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The enrichment measurement of 235U is an important issue in the applications of nuclear material accounting and nuclear nonproliferation etc. The nondestructive assay (NDA) method based enrichment meter principle is a robust and direct measuring approach. At the same time, there are some limits, such as the infinite thickness approximation condition and the wall thickness correction, in comparison with the self-calibration relative ratio methods. According to the Klein–Nishina equation, the small-angle Compton scattering events can be used to estimate the attenuation due to the intervening matter between uranium material and gamma spectrometer. At State Nuclear Security Technology Center (SNSTC) we used three high-enrichment U 3 O 8 samples to perform the 235U enrichment measurement experiment by the enrichment meter approach. When shielding plates of iron are added, the measurement results deviate further from the certified value as the shield increases. Employing the small-angle Compton scattering events to estimate the attenuation, we accomplished the thickness correction for the iron-plate shield varying from one layer to four layers (with each thickness of 3.1 mm). • The shield thickness was extracted from the spectrum of uranium gamma rays. • The nonzero intercept implying detector window and dead layer was estimated. • The measured enrichment is corrected successfully by the estimated shield thickness. • The calibration method is presented for the shield thickness estimation. [ABSTRACT FROM AUTHOR]

We evaluated the applicability of neutron activation analysis for investigating the potential mobility of 90Sr in a pasture area in Hungary. To measure strontium concentrations, we made use of the 84Sr(n,γ)85Sr radiative capture reaction using neutron activation analysis and performed gamma spectroscopy using Compton-suppression techniques on the resulting 514.0 keV gamma ray. Our values for soil-to-plant transfer factors value of 1.6 (2.2) kg kg−1 were in agreement with recommended values from the ICRP and IAEA, as well as similar studies performed by independent researchers. Our values for plant-to-animal transfer coefficients and concentration ratios varied from suggested values by several orders of magnitude to agreement with other values. Based on our results the utilized transfer of stable strontium could not be regarded as a convenient substitute to help clarify the long-term transfer of radioactive strontium in the environment, because short term dosing was applied. Neutron activation analysis provides a unique niche as a technique with very little chemical processing and short sample analysis times. • Compton-suppression NAA offers a reliable method for the determination of stable strontium as a surrogate for 90Sr. • Short-term dosing with 90Sr gives non-steady-state TC (plant-to-animal transfer coefficient(s) and concentration ratio (CR). [ABSTRACT FROM AUTHOR]

• The present work is employing Compton scattering technique is aimed for the following objectives. • Radiation interaction parameters such as mass attenuation coefficient, effective atomic number, HVL, MFP, Electron density and CT number. • Comparison of experimental data with the theoretical data available on WinXcom. • Variation of radiation interaction parameters for Ce(NO 3) 3.6H 2 O solution for various concentrations at different Compton scattered energies. The objective of the present work is to assign radiation interaction parameters to the solutions of cerium (III) nitrate hexahydrate [(Ce(NO 3) 3.6H 2 O)] in different concentrations dissolved in acetone [(CH3) 2 CO]. The photons scattered from cylindrical aluminum target result in secondary photon beam of desired energy and were detected using 2″ × 2″ NaI(Tl) scintillation spectrometer. The results show a decrease in mass attenuation coefficient (μ m), effective atomic number (Z eff) and Electron density (N el) with the increasing gamma photon energies and decreasing concentrations. The values of Computed tomography (CT) number, interpreters of CT scan, are found to be increasing linearly with increase in concentration and exponentially with increase in Z eff. These results show a good agreement with the theoretical values obtained from WinXCom. [ABSTRACT FROM AUTHOR]

A scheme for generating gamma photons from laser interaction with a hollow-tube target filled with near-critical-density plasma is investigated using quantum electrodynamics particle-in-cell simulation. The solid-density tube wall stabilizes the laser propagation in the tube, guides the laser-accelerated relativistic electrons, and its endplate reflects the laser light. As the electrons collide head-on with the reflected laser, a large number of MeV gamma photons are generated through inverse Compton scattering. It is found that bright gamma radiation with power up to 1.4 PW and 37% laser-to-gamma ray energy conversion efficiency can be obtained with 5 × 1022 W cm–2 laser pulse. [ABSTRACT FROM AUTHOR]

In most high-resolution PET detector designs, there is an inherent trade-off between spatial resolution and detector efficiency. We have developed and tested a new geometry for the detector module which avoids this trade-off. The module uses a layered structure, in which four crystal slabs are stacked in the depth direction and optically separated by enhanced specular reflector (ESR) film. The scintillation light within each layer is measured by 16 SiPMs located on the four sides of the crystal. Analog signals from all SiPMs (4  ×  16) on the four sides of the crystal are digitized individually using a 64-channel TOFPET-2 module. The four-sided readout method reduces the problem of light trapping resulting from total internal reflection when reading out the end(s) of traditional scintillation crystal arrays, thus increasing the light collection efficiency. In this work, we demonstrate the readout of a complete layered detector with 4 layers. The high light collection efficiency results in a FWHM energy resolution of 10.3%, and a FWHM timing resolution of 348 ps. The distribution of scintillation light detected by the SiPMs was used to decode the interaction position of each gamma ray using a trained neural network. A FWHM spatial resolution of 1.1  ±  0.1 mm was achieved. This design allows the detection efficiency of the module to be increased by adding additional crystal slabs along the depth direction. Since the position, energy, and timing are measured for each layer independently, increasing the system sensitivity by adding more layers will not affect the spatial/energy/timing resolution. Furthermore, the layered structure allows partial recovery of position information for events that undergo Compton scatter within the detector. [ABSTRACT FROM AUTHOR]

A relativistic electron–positron pair beam can be produced in the interaction between TeV photons from a blazar and extragalactic background light. The relativistic e± pairs lose energy through inverse-Compton scattering (ICS) photons of the cosmic microwave background or plasma instabilities. The dominant energy-loss process is under debate. Based on the assumption that the dominant energy-loss process is ICS, the resulting cascade GeV radiation is usually used to constrain the intergalactic magnetic field (IGMF). Here, we include the energy-loss due to plasma oblique instability in the calculation of cascade gamma-ray flux, and investigate the impact of the plasma instability on the constraint of IGMF. Up-to-date GeV data and archival TeV data of the blazar 1ES 0229+200 are used. The results indicate that even if the oblique instability cooling is dominating ICS cooling, the cascade flux could still be used to constrain the IGMF. It is found that with the ratio between the cooling rates of the oblique instability and the ICS varying from 0.1,1 to 10, the lower limit of the IGMF of the cascade flux and the gamma-ray data changes from 8 × 10−18 G, 5 × 10−18 G to 10−18 G. If the ratio between the two cooling rates is 30, the estimate of IGMF based on the cascade flux is invalid. [ABSTRACT FROM AUTHOR]

Terrestrial Gamma-ray Flashes (TGFs) are short (< 2 ms) flashes of high energy (< 30 MeV) photons, produced by thunderstorms, between 10 and 15 km altitude (at least for TGFs detectable from space). They deposit a large amount of energy into the atmosphere and the ionosphere, since a large fraction (typically > 98%) of the initial source of high energy photons is absorbed before reaching space. When interacting with the atmosphere, the photons can produce a large quantity of electrons (through Compton scattering and pair production) and positrons (through pair production), but only a small fraction is able to escape the atmosphere [1,2].The surviving electrons and positrons are then bounded to Earth's magnetic field lines and can travel large distances inside the ionosphere and the magnetosphere. They have an effect on the radiation belts that is yet to be quantified. This phenomenon is called a Terrestrial Electron Beam (TEB).In this presentation, we report the first TEB detected by the Atmosphere-Space Interactions Monitor (ASIM). This event happened on September 16th, 2018. The ASIM-MXGS detector recorded an unusually long TGF (> 4 ms), with a softer spectrum than what is typically recorded for TGF events. Further modeling using the MCPEP code [3] permitted to estimate a likely geographical position of the TGF producing the TEB, where we could find a WWLLN match within a very short time interval (<15 ms), corresponding to the parent lightning. Imaging from a GOES-R satellite shows that the source TGF was generated close to an overshooting top of a thunderstorm. Further modeling, using Geant4 simulation of the ASIM mass model, confirms that MXGS most likely detected bremsstrahlung photons generated by relativistic electrons interacting with material surrounding the detector.References:[1] J. R., Dwyer, B. W., Grefenstette and D. M. Smith. High-energy electron beams launched into space by thunderstorms. Geophysical Research Letters, 2008.[2] B. E. Carlson T. Gjesteland and N. Østgaard. Terrestrial gamma‐ray flash electron beam geometry, fluence, and detection frequency. Journal of Geophysical Research (Space Physics), 2011.[3] D. Sarria, P.-L. Blelly and F. Forme. MC-PEPTITA : A Monte Carlo model for Photon, Electron and Positron Tracking In Terrestrial Atmosphere - Application for a terrestrial gamma ray flash. Journal of Geophysical Research (Space Physics), 2015. [ABSTRACT FROM AUTHOR]

Measurements of solar-flare electron-bremsstrahlung X-rays are affected by Compton scattering in the solar atmosphere of the downward-directed radiation. Here we study how Compton-scattered and energy-degraded radiation from nuclear-deexcitation gamma-ray lines and continua affect the measurements of the gamma-ray radiation. Deexcitation-line photons with trajectories directed away from the Sun escape without significant interactions even for flares at the limb. We calculate the Compton-scattered component spectrum from downward-directed deexcitation lines for typical solar-flare accelerated-ion kinetic-energy spectra. The scattered component only a makes a significant contribution to the emerging spectrum at energies below ≈ 600 keV and is most prominent for flares occurring near the center of the solar disk. We study Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra obtained from the 28 October 2003 disk-centered flare when the electron-bremsstrahlung contribution was relatively weak. We find that inclusion of the scattered component does not significantly affect any of the derived flare parameters. This is true, in part, because the scattered component is not detectable over the significant RHESSI detector count continuum due to partial energy depositions of higher-energy solar photons. The scattered component may affect flare spectral measurements obtained with gamma-ray detectors having a more "diagonal" response. [ABSTRACT FROM AUTHOR]

Gamma-ray beams with a large angular momentum may affect astrophysical phenomena, which calls for appropriate earth-based experimental investigations. For this purpose, we investigate the generation of well-collimated γ-ray beams with a very large orbital angular momentum using nonlinear Compton scattering of a strong laser pulse of twisted photons at ultrarelativistic electrons. Angular momentum conservation among absorbed laser photons, quantum radiation, and electrons is numerically demonstrated in the quantum radiation-dominated regime. We point out that the angular momentum of the absorbed laser photons is not solely transferred to the emitted γ photons, but due to radiation reaction shared between the γ photons and interacting electrons. The efficiency of the angular momentum transfer is optimized with respect to the laser and electron beam parameters. The accompanying process of electron-positron pair production is furthermore shown to enhance the orbital angular momentum gained by the γ-ray beam. [ABSTRACT FROM AUTHOR]

The Compton scattering cross section from 4He has been measured with high statistical accuracy over a scattering angle range of 40°-159° using a quasimonoenergetic 61-MeV photon beam at the High Intensity Gamma-Ray Source. The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (αs and βs) of the nucleon. These data can be fit with the model using values of αs and βs that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from effective field theories and lattice quantum chromodynamics. [ABSTRACT FROM AUTHOR]

We report on a detailed analysis of the γ-ray light curve of NGC 1275 using the Fermi Large Area Telescope data accumulated during 2008–2017. Major γ-ray flares were observed in 2015 October and 2016 December/2017 January when the source reached a daily peak flux of , achieving a flux of within 3 hr, which corresponds to an apparent isotropic γ-ray luminosity of . The most rapid flare had an e-folding time as short as hr, which had never been previously observed for any radio galaxy in γ-ray band. Also, γ-ray spectral changes were observed during these flares: in the flux versus photon index plane, the spectral evolution follows correspondingly a counterclockwise and a clockwise loop inferred from the light curve generated by an adaptive binning method. On 2016 December 30 and 2017 January 1 the X-ray photon index softened () and the flux increased nearly ∼3 times as compared with the quiet state. The observed hour-scale variability suggests a very compact emission region (), implying that the observed emission is most likely produced in the subparsec-scale jet if the entire jet width is responsible for the emission. During the active periods, the γ-ray photon index hardened, shifting the peak of the high-energy spectral component to , making it difficult to explain the observed X-ray and γ-ray data in the standard one-zone synchrotron self-Compton model. [ABSTRACT FROM AUTHOR]

PSR B1259-63/LS2883 is a binary system composed of a pulsar and a Be star. The Be star has an equatorial circumstellar disk (CD). The Fermi satellite discovered unexpected gamma-ray flares around 30 days after the last two periastron passages. The origin of the flares remains puzzling. In this work, we explore the possibility that the GeV flares are consequences of inverse Compton scattering of soft photons by the pulsar wind. The soft photons are from an accretion disk around the pulsar, which is composed of the matter from the CD captured by the pulsar’s gravity at disk-crossing before the periastron. At the other disk-crossing after the periastron, the density of the CD is not high enough, so accretion is prevented by the pulsar wind shock. This model can reproduce the observed spectrum energy distributions and light curves satisfactorily. [ABSTRACT FROM AUTHOR]

We present the results of our broadband study of the γ-ray emitting narrow line Seyfert 1 (NLSy1) galaxy SBS 0846+513 (z = 0.585). This includes multiband flux variations, γ-ray spectral analysis, broadband spectral energy distribution (SED) modeling, and intranight optical variability (INOV) observations carried out over six nights between 2012 November and 2013 March using the 2 m Himalayan Chandra Telescope and the 1.3 m telescope at Devasthal, India. Multiple episodes of flaring activity are seen in the γ-ray light curve of the source which are also reflected in the observations at lower frequencies. A statistically significant curvature is noticed in the seven years averaged γ-ray spectrum, thus indicating its similarity with powerful flat spectrum radio quasars (FSRQs). Modeling the SEDs with a one-zone leptonic emission model hints that the optical UV spectrum is dominated by synchrotron radiation, whereas inverse Compton scattering of broad line region photons reproduces the γ-ray part of the SEDs. The source was found to be variable on all the six nights of optical observations with a variation of ∼0.3 mag within a single night, coinciding with a high γ-ray activity state. The observed large amplitude INOV clearly indicates the presence of a closely aligned beamed relativistic jet in SBS 0846+513. Our broadband study supports the recent claims in literature that γ-ray emitting NLSy1 galaxies are similar to blazars and constitute the low black hole mass counterparts to FSRQs. [ABSTRACT FROM AUTHOR]

Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which originate from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected a mere ∼30 persistent sources. It is in stark contrast with the ∼2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be helpful to reduce the background under conditions similar to those in space. Accordingly, the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below 1 × 10−12 erg cm−2 s−1 at 1 MeV. [ABSTRACT FROM AUTHOR]

We describe a hybrid free-electron laser (FEL)/inverse Compton scattering (ICS) system that can be operated at very high repetition rates and with higher average gamma-ray fluxes than possible from ICS systems driven by J/kHz laser systems. Also, since the FEL system can generate 100 mJ class photon pulses at UV wavelengths, the electron beam energy can be lower than for systems driven with ∼micron wavelength lasers for attaining gamma rays of similar energy. [ABSTRACT FROM AUTHOR]

The large-scale jet of quasar 3C 273 has been observed in radio to gamma-ray frequencies. Earlier the X-ray emission from knot A of this jet has been explained with inverse Compton scattering of the cosmic microwave background radiations by the shock accelerated relativistic electrons in the jet. More recently it has been shown that this mechanism overproduces the gamma-ray flux at GeV energy and violates the observational results from Fermi LAT. We have considered the synchrotron emission from a broken power-law spectrum of accelerated protons in the jet to explain the observed X-ray to gamma-ray flux from knot A. The two scenarios discussed in our work are (i) magnetic field is high, synchrotron energy loss time of the protons is shorter than their escape time from the knot region and the age of the jet and (ii) their escape time is shorter than their synchrotron energy loss time and the age of the jet. These scenarios can explain the observed photon spectrum well for moderate values of Doppler factor. The required jet luminosity is high ∼1046 erg s−1 in the first scenario and moderate ∼1045 erg s−1 in the second, which makes the second scenario more favourable. [ABSTRACT FROM PUBLISHER]

Journal of Physics B: Atomic, Molecular and Optical Physics is delighted to announce a forthcoming special issue on compact x-ray sources, to appear in the winter of 2014, and invites you to submit a paper. The potential for high-brilliance x- and gamma-ray sources driven by advanced, compact accelerators has gained increasing attention in recent years. These novel sources—sometimes dubbed ‘fifth generation sources’—will build on the revolutionary advance of the x-ray free-electron laser (FEL). New radiation sources of this type have widespread applications, including in ultra-fast imaging, diagnostic and therapeutic medicine, and studies of matter under extreme conditions. Rapid advances in compact accelerators and in FEL techniques make this an opportune moment to consider the opportunities which could be realized by bringing these two fields together. Further, the successful development of compact radiation sources driven by compact accelerators will be a significant milestone on the road to the development of high-gradient colliders able to operate at the frontiers of particle physics. Thus the time is right to publish a peer-reviewed collection of contributions concerning the state-of-the-art in: advanced and novel acceleration techniques; sophisticated physics at the frontier of FELs; and the underlying and enabling techniques of high brightness electron beam physics. Interdisciplinary research connecting two or more of these fields is also increasingly represented, as exemplified by entirely new concepts such as plasma based electron beam sources, and coherent imaging with fs-class electron beams. We hope that in producing this special edition of Journal of Physics B: Atomic, Molecular and Optical Physics (iopscience.iop.org/0953-4075/) we may help further a challenging mission and ongoing intellectual adventure: the harnessing of newly emergent, compact advanced accelerators to the creation of new, agile light sources with unprecedented capabilities. New schemes for compact accelerators: laser- and beam-driven plasma accelerators; dielectric laser accelerators; THz accelerators. Latest results for compact accelerators. Target design and staging of advanced accelerators. Advanced injection and phase space manipulation techniques. Novel diagnostics: single-shot measurement of sub-fs bunch duration; measurement of ultra-low emittance. Generation and characterization of incoherent radiation: betatron and undulator radiation; Thomson/Compton scattering sources, novel THz sources. Generation and characterization of coherent radiation. Novel FEL simulation techniques. Advances in simulations of novel accelerators: simulations of injection and acceleration processes; simulations of coherent and incoherent radiation sources; start-to-end simulations of fifth generation light sources. Novel undulator schemes. Novel laser drivers for laser-driven accelerators: high-repetition rate laser systems; high wall-plug efficiency systems. Applications of compact accelerators: imaging; radiography; medical applications; electron diffraction and microscopy. Please submit your article by 15 May 2014 (expected web publication: winter 2014); submissions received after this date will be considered for the journal, but may not be included in the special issue. [ABSTRACT FROM AUTHOR]

The spectral shape of radiation due to inverse Compton scattering is analyzed in the Thomson and the Klein-Nishina regime for electron distributions with exponential cutoff. We derive analytical, asymptotic expressions for the spectrum close to the maximum cutoff region. We consider monoenergetic, Planckian, and synchrotron photons as target photon fields. These approximations provide a direct link between the distribution of parent electrons and the upscattered spectrum at the cutoff region. [ABSTRACT FROM AUTHOR]

Recently, Fermi-LAT detected GeV emission during the X-ray flaring activity in GRB 100728A. We study various scenarios for its origin. The hard spectrum of the GeV emission favors the external inverse Compton (EIC) origin in which X-ray flare photons are up-scattered by relativistic electrons in the external forward shock. This EIC scenario, with anisotropic scattering effect taken into account, can reproduce the temporal and spectral properties of the GeV emission in GRB 100728A. [ABSTRACT FROM AUTHOR]

Abstract: An overview of linear and nonlinear Compton scattering is presented, along with a comparison with Thomson scattering. Two distinct processes play important roles in the nonlinear regime: multiphoton interactions, leading to the generation of harmonics; and radiation pressure, yielding a downshift of the radiated spectral features. These mechanisms, their influence on the source brightness, and different modeling strategies are also briefly discussed. [Copyright &y& Elsevier]

Abstract: A laser-Compton scattering system is a unique and useful gamma-ray-beam source. The laser-Compton scattering gamma ray generation was tested on a synchrotron radiation facility, “NewSUBARU” at Lasti/UH. Cw Nd:YVO laser (wavelength: , maximum power: 5W) was used in the experiments. Maximum energies of scattered gamma ray are 17.6 and 39.1MeV at the operating electron energy of 1 and 1.5GeV, respectively. Generated gamma-ray was measured and used in the shielding tunnel of 45cm thickness concrete wall. A scintillation detector (NaI) and Ge detector were used to measure the gamma-ray spectrum and the yield. A measured gamma-ray yield of is in agreement with calculation. A spatial distribution of gamma-ray and its dependence on a polarization of incident laser were measured using imaging plate (IP). Preliminary experiments of gamma-ray application were performed for a nuclear transmutation in the disposal of the radioactive nuclear waste and on a gamma-ray radiography for nondestructive testing of a thick subject. New radiation shielding for the gamma-ray beamline was designed for extracting the higher flux gamma-rays for application. Radiation leakage was calculated by EGS4 and MCNPX. The calculations of neutron transport are important for observation of fast neutron generated from a target sample irradiated by gamma-ray beam. [Copyright &y& Elsevier]