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To explore the potential of utilizing Compton scattered x-ray photons for imaging applications, it is critical to accurately evaluate scattered x-ray transmission properties of targeted tissue materials. In this study, scattered x-ray transmission of breast tissue equivalent phantoms was evaluated. Firstly, two validations were carried out using a primary x-ray beam at 80 kVp with both experimental measurement (ion chamber with narrow-beam setup) and analytical calculation (Spektr toolkit). The tungsten-anode x-ray spectrum model was thus validated by measuring and calculating the transmission through increasing thickness of 1100 Aluminum filters. Similarly, the composition models of breast tissue equivalent phantoms (CIRS, 012A) were validated by measuring and calculating x-ray transmission for three different breast compositions (BR30/70, BR50/50, and BR70/30). Following validation, transmission properties of Compton scattered x-ray photons were measured with a GOS based linear array detector at the 90° angle from the primary beam. The same study was performed through three independent approaches: experimental measurement, analytical calculation, and Monte Carlo simulation (GEANT4). For all three methods, the scattered x-ray photon transmission as functions of phantom thickness were determined and fit into exponential functions. The transmission curves from all three methods matched reasonably well, with a maximum difference of 6.3% for the estimated effective attenuation coefficients of the BR50/50 phantom. The relative difference among the three methods of estimated attenuation is under 3.5%. As an initial step to develop a novel Compton scatter-based breast imaging system, the quantitative results from this study paved a fundamental base for future work., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Fully polarized Compton scattering from a beam of spin-polarized electrons is investigated in plane-wave backgrounds in a broad intensity region from the perturbative to the nonperturbative regimes. In the perturbative regime, polarized linear Compton scattering is considered for investigating polarization transfer from a single laser photon to a scattered photon, and in the high-intensity region, the polarized locally monochromatic approximation and locally constant field approximation are established and are employed to study polarization transfer from an incoming electron to a scattered photon. The numerical results suggest an appreciable improvement of about 10% in the scattering probability in the intermediate-intensity region if the electron's longitudinal spin is parallel to the laser rotation. The longitudinal spin of the incoming electron can be transferred to the scattered photon with an efficiency that increases with laser intensity and collisional energy. For collision between an optical laser with frequency ∼1 eV and a 10 GeV electron, this polarization transfer efficiency can increase from about 20% in the perturbative regime to about 50% in the nonperturbative regime for scattered photons with relatively high energy. [ABSTRACT FROM AUTHOR]

The design and parameters of scintillation detectors of Compton polarimeters for measuring photons formed during the annihilation of electron-positron pairs at rest are considered. The discussed setup makes it possible to measure and compare the polarization correlations of scattered annihilation photons in these two quantum states. The amplitude parameters of scatterers and scattered photon detectors obtained from preliminary tests of these detectors using radioactive gamma sources, as well as in the process of collecting experimental data, are given. The possibility of measuring and comparing the polarization correlations of scattered annihilation photons is shown. [ABSTRACT FROM AUTHOR]

Recently, a γ γ collider based on the existing 17.5 GeV linac of the European XFEL has been proposed. High-energy photons will be generated by Compton scattering of laser photons with a wavelength of 0.5–1 μ m on electrons. Such a photon collider covers the range of invariant masses W γ γ < 12 Ge V / c 2 . The physics program includes spectroscopy of C -even resonances (c-, b-quarkonia, 4-quark states, glueballs) in various J P states. Variable circular and linear polarizations will help in determining the quantum numbers. In this paper, we present a summary of measured and predicted two-photon widths of various resonances in the mass region 3–12 Ge V / c 2 and investigate the experimental possibility of observing these heavy two-photon resonances under the conditions of a large multi-hadron background. Registration of all final particles is assumed. The minimum values of Γ γ γ (W) are obtained at which resonances can be detected at a 5 σ confidence level in 1 year of operation. [ABSTRACT FROM AUTHOR]

Magnetar giant flares (MGFs) have been long proposed to contribute at least a subsample of the observed short gamma-ray bursts (GRBs). The recent discovery of the short GRB 200415A in the nearby galaxy NGC 253 established a textbook-version connection between these two phenomena. Unlike previous observations of the Galactic MGFs, the unsaturated instrument spectra of GRB 200415A provide for the first time an opportunity to test the theoretical models with the observed γ-ray photons. This paper proposed a new readily fit-able model for the MGFs, which invokes an expanding fireball Comptonized by the relativistic magnetar wind at photosphere radius. In this model, a large amount of energy is released from the magnetar crust due to the magnetic reconnection or the starquakes of the star surface and is injected into confined field lines, forming a trapped fireball bubble. After breaking through the shackles and expanding to the photospheric radius, the thermal photons of the fireball are eventually Comptonized by the relativistic e ± pairs in the magnetar wind region, which produces additional higher-energy gamma-ray emission. The model predicts a modified thermal-like spectrum characterized by a low-energy component in the Rayleigh-Jeans regime, a smooth component affected by coherent Compton scattering in the intermediate energy range, and a high-energy tail due to the inverse Compton process. By performing a Monte-Carlo fit to the observational spectra of GRB 200415A, we found that the observation of the burst is entirely consistent with our model predictions. [ABSTRACT FROM AUTHOR]

A numerical model was developed and a system of the nonlinear equations of deuteriumtritium burn-up in inertial confinement fusion have been solved to find the minimum conditions which are required for the formation of hot spot and starting the thermonuclear reactions in a self-sustaining mode. The effect of all the dominant phenomena in the nonequilibrium plasma, including the alpha particle energy deposition in the hot spot and transferring to ions and electrons, ions-electron coupling energy, and the main photons-matter interactions, which includes the bremsstrahlung radiation and the Compton scattering, were investigated. By using the Klein-Nishina equation for scattering cross-section of high energy photons, the effects of the photon-matter interactions from a relativistic point of view have also been studied. It was shown that the change of photon distribution shape can have a significant effect on the photon temperature, the photon-electron coupling energy and as a result on the electrons and the ions temperature in a diluted plasma. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of University of Anbar for Pure Science is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Compton scattering of polarized radiation by a nondegenerate and unpolarized electron gas is examined. Two polarization bases are introduced for pulses of photons: external, connected with the geometry of the medium and internal, connected with a scattering event. Starting with a general relativistic kinetic equation describing the multiple effect of the mechanism taking induced processes into account, it is shown that for describing a stationary, azimuthally independent radiation field in a plane layer, two Stokes parameters for linear polarization are sufficient. The features of the redistribution functions (RF) in frequency and direction are clarified, as well as the rotation angles from internal bases to external ones, and back which arise with forward and backward scattering. An algorithm is proposed for eliminating singularities during azimuthal averaging. The azimuthal averages from the most singular term of the RF are expressed in terms of elliptical integrals of the first kind. [ABSTRACT FROM AUTHOR]

In the present paper, the process of inverse double-Compton (IDC) scattering is considered in the context of astrophysical applications. It is assumed that the two hard X-ray photons emitted from an astrophysical source are scattered on a free electron and converted into a single soft photon of optical range. Using the QED S-matrix formalism for the derivation of a cross-section of direct double-Compton (DDC) scattering and assuming detailed balance conditions, an analytical expression for the cross-section of the IDC process is presented. It is shown that at fixed energies of incident photons, the inverse cross-section has no infrared divergences, and its behavior is completely defined by the spectral characteristics of the photon source itself, in particular by the finite interaction time of radiation with an electron. Thus, even for the direct process, the problem of resolving infrared divergence actually refers to a real physical source of radiation in which photons are never actually plane waves. As a result, the physical frequency profile of the scattered radiation for DDC as well as for IDC processes is a function of both the intensity and line shape of the incident photon field. [ABSTRACT FROM AUTHOR]

We investigate the radiation fields around super-Eddington accretion flow, in which multiple inverse-Compton scattering plays a principal role, by using newly developed code describing Boltzmann radiation transfer in the Schwarzschild space-time. We apply this code to post-processing spectral calculations based on general relativistic, radiation magnetohydrodynamic simulation data to obtain X-ray spectra seen from various viewing angles. The radiation fields are distinctively separated into a funnel region with an opening angle of ∼30°, which is full with hot (gas temperature of T > 108 K), tenuous, and high-velocity plasmas, and surrounding cooler (T ∼ 107 K) and optically thick outflow regions. Accordingly, there is a clear tendency that the smaller the viewing angle, the harder the spectra. In particular, hard photons with several tens of keV are observable only by observers at viewing angles less than ∼30°, consistent with past spectral studies based on simulations. Further, we investigate how the spectra are varied by a flare occurring in the innermost region, finding that the variation amplitude grows as the photon energy increases and that the harder photons emerge more quickly than softer photons. The observational implications on long-term spectral variability of ultra-luminous X-ray sources are briefly discussed. [ABSTRACT FROM AUTHOR]

The present work theoretically investigates the probability of generation of entangled electron–photon pair in high-energy Compton scattering of unpolarized electrons and photons due to scattering-channel-exchange mechanism. The study suggests that the scattering of unpolarized electrons and photons with nearly equal energy of the order of MeV at cross-channel can create entangled pair of up-spin electron and RCP photon or down-spin electron and LCP photon. The entanglement is quite strong exhibiting jump-concurrence for particular directions of scattering, however not limited by the Kapitza–Dirac restriction. Such strong electron–photon entanglement is observed to be highly selective along the directions of scattering on the surface of two opposite cones at 45° around the electron-detector axis and on the plane perpendicular to it, the latter one exhibiting maximal entanglement. The work predicts that spin-polarization entangled electron–photon pairs are highly possible to be found in practical experiments of high-energy Compton scattering with specific directional selectivity. [ABSTRACT FROM AUTHOR]

For magnetic fields larger than the characteristic scale linked to axion-electrodynamics, quantum vacuum fluctuations due to axion-like fields can dominate over those associated with the electron-positron fields. This conjecture is explored by investigating both the axion-modified photon capture by a strong magnetic field and the Coulomb potential of a static pointlike charge. We show that in magnetic fields characteristic of neutron stars ∼ 10 13 – 10 15 G , the capture of gamma photons prior to the production of a pair can prevent the existence of an electron-positron plasma, essential for explaining the pulsar radiation mechanism. This incompatibility is used to limit the axion parameter space. Our bounds improve existing outcomes in the region of mass m ∼ 10 - 10 – 10 - 5 eV . The effect of capture, known in QED as relating to gamma-quanta, is extended in axion electrodynamics to include X-ray photons with the result that a specially polarized part of the heat radiation from the surface is canalized along the magnetic field. Besides, we find that in the regime in which the dominance takes place, the running QED coupling depends on the field strength and the modified Coulomb potential is of Yukawa-type in the direction perpendicular to the magnetic field at distances much smaller than the axion Compton wavelength, while along the field it follows approximately the Coulomb law at any length scale. Despite the Coulomb singularity manifested in the latter case, we argue that the ground-state energy of a non-relativistic hydrogen atom placed in a strong magnetic field turns out to be bounded due to the nonrenormalizable feature of axion-electrodynamics. [ABSTRACT FROM AUTHOR]

The Fermi-LAT collaboration presented the second gamma-ray burst (GRB) catalog covering its first 10 years of operations. A significant fraction of afterglow-phase light curves in this catalog cannot be explained by the closure relations of the standard synchrotron forward-shock model, suggesting that there could be an important contribution from another process. In view of the above, we derive the synchrotron self-Compton (SSC) light curves from the reverse shock in the thick- and thin-shell regime for a uniform-density medium. We show that this emission could explain the GeV flares exhibited in some LAT light curves. Additionally, we demonstrate that the passage of the forward shock synchrotron cooling break through the LAT band from jets expanding in a uniform-density environment may be responsible for the late time (≈102 s) steepening of LAT GRB afterglow light curves. As a particular case, we model the LAT light curve of GRB 160509A that exhibited a GeV flare together with a break in the long-lasting emission, and also two very high energy photons with energies of 51.9 and 41.5 GeV observed 76.5 and 242 s after the onset of the burst, respectively. Constraining the microphysical parameters and the circumburst density from the afterglow observations, we show that the GeV flare is consistent with an SSC reverse-shock model, the break in the long-lasting emission with the passage of the synchrotron cooling break through the Fermi-LAT band, and the very energetic photons with SSC emission from the forward shock, when the outflow carries a significant magnetic field (RB ≃ 30) and it decelerates in a uniform-density medium with a very low density (). [ABSTRACT FROM AUTHOR]

We predict theoretically the leading role and angular anisotropy of bremsstrahlung in resonant Compton scattering of a hard X-ray photon by an atom. [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]

Introduction: Cadmium zinc telluride has recently been used as a compound semiconductor detector in a wide range of fields. The current study is a comprehensive investigation of the performance of this detector against the photon beam. Moreover, a comparative study was carried out with other common detectors using the Mote Carlo code by the implementation of the same strategy. Material and Methods: During the simulation by FLUKA code, a number of photons were regarded as primary particles. It is attractive to trace each incident photon uniquely considering all possible collisions and produced secondary particles at the microdosimetry scale. In the current study, the coordinate of threedimensional collisions location was realized at detector sensitive volume. Moreover, energy deposition was considered at each unique collision and through all interactions, totally. In addition, the physical concepts of photon interaction with detector volume were assessed, numerically. Furthermore, the effect of gold foils implemented as electrode at both sides of the detector was taken into account. Results: The obtained results indicated the context of photoelectric and Compton scattering in photon interactions with CZT, including the number of interactions, the deposited energy, and three-dimensional collision coordinate, while the latter case is proposed as a new achievement. Conclusion: As evidenced by the obtained results, the performance of this detector can be improved by changing material fraction and detector dimension to achieve optimum efficiency. In addition, the comparative results demonstrated that the efficiency of CZT covered by gold electrodes is superior to other common available semi-conductor detectors. [ABSTRACT FROM AUTHOR]

New experimental data on the multifragmentation of carbon nuclei that is initiated by the photoproduction of neutral pions and eta mesons are discussed. The novelty is associated with the exclusive character of the processes being studied, in which case a determination of partial meson-photoproduction reactions is followed by an analysis of complementary particles for coincidence. The experiment being discussed was performed by the GRAAL (GRenoble Accelerateur Anneau Laser) Collaboration in a beam of 500- to 1500-MeV Compton photons. The possibility of performing new experiments within the BGO-OD Collaboration (Bonn, Germany) is considered. A new method for studying the interaction of short-lived mesons with nuclei on the basis of detecting cascade recoil nucleons is proposed. [ABSTRACT FROM AUTHOR]

We report on orbital modulation of the 100–600 MeV gamma-ray emission of the PB = 4.6 hr millisecond pulsar binary PSR J2339−0533 using 11 yr of Fermi Large Area Telescope data. The modulation has high significance (chance probability p ≈ 10−7), is approximately sinusoidal, peaks near pulsar superior conjunction, and is detected only in the low-energy 100–600 MeV band. The modulation is confined to the on-pulse interval, suggesting that the variation is in the 2.9 ms pulsed signal itself. This contrasts with the few other known systems exhibiting GeV orbital modulations, as these are unpulsed and generally associated with beamed emission from an intrabinary shock. The origin of the modulated pulsed signal is not yet clear, although we describe several scenarios, including Compton upscattering of photons from the heated companion. This would require high coherence in the striped pulsar wind. [ABSTRACT FROM AUTHOR]

We calculate differential and integrated cross sections for the Compton interaction as well as mass attenuation (), mass energy-transfer (), and mass energy-absorption () coefficients, within the relativistic impulse approximation (RIA) using Compton profiles (CPs) obtained from unrestricted Hartree–Fock electron densities. We investigate the impact of using molecular as opposed to atomic CPs on dosimetric photon interaction coefficients for air, water and graphite, and compare our cross sections to the simpler Waller–Hartree (WH) and Klein–Nishina (KN) formalisms. We find that differences in and resulting from the choice of CPs within the RIA are small relative to the differences between the RIA, WH, and KN calculations. Surprisingly, although the WH binding corrections seem accurate when considering , there are significant discrepancies between the WH and RIA results when we look at. The WH theory can differ substantially from the predictions of KN and the RIA in the tens of keV range (e.g. 6%–10% at 20 keV), when Compton scattering becomes the dominant interaction mechanism. For lower energies, the disagreement further grows to about one order of magnitude at 1 keV. However, since the photoelectric effect transfers more energy than the Compton interaction in the tens of keV range and below, the differences in the total values resulting from the choice of Compton models (KN, WH, or RIA) are not larger than 0.4%, and the differences between WH and the other two theories are no longer prominent. [ABSTRACT FROM AUTHOR]

In this paper we study photon emission in the interaction of the laser beam with an under-dense target and the attached reflecting plasma mirror. Photons are emitted due to the inverse Compton scattering when accelerated electrons interact with a reflected part of the laser pulse. The enhancement of photon generation in this configuration lies in using the laser pulse with a steep rising edge. Such a laser pulse can be obtained by the preceding interaction of the incoming laser pulse with a thin solid-density foil. Using numerical simulations we study how such a laser pulse affects photon emission. As a result of employing a laser pulse with a steep rising edge, accelerated electrons can interact directly with the most intense part of the laser pulse that enhances photon emission. This approach increases the number of created photons and improves photon beam divergence. [ABSTRACT FROM AUTHOR]

Here, we consider axially symmetric, stationary, rotating and charged Kerr–Sen Dilaton-Axion black hole as particle accelerator. We find the effective potential and discuss the circular orbit of a particle. We investigate the center of mass energy of two colliding neutral particles with different rest masses falling from rest at infinity to near the non-extremal horizons (event horizon and Cauchy horizon) and extremal horizon of the Kerr–Sen Dilaton-Axion black hole. Analogous to the Compton process, we discuss the collision of a particle and a massless photon. Finally, we find the center of mass energy due to the collision of two photons in the background of Kerr–Sen Dilaton-Axion black hole. [ABSTRACT FROM AUTHOR]

We study amplitudes of the inclusive photon induced high-energy processes: elastic Compton scattering off hadrons and photoproduction. Although description of these amplitudes includes both non-perturbative and perturbative contributions, QCD factorization makes possible to study them separately. Throughout the present paper we focus on the perturbative amplitudes and study such amplitudes in all available in the literature forms of QCD factorization: Collinear, K T and Basic. As a result, we obtain expressions for the perturbative Compton amplitudes, which can be used at arbitrary x and Q 2 in any form of QCD factorization. Putting Q 2 = 0 in those expressions allows us to obtain expressions for the perturbative components of the photoproduction amplitudes. The small-x asymptotics of the Compton amplitudes in any form of QCD factorization are of the Regge type, with the Reggeon being a double-logarithmic (non-BFKL) contribution to Pomeron. [ABSTRACT FROM AUTHOR]

A set of natural units is determined from the "photon element" model of light, the outcome of an extended Compton analysis. In terms of these units, the speed of light and the electrical and Boltzmann constants are, respectively, on the order of unity, but the Planck constant is ~1027 or greater and gravitational constant ~10-59 or greater. This makes the photon element units less convenient than the Planck units. With the mass unit that is only ~10-43 of the Planck mass, however, the photon element units can correspond better to physical realities than the Planck units. For the spacetime, a photon element forms a set of unit base vectors, a natural basis that is Lorentz covariant. There an analysis shows that (1) of the above five universal constants all are Lorentz invariants except the gravitational constant, and (2) of the five natural units (time, length, mass, electrical charge, and temperature,) only the electrical charge is a Lorentz invariant. [ABSTRACT FROM AUTHOR]

Electric force is presently the only means in laboratory to accelerate charged particles to high energies, corresponding acceleration processes are classical and continuous. Here we report on how to accelerate electrons and positrons to high energies using ultra intense lasers (UIL) through two quantum processes, nonlinear Compton scattering and nonlinear Breit-Wheeler process. In the coherent photon dominated regime of these two processes, the former can effectively boost electrons/positrons and the latter can produce high energy electrons and positrons with low energy γ photons. The energy needed for such quantum acceleration (QA) is transferred from large numbers of coherent laser photons through the two quantum processes. QA also collimate the generated high energy electrons and positrons along the laser axis and the effective acceleration distance is of microscopic dimensions. Proof of principle QA experiment can be performed on 100 petawatt (PW) scale lasers which are in building or planning. [ABSTRACT FROM AUTHOR]

• A new photon and neutron hybrid transmutation method for Cs-135, Cs-137, and I-129. • A two-step approach in which (γ,n) transmutation is followed by (n,γ) transmutation. • (n,γ) transmutation is a result of (γ,n) transmutation, therefore, cost-effective. This work is concerned with transmutation of the highly toxic radioactive Cs-135 and Cs-137, which are extremely difficult to transmute in the conventional neutron fields, together with I-129. A novel strategy of photon and neutron hybrid transmutation has been proposed for a CsI target. An optimized laser-Compton scattering (LCS) source is used to generate energetic gamma-rays, which are then directed to central CsI target for photonuclear (γ,n) transmutation. Energetic neutrons resulting from the (γ,n) reactions are scattered through moderator into a surrounding CsI blanket targets where they undergo (n,γ) transmutation. In this study, design parameters such as LCS spectrum, target dimensions and configurations have been optimized to enhance the effectiveness of the hybrid transmutation method. In addition, the CsI target configuration has also been optimized to remove heat deposited in the central target. From the results, it has been concluded that the hybrid transmutation has promising applications for the radioactive waste management. [ABSTRACT FROM AUTHOR]

In this article, we discuss a scaling function for the cross section in deeply virtual compton scattering (DVCS) and exclusive vector meson production in both γ*p and γ*A processes. Our description relies on the geometric scaling phenomenon in which cross sections are a function of a single variable τ=Q2/Qs2, where Q2 is the photon virtuality and Qs2 represents the saturation scale that drives the energy dependence and nuclear effects. We make a prediction to be tested in future electron–ion colliders. [ABSTRACT FROM AUTHOR]

The scintillation properties of cesium-zirconium hexachloride (Cs 2 ZrCl 6) were investigated by γ-ray spectrometry and the Compton Coincidence Technique. The tested cylindrical sample had 20 mm diameter and 12 mm height. The crystal shows a high light output of 40 900 photons per MeV as measured by a spectroscopy type photomultiplier with 20 μs pulse integration time under γ-ray excitation at room temperature. A small deviation from linear response as a function of energy deposited in γ-ray absorption or Compton scattering processes, combined with a high light yield, results in good energy resolution equal to 4.3 % at 662 keV and 2.3 % at 2.6 MeV. Due to long lasting scintillation decay the sample properties were studied at different shaping time constants in an analogue spectroscopy chain or using different integration time gates when employing a digital analyzer. [ABSTRACT FROM AUTHOR]

Cargo containers constitute the most critical component of global trade: 108 million containers represent the movement of about 95% of the world’s manufactured goods. The steady increase in cargo container shipments has had a profound effect on world security: the threat associated with smuggling of shielded special nuclear material is elevated every year. Containers reaching the borders of the U.S. are currently not radiographically inspected due to time and dose considerations stemming from the use of bremsstrahlung beams for imaging. Bremsstrahlung spectra are low-energy peaked, resulting in low penetration values, especially through dense cargoes. The use of monoenergetic radiography beams could alleviate many of these problems due to higher energy and low background continuum. Using Monte Carlo simulations of a realistic imaging scenario with support from previous experimental measurements, we demonstrate how the use of monoenergetic photon beams in radiography can simultaneously reduce the radiation dose imparted to the cargo and any potential stowaways while increasing image quality. Dual-energy methods are leveraged to calculate material atomic number. Image quality is evaluated by measuring the noise standard deviation, contrast-to-noise ratio, and the pixel error as the dose is decreased. [ABSTRACT FROM AUTHOR]

The total mass attenuation coefficients (μ/ρ) of oxide dispersion strengthened (ODS) steels have been investigated by using Geant4 simulation toolkit at energies ranging from 0.01 MeV to 100 GeV. Moreover, Geant4 is applied to further study on the partial mass attenuation coefficient of three main interactions including photoelectric effect, compton scattering, gamma conversion between incident photon and ODS steels. Then molecular cross-section (σ m) and mean free path (λ) are obtained by the total mass attenuation coefficients. The results obtained by Geant4 are compared with those obtained by experiments and XCOM program and these results agree with each other very well. It is concluded that Geant4 Monte Carlo toolkit is a powerful tool in studying interaction of photons in material and energies. The shielding parameters of ODS steels presented in this paper can be very useful for the potential nuclear application and other industries in future. • The μ/ρ of ODS steels have been studied by Geant4 at energies from 0.01 MeV to 100 GeV. • The results gained by Geant4 agree with those gained by experiments and XCOM well. • The partial μ/ρ of three main interactions between photon and ODS steels are studied. [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]

We present a high-resolution X-ray spectrum of the accreting X-ray pulsar OAO 1657 – 415 obtained with HETG + ACIS-S onboard Chandra, revealing the presence of a broad line component around ∼6.3 keV associated with the neutral iron Kα line at 6.4 keV. This is interpreted as a Compton shoulder arising from the Compton-scattering of the 6.4-keV fluorescence photons, making OAO 1657–415 the second accreting neutron star in which such a feature has been detected. A Compton shoulder reveals the presence of dense matter surrounding the X-ray source. We did not detect any periodicity in the light-curve and we obtained an upper limit of ∼2 per cent for the pulse fraction during this observation. This could be a result of the smearing of the pulses when X-ray photons are scattered from a large region around the neutron star. In addition to the Fe Kα, Fe Kβ and Ni Kα lines already reported for this source, we report for the first time the presence of He-like and H-like iron emission lines at 6.7 and 6.97 keV in the first-order HETG spectrum. The detection of such ionized lines, indicative of a highly ionized surrounding medium, is rare in X-ray binaries. [ABSTRACT FROM AUTHOR]

Imaging was conducted using an electron tracking-Compton camera (ETCC), which measures γ-rays with energies in the range of 200–900 keV from 95mTc. 95mTc was produced by the 95Mo(p, n)95mTc reaction on a 95Mo-enriched target. A method for recycling 95Mo-enriched molybdenum trioxide was employed, and the recycled yield of 95Mo was 70%-90%. Images were obtained with the gate of three energies. The results showed that the spatial resolution increases with increasing γ-ray energy, and suggested that the ETCC with high-energy γ-ray emitters such as 95mTc is useful for the medical imaging of deep tissue and organs in the human body. [ABSTRACT FROM AUTHOR]

About one third of all deaths worldwide can be traced back to cardiovascular diseases. An interventional radiology procedure for their diagnosis is Digital Subtraction Angiography (DSA). An alternative to DSA is K-Edge subtraction (KES) imaging, which has been shown to be advantageous for moving organs and eliminating image artifacts caused by patient movement. As highly brilliant, monochromatic X-rays are required for this method, it has been limited to synchrotron facilities so far, restraining the feasibility in clinical routine. Compact synchrotron X-ray sources based on inverse Compton scattering, which have been evolving substantially over the past decade, provide X-rays with sufficient brilliance that meet spatial and financial requirements affordable in laboratory settings or for university hospitals. In this work, we demonstrate a first proof-of-principle K-edge subtraction imaging experiment using the Munich Compact Light Source (MuCLS), the first user-dedicated installation of a compact synchrotron X-ray source worldwide. It is shown experimentally that the technique of KES increases the visibility of small blood vessels overlaid by bone structures. [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]

The accuracy of activity determination for activated nuclide 56Mn is the key to the manganese bath method applying to the characterization of radionuclide neutron source. As an alternative to the 4π(Č)-γ method, TDCR-Čerenkov method could also be applied to the measurement of 56Mn in the manganese bath device, if the existing calculation model is extended. There are two difficulties when the existing TDCR-Čerenkov method is applied to the activity determination of 56Mn. One is that the efficiency computation of gamma transitions, and the other is the interference contributed by Čerenkov photons emitted in the photomultiplier windows induced by Compton scattering. In this study, the above two difficulties are solved by extending the calculation model. For efficiency computation, the decay scheme of 56Mn is taken into account in the calculation of efficiency. Among them, the efficiency of gamma transition is calculated from the simulated secondary electronic spectra. In addition, Čerenkov photons emitted in photomultiplier windows are corrected by additional light proof experiment and improved calculation model. The results derived from this extended method are in good agreement with other standardization technique. • 56Mn is measured by means of TDCR counter. • The TDCR-Čerenkov method is extended for complex decay schemes. • The interference contributed by Čerenkov photons emitted in the PMT induced by Compton scattering is corrected. [ABSTRACT FROM AUTHOR]

Single- and multi-photon spectra of pulsed γ -ray beams produced at 17, 34, and 40 MeV in the laser Compton scattering were measured with an 8” × 12” NaI(Tl) detector. By using the experimental single-photon spectra as the probability function of generating random numbers, response functions of the NaI(Tl) detector to j -fold photons ( j = 2, 3, 4 ...) were constructed. The least-square fits to the experimental multi-photon spectra by the Poisson distribution consisting of the response functions were made. The multi-photon spectra measured at 17 and 34 MeV follow the Poisson distribution. A quenching phenomenon of multi-photon spectra was observed for 40 MeV γ -rays as a result of the saturation at the photomultiplier tube of the NaI(Tl) detector. The original Poisson distributions were restored from the quenched spectra using a saturation curve in the form of y = a ⋅ x η with η =e − b x . We discuss the accuracy of photon-flux determination. [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]

We describe polarization of the Sunyaev--Zel'dovich (SZ) effect associated with electron pressure anisotropy likely present in the intracluster medium (ICM). The ICM is an astrophysical example of a weakly collisional plasma where the Larmor frequencies of charged particles greatly exceed their collision frequencies. This permits formation of pressure anisotropies, driven by evolving magnetic fields via adiabatic invariance, or by heat fluxes. SZ polarization arises in the process of Compton scattering of the cosmic microwave background (CMB) photons off the thermal ICM electrons due to the difference in the characteristic thermal velocities of the electrons along two mutually orthogonal directions in the sky plane. The signal scales linearly with the optical depth of the region containing large-scale correlated anisotropy, and with the degree of anisotropy itself. It has the same spectral dependence as the polarization induced by cluster motion with respect to the CMB frame (kinematic SZ effect polarization), but can be distinguished by its spatial pattern. For the illustrative case of a galaxy cluster with a cold front, where electron transport is mediated by Coulomb collisions, we estimate the CMB polarization degree at the level of 10-8 (~10 nK). An increase of the effective electron collisionality due to plasma instabilities will reduce the effect. Such polarization, therefore, may be an independent probe of the electron collisionality in the ICM, which is one of the key properties of a high-β weakly collisional plasma from the point of view of both astrophysics and plasma theory. [ABSTRACT FROM AUTHOR]

We explore the physics of relativistic radiation-mediated shocks (RRMSs) in the regime where photon advection dominates over photon generation. For this purpose, a novel iterative method for deriving a self-consistent steady-state structure of RRMS is developed, based on a Monte Carlo code that solves the transfer of photons subject to Compton scattering and pair production/annihilation. Systematic study is performed by imposing various upstream conditions which are characterized by the following three parameters: the photon-to-baryon inertia ratio ξ u*, the photon-to-baryon number ratio ñ, and the shock Lorentz factor γ u. We find that the properties of RRMSs vary considerably with these parameters. In particular, while a smooth decline in the velocity, accompanied by a gradual temperature increase is seen for ξ u* ≫1, an efficient bulk Comptonization, that leads to a heating precursor, is found for ξ u* ≲ 1. As a consequence, although particle acceleration is highly inefficient in these shocks, a broad non-thermal spectrum is produced in the latter case. The generation of high-energy photons through bulk Comptonization leads, in certain cases, to a copious production of pairs that provide the dominant opacity for Compton scattering. We also find that for certain upstream conditions a weak subshock appears within the flow. For a choice of parameters suitable to gamma-ray bursts, the radiation spectrum within the shock is found to be compatible with that of the prompt emission, suggesting that subphotospheric shocks may give rise to the observed non-thermal features despite the absence of accelerated particles. [ABSTRACT FROM AUTHOR]

The Real Compton Scattering in ultraperipheral pPb collisions at RHIC and LHC energies is investigated and predictions for the squared transverse momentum ( t ) and rapidity ( Y ) distributions are presented. The scattering amplitude is assumed to be given by the sum of the Reggeon and Pomeron contributions and the Pomeron one is described by the Color Dipole formalism taking into account the non-linear (saturation) effects in the QCD dynamics. We demonstrate that the behavior of the cross sections at large- t and/or Y is dominated by the Pomeron contribution and is strongly affected by the non-linear effects present in the QCD dynamics. These results indicate that a future experimental analysis of this process can be useful to probe the QCD dynamics at high energies. [ABSTRACT FROM AUTHOR]

The internal structure of nucleons (protons and neutrons) remains one of the greatest outstanding problems in modern nuclear physics. By scattering high-energy electrons off a proton we are able to resolve its fundamental constituents and probe their momenta and positions. Here we investigate the dynamics of quarks and gluons inside nucleons using deeply virtual Compton scattering (DVCS)--a highly virtual photon scatters off the proton, which subsequently radiates a photon. DVCS interferes with the Bethe-Heitler (BH) process, where the photon is emitted by the electron rather than the proton. We report herein the full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the regime where the scattering is expected to occur off a single quark, measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction. [ABSTRACT FROM AUTHOR]

X-ray microbeam radiotherapy can potentially widen the therapeutic window due to a geometrical redistribution of the dose. However, high requirements on photon flux, beam collimation, and system stability restrict its application mainly to large-scale, cost-intensive synchrotron facilities. With a unique laser-based Compact Light Source using inverse Compton scattering, we investigated the translation of this promising radiotherapy technique to a machine of future clinical relevance. We performed in vitro colony-forming assays and chromosome aberration tests in normal tissue cells after microbeam irradiation compared to homogeneous irradiation at the same mean dose using 25 keV X-rays. The microplanar pattern was achieved with a tungsten slit array of 50 μm slit size and a spacing of 350 μm. Applying microbeams significantly increased cell survival for a mean dose above 2 Gy, which indicates fewer normal tissue complications. The observation of significantly less chromosome aberrations suggests a lower risk of second cancer development. Our findings provide valuable insight into the mechanisms of microbeam radiotherapy and prove its applicability at a compact synchrotron, which contributes to its future clinical translation. [ABSTRACT FROM AUTHOR]