eliminate spectral interferences and high backgrounds due to Compton scattering. [ABSTRACT FROM AUTHOR]

Diverse phenomena such as positron annihilation in the Milky Way, merging binary neutron stars, and dark matter can be better understood by studying their gamma ray emission. Despite their importance, MeV gamma rays have been poorly explored at sensitivities that would allow for deeper insight into the nature of the gamma emitting objects. In response, a liquid argon time projection chamber (TPC) gamma ray instrument concept called GammaTPC has been proposed and promises exploration of the entire sky with a large field of view, large effective area, and high polarization sensitivity. Optimizing the pointing capability of this instrument is crucial and can be accomplished by leveraging convolutional neural networks to reconstruct electron recoil paths from Compton scattering events within the detector. In this investigation, we develop a machine learning model architecture to accommodate a large data set of high fidelity simulated electron tracks and reconstruct paths. We create two model architectures: one to predict the electron recoil track origin and one for the initial scattering direction. We find that these models predict the true origin and direction with extremely high accuracy, thereby optimizing the observatory's estimates of the sky location of gamma ray sources. [ABSTRACT FROM AUTHOR]

In positron annihilation, exploration of the polarization correlations of the emerging gamma quanta has gained interest, since they offer a possibility to improve signal-to-background in medical imaging using positron emission tomography. The annihilation quanta, which are predicted to be in an entangled state, have orthogonal polarizations and this property may be exploited to discriminate them from two uncorrelated gamma photons contributing to the background. Recent experimental studies of polarization correlations of the annihilation quanta after a prior Compton scattering of one of them, had rather different conclusions regarding the strength of the correlation after the scattering, showing its puzzling nature. The scattering was described as a decoherence process. In the present work, we perform for the first time, a study of the polarization correlations of annihilation quanta after decoherence via Compton scattering in the angular range 0 ∘ − 50 ∘ using single-layer gamma ray polarimeters. In addition, we compare the measured polarization correlations after Compton scattering at 30 ∘ with an active and a passive scatterer element. The measured azimuthal correlation of back-to-back annihilation quanta is consistent with the Pryce-Ward formulation, as confirmed by Monte Carlo simulations. Further, the results indicate that the correlation, expressed in terms of the polarimetric modulation factor, shows no significant difference at small scattering angles (0 ∘ − 30 ∘) compared to the correlation measured for direct photons, while a moderate indication of a lower modulation is observed for 50 ∘ scattering angle. The measured modulation is larger at all scattering angles than the one expected from the simulation of orthogonally polarized, independent annihilation quanta. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of borate-based glasses doped with BaO, assessing their physical, structural, optical, and radiation shielding properties through experimental and theoretical analyses. XRD patterns reveal the amorphous nature of the prepared glass samples. Density and molar volume values, and FTIR spectra indicate the impact of BaO concentration on the glass matrix, affecting structural properties. Thermal analysis via TGA/DSC reveals improved thermal properties with the substitution of B 2 O 3 with BaO. UV–visible absorption spectroscopy shows a decrease in energy band gap with rising BaO content, suggesting potential non-bridging oxygen formation. Mass attenuation coefficient (μ m) values exhibit an exponential decay trend with photon energy, influenced by photoelectric absorption, Compton scattering, and pair creation. The glasses prepared had, in general, a better μ m values compared to that of concretes and other glass compositions containing barium oxide. Experimental and theoretical (XCOM) results for mean free path (MFP) and half-value layer (HVL) demonstrate close agreement, validating the accuracy of the experimental data. Both MFP and HVL increase with energy and decrease with BaO addition, emphasizing the potential for these glasses in radiation shielding applications. • Borate based glass samples of the composition (70-x)B 2 O 3 –20Bi 2 O 3 –5ZnO–5WO 3 -xBaO; x = 0, 5, 10, 15 and 20 mol% have been successfully prepared by melt-quenching process. • The addition of BaO in the glass system improves its density, thermal and gamma radiation shielding properties. • The study elucidates structural modifications of borate glasses imparted by the doping of BaO. • Non-toxic and environmentally friendly nature, along with effective shielding behavior, of our prepared glass samples makes it a practical solution for gamma shielding applications. [ABSTRACT FROM AUTHOR]

Obtaining directional information is required in many applications such as nuclear homeland security, contamination mapping after a nuclear incident and radiological events, or during the decontamination work. However, many directional radiation detectors are based on directional shielding, made of lead or tungsten collimators, introducing two main drawbacks. The first is the size and weight, making those detectors too heavy and irrelevant for utilization in handheld devices, drone mapping, or space applications. The second drawback is the limited field of view (FOV), which requires multiple detectors to cover the whole required FOV or machinery to rotate the detector’s narrow FOV detector. We propose a novel $4\pi $ directional detector based on a segmented hollow cubic detector, which uses the Compton effect interactions with no heavy collimators. The symmetrical cubical design provides both higher efficiency and $4\pi $ detection ability. Instead of the traditional two types of detectors (scatterer and absorber) structure, we use the same type of detector, based on Gd3Al2Ga3O12 (GAGG) (Ce) scintillator coupled to silicon photomultiplier. An additional advantage of the proposed detector is obtained by locating the photon sensors inside the detector, behind the scintillators, which improves the radiation hardness required for space applications. Furthermore, such an arrangement flattens the temperature variation across the detector, providing better gain stability. The main advantage of the proposed detector is an efficient $4\pi $ radiation detection for high-energy gamma rays without the use of heavy collimators. [ABSTRACT FROM AUTHOR]

In this study, albedo parameters are experimentally measured to determine radiation scattering features of some thermoluminescent dosimetry materials (TLD 100, TLD 100h, TLD 200 and TLD 400). In experimental setup, it was used scattering angle of 168°, 59.54 keV gamma rays and HPGe detector. The effective atomic numbers of the investigated materials were determined from the coherent to Compton scattering intensity ratio. Also, the mass attenuation coefficient, the mass energy absorption coefficient and kerma relative to air and ICRU tissue were calculated for the TLD materials. It was observed that TLD 100h is the best tissue equivalent material among other TLD materials and best reflects 59.54 keV gamma rays. • The effective atomic numbers of some thermoluminescent dosimetry materials were obtained from scattering ratios. • The effective atomic number and albedo parameters are obtained for 59.54 keV photon energy. • TLD 100h is the material that best reflects 59.54 keV gamma rays. [ABSTRACT FROM AUTHOR]

The gamma-radiation shielding capabilities of a Ni 0.2 Mg x Zn 0.8-x Fe 2 O 4 nanocrystal, synthesized using the sol-gel auto-ignition process, were described in the present investigation. The synthesized materials were analyzed using different techniques such as XRD, UV–Vis, FTIR, FE-SEM, and EDS to investigate their structural, optical, and functional group morphological properties, and elemental analysis. Additionally, utilizing various gamma-ray sources and a NaI (Tl) scintillation detector, we investigated the gamma-ray shielding parameters for the prepared materials. The cubic spinel structure of all produced Nanoferrites is clear from X-ray diffractograms, which show no contaminated phases. Pellets of nanocrystalline spinel ferrites have been exposed to gamma radiation from various sources by varying the intensity of the radiation dose. Utilizing Phy-X/PSD Software, a comparative analysis of the mass and linear attenuation coefficients, mean free path, half value layer, tenth value layer, effective atomic number, and effective electron density for synthesized spinel ferrites is performed at 122–1330 keV. Using the geometric progression (G-P) fitting technique, the gamma-ray energy absorption build-up factor (EABF) for four selected ferrites is explored at incident photon energy levels ranging from 0.015 to 15 MeV. It is found that the Compton scattering process is mostly responsible for the EABF maximum in an intermediate region. K1 has a higher EABF value than other ferrites, which is largely determined by the crystallite size effect and the chemical composition of the material. There is a good agreement between the theoretical and experimental results. Among the studied samples, sample K1 and K4 have superior gamma-ray and fast neutron attenuation capabilities respectively than its counterparts. The current study offers a thorough examination of the chosen iron oxides in the context of gamma and neutron radiation. • The values of μ m , μ, Z eff , λ, HVL, TVL were determined experimentally using NaI (Tl) detector. • Experimental results have been supported with Phy-X/PSD Software values. • The energy absorption buildup factor have been calculated using G.P. fitting method. • The values of macroscopic removal cross-sections for neutrons were determined. • Measured data in mixed neutron-gamma radiation field are useful in nuclear medicine application. [ABSTRACT FROM AUTHOR]

The production, application, and/or measurement of polarised X-/gamma rays are key to the fields of synchrotron science and X-/gamma-ray astronomy. The design, development and optimisation of experimental equipment utilised in these fields typically relies on the use of Monte Carlo radiation transport modelling toolkits such as Geant4. In this work the Geant4 "G4LowEPPhysics" electromagnetic physics constructor has been reconfigured to offer a best set of electromagnetic physics models for studies exploring the transport of low energy polarised X-/gamma rays. An overview of the physics models implemented in "G4LowEPPhysics", and it's experimental validation against Compton X-ray polarimetry measurements of the BL38B1 beamline at the SPring-8 synchrotron (Sayo, Japan) is reported. "G4LowEPPhysics" is shown to be able to reproduce the experimental results obtained at the BL38B1 beamline (SPring-8) to within a level of accuracy on the same order as Geant4's X-/gamma ray interaction cross-sectional data uncertainty (approximately ± 5 %). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper analyzes the intrinsic energy resolution, the influence law of multiple Coulomb scattering, the radiation conversion efficiency, and other factors of the Compton radiation conversion target. Based on the essential principle of interaction between gamma rays and matter, the theoretical characteristics and transport law of Compton electrons are analyzed. Through a Monte Carlo simulation, the composition, energy, and angular distribution of electrons emitted from the target surface are calculated; the influence of target parameters, such as target material, thickness, and electron collection angle, on target performance is studied; and then the optimization method of target parameters is established. Finally, the main performance parameters of the Compton radiation conversion target are given. This research reveals how multiple Coulomb scattering angles relate to materials of different types and thicknesses, as well as to the optimal collection angle. A series of optimized parameters for the material, mass thickness, and corresponding energy resolution of radiation conversion target with different conversion efficiencies are obtained. [ABSTRACT FROM AUTHOR]

The influence of sample thickness to the background region in energy dispersive x-ray fluorescence (EDXRF) system was investigated. The investigated spectrum was from 4.09 keV to 79.03 keV and was divided into 8 regions. Some of these regions include contributions by photons from tails of fluorescent lines. HgO samples with thicknesses from 0.010 to 0.335 cm were prepared. The samples were excited by 59.54 keV gamma rays from a 5 Ci Am241 annular radioactive source in an energy dispersive x-ray fluorescence system. The scattered and emitted photons were counted by a high purity germanium (HPGe) detector. The results showed that the background intensity increases with the sample thickness and further enhancement in results in no further increase in the background intensity. The determined saturation (experimental) and critical (theoretical) thickness values considering the low and high energy tail regions of Compton scattering peak were compatible. [ABSTRACT FROM AUTHOR]

A compact broadband Compton spectrometer is designed to measure the continuous spectrum of gamma-ray sources driven by an intense laser. The incident gamma rays are converted into electrons in low-Z materials by Compton scattering. Produced by a pair of stepped magnets, a weaker-front–stronger-rear nonuniform magnetic field in the electron magnetic spectrometer is used to spectrally resolve the scattered electrons, leading to a broadband gamma-ray spectral coverage of 2–20 MeV in a compact volume. Flat imaging-plate detectors are placed near the focused imaging points of the magnetic spectrometer to record the dispersed electrons, thereby achieving an optimal spectral resolution of 6%–13% in the energy range of 3–20 MeV. The spectrometer is used successfully to measure the gamma-ray spectrum generated by the high-energy electron beams produced by a femtosecond-laser-driven wakefield. [ABSTRACT FROM AUTHOR]

To detect gamma rays with good spatial, timing and energy resolution while maintaining high sensitivity we need accurate and efficient algorithms to estimate the first gamma interaction position from the measured light distribution. Furthermore, monolithic detectors are investigated as an alternative to pixelated detectors due to increased sensitivity, resolution and intrinsic DOI encoding. Monolithic detectors, however, are challenging because of complicated calibration setups and edge effects. In this work, we evaluate the use of neural networks to estimate the 3D first (Compton or photoelectric) interaction position. Using optical simulation data of a 50 × 50 × 16 mm3 LYSO crystal, performance is evaluated as a function of network complexity (two to five hidden layers with 64 to 1024 neurons) and amount of training data (1000−8000 training events per calibration position). We identify and address the potential pitfall of overfitting on the training grid through evaluation on intermediate positions that are not in the training set. Additionally, the performance of neural networks is directly compared with nearest neighbour positioning. Optimal performance was achieved with a network containing three hidden layers of 256 neurons trained on 1000 events/position. For more complex networks, the performance degrades at intermediate positions and overfitting starts to occur. A median 3D positioning error of 0.77 mm and a 2D FWHM of 0.46 mm is obtained. This is a 17% improvement in terms of FWHM compared to the nearest neighbour algorithm. Evaluation only on events that are not Compton scattered results in a 3D positioning error of 0.40 mm and 2D FWHM of 0.42 mm. This reveals that Compton scatter results in a considerable increase of 93% in positioning error. This study demonstrates that very good spatial resolutions can be achieved with neural networks, superior to nearest neighbour positioning. However, potential overfitting on the training grid should be carefully evaluated. [ABSTRACT FROM AUTHOR]

This work investigates the electronic momentum density (EMD) distribution in nanosize zirconia (ZrO2) using the technique of Compton scattering. The ZrO2 nanoparticles (11.2 nm) are synthesized of mechanical milling and characterized by SEM, XRD and TEM probes. The Compton profile J (p z) of nanoZrO2 is measured by Compton spectrometer 59.54 KeV Gamma rays (Americium-241) source. The study finds out that EMD in nanoZrO2 is narrower comparing in case bulk ZrO2. This study adopts the ionic-model-based free atom J (p z) calculation for many configurations (Zr) + x (O − x ∕ 2 )2 (0. 0 ≤ x ≤ 0. 2) to measure the charge transfer (CT) on the compound formation. According to this study's findings, CT values in these materials are ranged from 1.5 to 1.0 electrons from Zr to O atom. [ABSTRACT FROM AUTHOR]

Radiation is used in many applications such as medicine, therapy, industry but it also has some disadvantages or hazards. Therefore, the knowledge of how radiation interacts with matter becomes very important at different photon energies. In the present study, Compton mass attenuation coefficients of different types of materials were investigated via Klein-Nishina formula in the energy range 0.284–15 MeV. Different methods were used to determine Compton mass attenuation coefficients of the materials. The results were compared with each other in terms of the methods. According to the results, Klein-Nishina electronic cross-sections and Compton mass attenuation coefficients of the studied materials were decreased with increasing γ-ray energy like the elements. In addition, the results were compared with possible results from literature as the mean result of the study. A good agreement was observed for Zn, Sn, Te, Ba, W and Bi elements (Diff. ≤ 6.25%) at 1.173 MeV photon energy. Best agreement was also observed for ZnS and CaCO 3 compounds (0.14% ≤ Diff. ≤ 22.18%) at 4 and 1.332 MeV photon energies respectively. The reported data should be useful when the gamma rays into these materials especially in Compton scattering energy region. • CMACs of important materials were determined using Klein-Nishina theory. • Different methods were used to calculate CMACs. • The methods were especially performed at Compton scattering energy region. [ABSTRACT FROM AUTHOR]

With the rapid development of inverse Compton scattering gamma-ray sources, highly polarized gamma rays play a significant role in fundamental nuclear physics research based on nuclear resonance fluorescence (NRF). To meet the requirements of those applications, especially for guiding experiments and optimizing detection systems, a Monte Carlo simulation method for linearly polarized gamma-ray NRF is developed and implemented in the general-purpose toolkit Geant4. To validate the effectiveness of this method, simulations are compared with both theoretical and experimental results and are found to agree well with both. As a typical application of the linearly polarized gamma-ray NRF technique, a gamma-ray polarization measurement method is proposed in the energy region from hundreds of keV to several MeV, and its feasibility is analyzed based on the developed simulation method. Compared with the conventional Compton scattering method, the analyzing power of the NRF method is improved about 3.7-fold by using a 28 Si target, and reaches a value of more than 0.99 at a reasonable data acquisition time. [ABSTRACT FROM AUTHOR]

Gamma-ray continuum at > 10 MeV photon energy yields information on ≳ 0.2 – 0.3 GeV/nucleon ions at the Sun. We use the general-purpose Monte Carlo code FLUktuierenden KAskade (FLUKA) to model the transport of ions injected into thick and thin target sources, the nuclear processes that give rise to pions and other secondaries and the escape of the resulting photons from the atmosphere. We give examples of photon spectra calculated with a range of different assumptions about the primary ion velocity distribution and the source region. We show that FLUKA gives results for pion decay photon emissivity in agreement with previous treatments. Through the directionality of secondary products, as well as Compton scattering and pair production of photons prior to escaping the Sun, the predicted spectrum depends significantly on the viewing angle. Details of the photon spectrum in the ≈ 100 MeV range may constrain the angular distribution of primary ions and the depths at which they interact. We display a set of thick-target spectra produced making various assumptions about the incident ion energy and angular distribution and the viewing angle. If ions are very strongly beamed downward, or ion energies do not extend much above 1 GeV/nucleon, the photon spectrum is highly insensitive to details of the ion distribution. Under the simplest assumptions, flares observed near disc centre should not display significant radiation above 1 GeV photon energy. We give an example application to Fermi Large Area Telescope data from the flare of 12 June 2010. [ABSTRACT FROM AUTHOR]

Radiation portal monitors are commonly used to detect and intercept unauthorized movement of nuclear and other radioactive materials at country borders. A total of twelve double- pillar portal monitors are present at the Greek-North Macedonian border, each containing two polystyrene scintillating detectors per pillar. Spatial and spectral response testing of the scintillating detectors to gamma radiation was performed by using different radioactive sources and comparing the measurement results with Monte Carlo simulations. A good agreement of the experimentally deduced activities of different point sources, needed for alarm triggering of the radiation portal monitors with Monte Carlo calculated values, was observed. Spectral results show no photopeaks in the spectra due to low resolution of these detectors. The broad peaks observed in the spectra correspond to the Compton edge. Measured spectra with a 137Cs source placed directly on the scintillating detector, at several positions away from the photo multiplier tube, show an energy shift of the Compton edge towards lower energies, as the source is moving away from the photo multiplier tube. The energy shift is due to light transfer mechanisms within the scintillator volume and therefore, it is only observed in optical simulations and not in gamma-ray particle simulations. [ABSTRACT FROM AUTHOR]

The isotope selectivity of computed tomography (CT) imaging based on nuclear resonance fluorescence (NRF) transmission method using a quasi-monochromatic laser Compton scattering (LCS) gamma-ray beam in the MeV region was demonstrated at the Ultra Violet Synchrotron Orbital Radiation–III (UVSOR-III) Synchrotron Radiation Facility (Institute of Molecular Science, National Institute of Natural Science) for two enriched lead isotope rods (206Pb and 208Pb) implanted in an aluminum cylinder. Since these two rods show the same gamma-ray attenuation in atomic processes, it is impossible to differentiate between them using a standard Gamma-CT technique based on atomic attenuation of gamma rays. The LCS gamma-ray beam had a maximum energy of 5.528 MeV and an intensity of approximately 5.5 photons/s/eV at the resonance energy (Jπ = 1&$8722; at 5.512 MeV in 208Pb). A lead collimator with a hole diameter of 1 mm was used to define the size of the LCS gamma-ray beam at the CT target. The CT image of the 208Pb rod was selectively obtained with a 2-mm pixel size resolution, which was determined by the horizontal step size of the CT stage. [ABSTRACT FROM AUTHOR]

Fissionable materials can be distinguished from normal materials by their emission of fast neutrons and neutrons moderated by surrounding materials. Radioisotopes can often be identified by their gamma-ray spectra. In this work, we use the nuclear physics Monte Carlo package MCNP6.2 to compare the detection efficiencies of different detector designs for the triple-mode detection of fast and moderated neutrons, and gamma-ray spectroscopy. For each design, we tabulate the detection efficiencies for neutrons from 0.1 eV to 5 MeV and for the full absorption of gamma rays from 0.1 to 5 MeV. All designs use 100 scintillators 1 cm × 1 cm × 5 cm. Of these, 36 are Cs2 LiLaBr6:Ce (90% 6Li) (CLLB) and 64 are polyvinyl toluene (PVT). The first design uses separate arrays of 6 × 6 CLLB and 8 × 8 PVT scintillators. Three other designs are 10 ×10 composite arrays using all 100 scintillators combined in different ways. PVT is a fast scintillator that can be used to detect fast neutrons by time-separated multiple proton recoils and discriminate against gammas. PVT in the three composite designs serves to moderate neutrons of all energies for capture by the 6Li in the CLLB. Gamma rays interact in the PVT and CLLB by Compton scattering and pair production; full energy absorption requires photoelectric absorption in the CLLB. The energy deposited by each gamma ray can be determined from a weighted sum of the CLLB and PVT signals from separate photodetectors. We find that for a fixed number of neutrons/cm2, one of the composite arrays has much higher 6Li detection efficiencies than the design that uses separate CLLB and PVT arrays, and has similar detection efficiencies for fast neutrons and gammas. We also find that in all cases, the average energy of the neutrons at capture by 6Li is well above the 25-meV thermal energy. [ABSTRACT FROM AUTHOR]

M 87 is one of the closest (z  = 0.004 36) extragalactic sources emitting at very high energies (VHE, E > 100 GeV). The aim of this work is to locate the region of the VHE gamma-ray emission and to describe the observed broad-band spectral energy distribution (SED) during the low VHE gamma-ray state. The data from M 87 collected between 2012 and 2015 as part of a MAGIC monitoring programme are analysed and combined with multiwavelength data from Fermi -LAT, Chandra, HST , EVN, VLBA, and the Liverpool Telescope. The averaged VHE gamma-ray spectrum can be fitted from ∼100 GeV to ∼10 TeV with a simple power law with a photon index of (−2.41 ± 0.07), while the integral flux above 300 GeV is |$(1.44\pm 0.13)\times 10^{-12}\, \mathrm{cm}^{-2}\, \mathrm{s}^{-1}$|⁠. During the campaign between 2012 and 2015, M 87 is generally found in a low-emission state at all observed wavelengths. The VHE gamma-ray flux from the present 2012–2015M 87 campaign is consistent with a constant flux with some hint of variability (⁠|$\sim 3\, \sigma$|⁠) on a daily time-scale in 2013. The low-state gamma-ray emission likely originates from the same region as the flare-state emission. Given the broad-band SED, both a leptonic synchrotron self-Compton and a hybrid photohadronic model reproduce the available data well, even if the latter is preferred. We note, however, that the energy stored in the magnetic field in the leptonic scenario is very low, suggesting a matter-dominated emission region. [ABSTRACT FROM AUTHOR]

In this study, various detector configurations have been investigated in order to explore the optimal condition for decay rate measurements of radioactive samples using gamma spectroscopy technique. A limitation of detecting low energy gamma rays from decaying radioactive nuclei, is the Compton background which can be significantly reduced by rejecting Compton scattered events through active Bismuth germanate (BGO) shielding. On the other hand, for a CLOVER detector without BGO shielding, one can place the radioactive samples very close to the detector for enhancing geometrical efficiency. A single crystal High Purity Germanium (HPGe) detector can also be used for decay rate measurements. In order to measure the decay rate of nuclei decaying via gamma emission with reasonable intensity, optimal close geometry options have been investigated for various HPGe detector configurations. [ABSTRACT FROM AUTHOR]

The coherent to Compton differential cross section ratios were calculated for elements in the range 20 ≤ Z ≤ 32 under an external magnetic field. The elements were irradiated by 59.54 keV gamma rays from an 241Am radioactive source. A Si(Li) detector was used to detect the scattered photons. It was observed that the coherent to Compton differential cross section ratios of the samples increase with the magnetic field (B = 0, 0.4, and 0.8 T). The theoretical results were obtained with two different methods and compared with the experimental results at 0 T. [ABSTRACT FROM AUTHOR]

Relativistic jets from blazars are known to be sources of very high energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic background light (EBL) and the cosmic microwave background (CMB), producing electron–positron pairs. These pairs can upscatter CMB/EBL photons to high energies via inverse Compton (IC) scattering, thereby continuing the cascade process. This is often used to set limits on intergalactic magnetic fields (IGMFs). However, the picture may change if plasma instabilities, arising due to the interaction of the pairs with the intergalactic medium (IGM), cool down the electrons/positrons faster than inverse Compton scattering. As a consequence, the kinetic energy lost by the pairs to the IGM could cause a hardening in the observed gamma-ray spectrum at energies below ∼100 GeV. Here, we study several types and models of instabilities and assess their impact for interpreting observations of distant blazars. Our results suggest that plasma instabilities can describe the spectra of some blazars and mimic the effects of IGMFs, depending on parameters such as intrinsic spectrum of the object, the density and temperature of the IGM, and the luminosity of the beam. On the other hand, we find that for our fiducial set of parameters plasma instabilities do not have a major impact on the spectra of some of the blazars studied. Therefore, they may be used for constraining IGMFs. [ABSTRACT FROM AUTHOR]

Many PET scanner detectors use LSO or LYSO as their scintillation crystals. Since natural lutetium contains 2.6% radioactive 176Lu, which decays β− followed by the emission of three gamma rays or internal conversion electrons, its intrinsic radioactivity needs to be considered. This work compares the energy spectrum obtained with Monte Carlo simulations of ionizing radiation transport using the 176Lu ion source defined in GATE v8.1, for different LYSO crystal sizes with experimental and analytical data. In addition, we performed a set of simulations of 88, 202 and 307 keV monoenergetic photons, the gamma rays of the isomeric transitions of the 176Hf excited states, to quantify the Compton scattered photons interacting in or escaping the crystal. Even though the optical transport effects were not simulated, the results show a very good agreement with analytical and experimental data and support the accuracy for modeling the intrinsic radioactivity of LSO/LYSO crystals with GATE. [ABSTRACT FROM AUTHOR]

Previously, we proposed a novel method to inspect the isotropy of the properties of gamma-ray bursts (GRBs), such as their duration, fluences and peak fluxes at various energy bands and different time-scales, complementary to existing studies of the spatial distribution of GRBs by other authors. The method was then applied to the Fermi Gamma-ray Burst Monitor (GBM) Burst Catalog containing 1591 GRBs. Except for one particular direction where we noticed some hints of violation from statistical isotropy, the rest of the data showed consistency with isotropy. In this work, we apply our method, with some minor modifications, to the updated Fermi GBM data sample containing 2266 GRBs, which is thus ∼40  per cent larger. We also test two other major GRB catalogues: the Burst And Transient Source Experiment (BATSE) Current GRB Catalog of the Compton Gamma Ray Observatory (CGRO), containing ∼2000 bursts, and the Swift Burst Alert Telescope (BAT) GRB Catalog, containing ∼1200 bursts. The new results using the updated data are consistent with our previous findings and we find no statistically significant anisotropic feature in the observed properties of these samples of all GRBs. [ABSTRACT FROM AUTHOR]

Almost 10 yr of γ-ray observations with the Fermi Large Area Telescope have revealed extreme γ-ray outbursts from flat spectrum radio quasars (FSRQs), temporarily making these objects the brightest γ-ray emitters in the sky. Yet, the location and mechanisms of the γ-ray emission remain elusive. We characterize long-term γ-ray variability and the brightest γ-ray flares of six FSRQs. Consecutively zooming in on the brightest flares, which we identify in an objective way through Bayesian blocks and a hill-climbing algorithm, we find variability on subhour timescales and as short as minutes for two sources in our sample (3C 279 and CTA 102) and weak evidence for variability at timescales less than the Fermi satellite's orbit of 95 minutes for PKS 1510–089 and 3C 454.3. This suggests extremely compact emission regions in the jet. We do not find any signs of γ-ray absorption in the broad-line region (BLR), which indicates that γ-rays are produced at distances greater than hundreds of gravitational radii from the central black hole. This is further supported by a cross-correlation analysis between γ-ray and radio/millimeter light curves, which is consistent with γ-ray production at the same location as the millimeter core for 3C 273, CTA 102, and 3C 454.3. The inferred locations of the γ-ray production zones are still consistent with the observed decay times of the brightest flares if the decay is caused by external Compton scattering with BLR photons. However, the minute-scale variability is challenging to explain in such scenarios. [ABSTRACT FROM AUTHOR]

Due to the discrepancies of gamma-induced Displacement per Atom (DPA) cross sections among different calculations, the present work identifies the sources of the discrepancies and recommends the computation of displacement cross sections induced by photons, including the stopping power for electrons and positrons, the differential scattering cross sections, and the gamma-matter interactions. The production of electrons and positrons and the corresponding gamma-induced damage cross sections computed with the above methods are validated against Monte Carlo simulations. The damage cross section for Photoelectric Effect (PE) is negligible for incident photon energy higher than 2 MeV. Above 2 MeV, the percentage of atomic displacement for Compton Scattering (CS) decreases with incident energy, while that for Pair Production (PP) increases and becomes more important than CS above 10 MeV. In the PP, it is recommended to differently treat positrons and electrons for damage calculations because positrons produce 68–77% of DPA induced by electrons. 9.8 × 10−10 DPA/year gamma-induced displacement is obtained in the heavy reflector of PERLE experiment using the recommended damage cross sections. Neglecting the influence of moderator on photon flux in reflector, 8.1 × 10−4 DPA/year gamma-induced displacement damage is found in the reflector of Evolutionary Pressurized Reactor (EPR). [ABSTRACT FROM AUTHOR]

Context. The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to 55° in latitude above and below the Galactic center (GC). Although the FBs were discovered eight years ago, their origin and the nature of the gamma-ray emission are still unresolved. Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin. Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC. Aims. We analyze nine years of Fermi Large Area Telescope data in order to study in more detail than the previous analyses the gamma-ray emission at the base of the FBs, especially at energies above 10 GeV. Methods. We used a template analysis method to model the observed gamma-ray data and calculate the residual emission after subtraction of the expected foreground and background emission components. Since there are large uncertainties in the determination of the Galactic gamma-ray emission toward the GC, we used several methods to derive Galactic gamma-ray diffuse emission and the contribution from point sources to estimate the uncertainties in the emission at the base of the FBs. Results. We confirm that the gamma-ray emission at the base of the FBs is well described by a simple power law up to 1 TeV energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV. It has larger intensity than the FBs emission at high latitudes and is shifted to the west (negative longitudes) from the GC. If the emission at the base of the FBs is indeed connected to the high-latitude FBs, then the shift of the emission to negative longitudes disfavors models in which the FBs are created by the supermassive black hole at the GC. We find that the gamma-ray spectrum can be explained either by gamma rays produced in hadronic interactions or by leptonic inverse Compton scattering. In the hadronic scenario, the emission at the base of the FBs can be explained either by several hundred supernova remnants (SNRs) near the GC or by about ten SNRs at a distance of ~1 kpc. In the leptonic scenario, the necessary number of SNRs that can produce the required density of CR electrons is a factor of a few larger than in the hadronic scenario. [ABSTRACT FROM AUTHOR]

Abstract Compton γ -ray sources have been in operation for over 30 years with new facilities being under construction or proposed. The gamma beam system under implementation at the Extreme Light Infrastructure - Nuclear Physics facility in Romania will deliver brilliant γ -ray beams with energies up to 19.5 MeV. Several instruments for measuring the parameters of the γ -ray beam are under development at ELI-NP. One of these instruments based on a High Purity Germanium detector is routinely used for beam energy measurements at other facilities. Here we investigate the use of a High Purity Germanium detector to continuously monitor the intensity of the ELI-NP gamma beam by measuring the inelastic scattering of photons. This method relies on both experimental and simulated data and it has been successfully tested during a recent experiment at the High Intensity γ -ray Source facility. [ABSTRACT FROM AUTHOR]

Computed Tomography (CT) using X-ray attenuation by atomic effects is now widely used for medical diagnosis and industrial non-destructive inspection. In this study, we performed a tomographic imaging of isotope (208Pb) distribution by the Nuclear Resonance Fluorescence (NRF), i.e. isotope specific resonant absorption and scattering of gamma rays, using Laser Compton Scattering (LCS) gamma rays. The NRF-CT image which includes both effects of atomic attenuation and nuclear resonant attenuation was obtained. By accounting for the atomic attenuation measured by a conventional method at the same time, a clear 208Pb isotope CT image was obtained. The contrast degradation due to notch refilling caused by small-angle Compton scattering is discussed. This study clearly demonstrates the capability of the isotope-specific CT imaging based on nuclear resonant attenuation which will be a realistic technique when the next generation of extremely intense LCS gamma-ray sources will be available. The expected image acquisition time using these intense LCS gamma rays was discussed. [ABSTRACT FROM AUTHOR]

Highlights • VHE gamma-ray observations of Mrk 421 with TACTIC during 2014-15. • Near simultaneous multi-wavelength data used to complement the TACTIC observations. • Variability analysis of multi-wavelength data from TeV to optical has been carried out. • Observed broad band spectral energy distribution has been reproduced using one zone leptonic SSC model. Abstract We observed the TeV blazar Mrk421 in the very high energy (VHE) region with TACTIC from 21 December, 2014 to 21 February, 2015. The VHE γ -ray signal is detected from the source at a statistical significance of ∼ 9 σ with 648 ± 74 γ -ray like events using a total observation time of 65.6 h of clean data. To denote the active period of the source, the entire observation has been divided into two spells: Spell I (21–30 December, 2014; MJD: 57012–57021) and Spell II (15 January-21 February, 2015; MJD: 57037–57074). The Spell I corresponds to relatively higher activity state wherein 337 ± 47 γ -rays are detected at a statistical significance of 7.39 σ in 21.7 h. During Spell II, 311 ± 57 γ -ray events have been detected in ∼ 44c at a statistical significance of 5.6 σ. The analysis of high energy (HE) γ -ray data from Fermi -LAT has been carried out for the period of TACTIC observations. In addition, near simultaneous multi-wavelength data from Swift -BAT and MAXI in the X-ray region, SPOL in optical V-band and OVRO at 15 GHz radio band have also been considered. The HE γ -ray and optical observations indicate variability during both the spells whereas hard X-ray observations are consistent with the average emission through out the TACTIC observations. The broad-band spectral energy distributions of the source are reproduced by single zone homogeneous synchrotron self Compton process for the two spells. The model parameters estimated for the two spells are similar except for the particle energy density which is obtained to be slightly higher during Spell I. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this study is to investigate the hidden corrosion at selected sites in corrosion simulated Mild Steel using information from the Compton scattered gamma rays. The proposed non-contact method employs a 137Cs source and an HPGe detector as part of the practical framework and it is integrated with the MCA system. The scattered gamma rays reflecting the corrosion is mapped in real time during the scanning of the specimen. Point by point scanning is carried out to acquire the pulse height spectrum and datas are used to determine the thickness of a known test object and hence thickness calibration is attained. With the calibration as a basis, hidden corrosion at the sub surfaces is detected and analysed. A reconstruction algorithm is explicated for this proposed work with a good precision of corrosion quantification in the subsequent layers. The precision is comparable with the radiography and transmission results. Experimental measurements and their results strongly confirm hidden corrosion to a depth of 4 mm (with a range of corrosion from 1.76 mm to 2.29 mm) in Mild Steel could be detected. Highlights • Compton photon scattering is explored as complementary technique for hidden corrosion inspection in Mild Steel. • A complete automated assembly of source, manipulator and detector are used. • Comprehensive evaluation of hidden corrosion in Mild Steel is provided. • The proposed method is validated by Radiography and Transmission technique. • Potential method for sub-surface and multilayered defect detection in complicated and inaccessible locations. [ABSTRACT FROM AUTHOR]

We present a design for a pixelated scintillator based gamma-ray spectrometer for non-linear inverse Compton scattering experiments. By colliding a laser wakefield accelerated electron beam with a tightly focused, intense laser pulse, gamma-ray photons up to 100 MeV energies and with few femtosecond duration may be produced. To measure the energy spectrum and angular distribution, a 33 × 47 array of cesium-iodide crystals was oriented such that the 47 crystal length axis was parallel to the gamma-ray beam and the 33 crystal length axis was oriented in the vertical direction. Using an iterative deconvolution method similar to the YOGI code, modeling of the scintillator response using GEANT4 and fitting to a quantum Monte Carlo calculated photon spectrum, we are able to extract the gamma ray spectra generated by the inverse Compton interaction. [ABSTRACT FROM AUTHOR]

We discuss gamma-ray signatures associated with an asymmetric explosion and transport of positrons in SN Ia ejecta. In particular, Compton scattering of gamma-ray line photons can induce polarization in the continuum, which would be a direct probe of the asymmetries in the distribution of radioactive isotopes and/or of the scattering medium. Even more interesting would be a comparison of the shapes of γ-ray lines and that of the electron–positron annihilation line at 511keV. The shapes of γ-ray lines associated with the decay of 56Co (e.g. lines at 847 and 1238keV) directly reflect the velocity distribution of 56Co. On the other hand, the 511 keV line arises from the annihilation of positions, which are also produced by the 56Co decay but can propagate through the ejecta before they slow down and annihilate. Therefore, the shape of the annihilation line might differ from other gamma-ray lines, providing constraints on the efficiency of positrons propagation through the ejecta and, as consequence, on the topology of magnetic fields in the ejecta and on the fraction of positrons that escape to the interstellar medium. We illustrate the above effects with two models aimed at capturing the main predicted signatures. [ABSTRACT FROM AUTHOR]

Even though high-quality X- and gamma rays with photon energy below mega-electron volt (MeV) are available from large-scale X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate bright gamma rays over 10 MeV. Recently, gamma rays with energies up to the MeV level were observed in Compton scattering experiments based on laser wakefield accelerators, but the yield efficiency was as low as 10-6, owing to low charge of the electron beam. Here, we propose a scheme to efficiently generate gamma rays of hundreds of MeV from submicrometer wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. The wiggling is caused by the quasistatic electric and magnetic fields induced around the wire surface, and these are so high that even quantum electrodynamics (QED) effects become significant for gamma-ray generation, although the driving lasers are only at the petawatt level. Our full 3D simulations show that directional, ultrabright gamma rays are generated, containing 1012 photons between 5 and 500 MeV within a 10-fs duration. The brilliance, up to 1027 photons s-1 mrad-2 mm-2 per 0.1% bandwidth at an average photon energy of 20 MeV, is second only to X-ray free electron lasers, while the photon energy is 3 orders of magnitude higher than the latter. In addition, the gamma ray yield efficiency approaches 10%-that is, 5 orders of magnitude higher than the Compton scattering based on laser wakefield accelerators. Such high-energy, ultrabright, femtosecond-duration gamma rays may find applications in nuclear photonics, radiotherapy, and laboratory astrophysics. [ABSTRACT FROM AUTHOR]

We study high-energy γ-rays observed from Cyg X-3 by the Fermi Large Area Telescope and the 15-GHz emission observed by the Ryle Telescope and the Arcminute Microkelvin Imager. We measure the γ-ray spectrum averaged over strong flares much more accurately than before and find it well modelled by Compton scattering of stellar radiation by relativistic electrons with the power-law index of ≃3.5 and a low-energy cutoff at the Lorentz factor of ∼103. We find a weaker spectrum in the soft spectral state but only upper limits in the hard and intermediate states. We measure strong orbital modulation during the flaring state, well modelled by anisotropic Compton scattering of blackbody photons from the donor by jet relativistic electrons. We discover a weaker orbital modulation of the 15-GHz radio emission, which is well modelled by free–free absorption by the stellar wind. We then study cross-correlations between radio, γ-ray, and X-ray emissions. We find the cross-correlation between the radio and γ-ray emission peaks at a lag less than 1 d, while we detect a distinct radio lag of ∼50 d with respect to the soft X-rays in the soft spectral state. [ABSTRACT FROM AUTHOR]

POLAR is a compact space-borne detector designed to perform reliable measurements of the polarization for transient sources like Gamma-Ray Bursts in the energy range 50–500 keV. The instrument works based on the Compton Scattering principle with the plastic scintillators as the main detection material along with the multi-anode photomultiplier tube. POLAR has been launched successfully onboard the Chinese space laboratory TG-2 on 15th September, 2016. In order to reliably reconstruct the polarization information a highly detailed understanding of the instrument is required for both data analysis and Monte Carlo studies. For this purpose a full study of the in-orbit performance was performed in order to obtain the instrument calibration parameters such as noise, pedestal, gain nonlinearity of the electronics, threshold, crosstalk and gain, as well as the effect of temperature on the above parameters. Furthermore the relationship between gain and high voltage of the multi-anode photomultiplier tube has been studied and the errors on all measurement values are presented. Finally the typical systematic error on polarization measurements of Gamma-Ray Bursts due to the measurement error of the calibration parameters are estimated using Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

To measure the temporal width and the intensity evolution versus time of a MeV gamma pulse generated by a Compton Scatter Source, a time–space conversion method is proposed. This design is based on the consideration that the temporal length of the MeV pulse is proportional to the spatial length of the pulse in a certain semiconductor. The spatial length and the intensity evolution versus time of the MeV pulse can be obtained by recording the region of the refractive index change that is induced by the MeV pulse. The simulation suggests that the equivalent temporal spread of a mono-energy MeV δ pulse in a bulk semiconductor is on the order of picoseconds and does not vary significantly with photon energy and material type. According to our analysis, the excess carrier generation time, excess carrier diffusion and recombination do not significantly influence the temporal resolution of this method. The temporal response of the refractive index change to a MeV pulse is also fast enough to meet the measurement requirements. The signal generation process for measuring a 10-ps MeV pulse with a 200-fs probe beam is analyzed, revealing that the transverse size of the MeV pulse does not influence the temporal resolution of this method. [ABSTRACT FROM AUTHOR]

Gamma rays interact with a material through photoelectric absorption, Compton scattering, Rayleigh scattering and Pair production in the intermediate energy range. The probability of occurrence of a particular type of process depends on the energy of incident gamma rays, atomic number of the material, scattering angle and geometrical conditions. Various radiological parameters for organic compounds, namely ethylene glycol (C 2 H 6 O 2 ), propylene glycol (C 3 H 8 O 2 ), glycerin (C 3 H 8 O 3 ), isoamyl alcohol (C 5 H 12 O), butanone (C 4 H 8 O), acetophenone (C 8 H 8 O 2 ), cyclohexanone (C 6 H 10 O), furfural (C 5 H 4 O 2 ), benzaldehyde (C 7 H 6 O), cinnamaldehyde (C 9 H 8 O), glutaraldehyde (C 5 H 8 O 2 ), aniline (C 6 H 7 N), benzyl amine (C 6 H 7 N), nitrobenzene (C 6 H 5 NO 2 ), ethyl benzene (C 8 H 10 ), ethyl formate (C 3 H 6 O 2 ) and water (H 2 O) are presented at 81, 122, 356 and 511 keV energies employing NaI(Tl) scintillation detector in narrow-beam transmission geometry. The radiation interaction parameters such as mass attenuation, molar extinction and mass energy absorption coefficients, half value layer, total atomic and effective electronic cross-sections and CT number have been evaluated for these organic compounds. The general trend of values of mass attenuation coefficients, half value layer, molar extinction coefficients, total atomic and effective electronic cross-sections and mass energy absorption coefficients shows a decrease with increase in incident gamma photon energy. The values of CT number are found to increases linearly with increase of effective atomic number (Z eff ). The variation in CT number around Z eff ≈ 3.3 shows the peak like structure with respect to water and the correlation between CT number and linear attenuation coefficient is about 0.99. Appropriate equations are fitted to these experimentally determined parameters for the organic compounds at incident photon energy ranging from 81 keV to 511 keV used in the present study. Experimental values are compared with the theoretical data obtained using WinXcom software package, and are found in good agreement. [ABSTRACT FROM AUTHOR]

A major breakthrough in our understanding of gamma-ray bursts (GRB) prompt emission physics occurred in the last few years, with the realization that a thermal component accompanies the over-all nonthermal prompt spectra. This thermal part is important by itself, as it provides direct probe of the physics in the innermost outflow regions. It further has an indirect importance, as a source of seed photons for inverse-Compton scattering, thereby it contributes to the nonthermal part as well. In this short review, we highlight some key recent developments. Observationally, although so far it was clearly identified only in a minority of bursts, there is indirect evidence that a thermal component exists in a very large fraction of GRBs, possibly close to 100%. Theoretically, the existence of a thermal component has a large number of implications as a probe of underlying GRB physics. Some surprising implications include its use as a probe of the jet dynamics, geometry and magnetization. [ABSTRACT FROM AUTHOR]

The effective atomic numbers of some transition and rare earth compounds have been determined by measuring the ratio of Rayleigh to Compton scattering signal using 59.5 keV gamma radiation from americium-241 radioactive source. The scattered gamma photons from the elements and compounds at an angle of 90° were detected using an ORTEC high-purity germanium detector coupled with 16K multi-channel analyzer. By measuring the ratio of Rayleigh to Compton scattered signal (momentum transfer 3.38 Å−1), the effective atomic numbers of the transition and rare earth compounds have been determined and compared with theoretical values predicted by AutoZeff, power law, and direct method. [ABSTRACT FROM PUBLISHER]

The CLAS and Hall A Collaborations at Jefferson Laboratory have recently released new results for the $ e p\rightarrow e p \gamma$ reaction. We analyze these new data within the Generalized Parton Distribution formalism. Employing a fitter algorithm introduced and used in earlier works, we are able to extract from these data new constraints on the kinematical dependence of three Compton Form Factors. Based on experimental data, we subsequently extract the dependence of the proton charge radius on the quarks' longitudinal momentum fraction. [ABSTRACT FROM AUTHOR]

A high-brilliance ( ∼ 10 22 photon s −1 mm −2 mrad −2 /0.1%) gamma-ray source experiment is currently being planned at Fermilab ( E γ ≃ 1.1 MeV). The source implements a high-repetition-rate inverse Compton scattering by colliding electron bunches formed in a ∼300-MeV superconducting linac with a high-intensity laser pulse. This paper describes the design rationale along with some of technical challenges associated to producing high-repetition-rate collision. The expected performances of the gamma-ray source are also presented. [ABSTRACT FROM AUTHOR]

The laser-Compton scattering (LCS) phenomenon is one known method for producing energetic and high-intensity gamma rays with variable photon spectrums. Availability of high-intensity gamma rays has made probing the (γ,n)-based photonuclear transmutation possible and worth consideration. Parametric studies of LCS have shown that the gamma ray’s spectrum is tunable and dependent upon various facility-related parameters. In this paper, a systematic optimization study of the LCS spectrum has been performed in view of the incident laser energy, electron beam energy and collimation angle. This optimization has been done with the aim to maximize the transmutation reaction rates of long-living fission products (LLFPs) such as 129 I, 135 Cs, and 137 Cs that have an isotopic composition of typical LWR spent fuel. In addition, the (γ,n) and (γ,2n)-reaction rates have been simultaneously calculated in order to evaluate the feasibility of photonuclear transmutation using the (γ,n)-reaction. It has been shown that careful optimization of the LCS spectrum noticeably enhances the (γ,n)-reaction rate without requiring any isotopic separation of the iodine and cesium targets. Furthermore, in order to enhance the energy efficiency of the LCS-based photo-transmutation system, a novel multiple laser-Compton scattering extraction (MULEX) concept has been introduced in this work, and it has been shown that the total production of the LCS photons can easily be increased by a factor of 10 or 20 in a single accelerator system. [ABSTRACT FROM AUTHOR]

The Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard cosmic ray electron population within the volume of the Bubbles, via inverse Compton scattering and synchrotron radiation, respectively. The relative rates of these processes are set by the relative energy density of the interstellar radiation field and the magnetic field within the Bubbles; consequently, under the hypothesis of a common origin, the combination of the gamma-ray and microwave measurements can be used to estimate the magnetic field within the Bubbles. We revisit the consistency of this hypothesis on a latitude-by-latitude basis, using data from Fermi, WMAP and Planck; estimate the variation of the electron spectrum within the Bubbles; and infer bounds on the magnetic field within the Bubbles as a function of distance from the Galactic plane. We find that while the microwave and gamma-ray spectra are generally consistent with the leptonic hypothesis for few-microGauss magnetic fields, there appears to be a preference for spectral hardening in the microwaves at mid-latitudes (especially in the ∣b∣ ~ 25°-35° range) that is not mirrored in the gamma-rays. This result may hint at a non-leptonic contribution to the gamma-ray spectra; however, the discrepancy can be reconciled in purely leptonic models if the cut-off energy for the electrons is lower in this latitude range and the spectrum below the cut-off is harder. [ABSTRACT FROM AUTHOR]

The general sourceless efficiency calibration has two major methods, Monte Carlo simulation and numerical calculation. Monte Carlo simulation as an important method to address the efficiency calibration in complex measurement systems, despite it being highly accurate, but inefficient and time-consuming. And although the numerical calculation is computationally efficient, its accuracy is highly influenced by the multiple Compton scattering of rays in sensitive body, and it is difficult to deal with complex measurement systems. To solve the above problems, this paper proposes a discrete numerical calculation combined with the graphical Boolean operations method for sourceless efficiency calibration. The method starts with a Monte Carlo simulation to obtain the rays deposition process in an infinite sensitive body and record deposition locations as a matrix; then, for different measurement systems, discrete numerical calculations are used to rapidly obtain the transmission process of rays to the sensitive body of the detector; finally, the two are combined to obtain the detection efficiency of the rays by using graphical Boolean operations. For the given two test models, the error between the measured and calculated results of 241Am, 137Cs, 60Co at 60 positions is within -3.61∼9.71%, and the error between the measured and calculated results of the soil source is within -1.27 to 4.26%, indicating that the method has high reliability in sourceless efficiency calibration. And in comparison with Monte Carlo simulations, it is found that the method has a good agreement with Monte Carlo simulation in efficiency calibration and the computational speed has been greatly improved. • A novel gamma-ray sourceless efficiency calibration method. • Solved the problem of multiple Compton scattering in the sensitive body of the detector in the numerical method. • Computational speed was greatly improved compared to Monte Carlo simulation. [ABSTRACT FROM AUTHOR]