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Thomson scattering sources are known for generating quasi-monochromatic, high-brightness, and polarization-tunable X-rays, which are widely applied in fields such as fluorescence imaging, magnetic circular dichroism, and nuclear physics. In this paper, we present an experimental demonstration of polarization control at the Tsinghua Thomson scattering X-ray source (TTX) by adjusting the laser polarization. A specially designed Compton polarimeter is employed to effectively analyze the Degree of Linear Polarization (DoLP) of the X-rays produced at the TTX. Our results indicate that the DoLP of X-rays within a collecting angle of 1 / (3 γ) , where γ is the Lorentz factor of the relativistic electron, closely matches the DoLP of the laser. Furthermore, we demonstrate that the X-ray polarization can be continuously modulated from linear polarization to circular polarization by adjusting the laser polarization, which can significantly enhance the functionality and applicability of Thomson Scattering sources for scientific research. [ABSTRACT FROM AUTHOR]

The release of radioactive gas into the atmosphere can diffuse into large volumes of air downwind from the point of release. The extent of radioactivity can cover thousands of cubic meters of air. For such large volumes, the weather models used to predict the down-wind distribution of the plume and the radiation transport models used to predict the radiation reaching ground-level from the plume can take tens of hours of computer time on multi-node institutional High-Performance Computing facilities. In this paper we focus on the radiation transport aspect of plume modeling. We describe a phenomenological method for approximating the amounts of radiation that reach ground level from large volumes of a static radioactive plume that can be calculated on a stand-alone personal computer in much shorter computation times than those usually needed for such large volume evaluations. We refer to this method as the Density Scaling Approximation (DSA). Its ability to approximate ground-level count rates of large plumes comes from using a small-plume volume with a scaled-up value of air density to simulate the same number of scatterings that occur during transport in larger plume volumes at normal air density. We demonstrate the DSA by using a 100 m-diameter air-filled hemispherical dome geometry with a uniform volumetric activity of 135Xe gas throughout the air-filled volume. The DSA for a larger dome diameter is obtained by evaluating the 100 m dome with an air density scaled up by the linear ratio of the larger diameter to the 100 m diameter. We find that this approximation works well for dome diameters up to 1200 m – the largest diameter studied and a size more than sufficient for accounting for all the radiation from 135Xe. Moreover, most of our DSA results can be calculated over 500 times faster than corresponding full-sized geometry with normal air density. To help evaluate the accuracy of the DSA and gain insight into how well it can reproduce different regions of the spectra, we use three, easily understood regions of interest to compare the DSA results to the full-sized geometry at normal air density results. These regions are the full-energy peak, the region of single-Compton scattering, and the region of multiple-Compton scattering. We show how the dominance of the Compton scattering mechanism determines this division and thus provides insight into how Compton scattering is manifested in spectra from photon scattering through air in general, and how well the DSA approximation works. [ABSTRACT FROM AUTHOR]

The backscatter X-ray system makes an image by detecting scattered particles from an object in the opposite direction by Compton scattering. This system has the advantage of detecting drugs or explosives composed of organic substances. In this study, we developed a backscatter X-ray detection system. The 6-ch DAQ system is able to store acquired data for 50 μs as 8 bytes and the 6-ch high voltage power supply board provides adjustable power from 0 to 1600 V. Using this detection system, we varied the tube voltage from 80 to 160 kV and observed backscatter X-ray images of two plastic phantoms at 160 kV. The results indicate a need to optimize the speed of the collimator and data acquisition time of the DAQ system to improve image quality. The backscatter X-ray imaging technology exhibits high scalability, making it applicable not only to security screening but also for medical and industrial purposes. [ABSTRACT FROM AUTHOR]

A polarimeter was constructed to measure the longitudinal polarization of a spin-polarized electron beam at 5 and 7 MeV. The polarimeter takes advantage of Compton scattering between circularly polarized bremsstrahlung photons produced by a longitudinally polarized electron beam striking a copper radiator and the spin-polarized electrons orbiting the iron atoms of an analyzing magnet. This so-called Compton transmission polarimeter is compact and relatively inexpensive compared to Mott-scattering polarimeters because no spin manipulator is required. This work presents the design of the radiator, analyzing magnet, photon detector assembly, and data acquisition system of the Compton transmission polarimeter as well as beam commissioning results performed at the Upgraded Injector Test Facility at Jefferson Lab. [ABSTRACT FROM AUTHOR]

Automatic identification and quantification of γ -emitting radionuclides, taking into account spectral deformations due to γ -interactions in radioactive source surroundings, is a challenging task in the nuclear field. In that context, this paper presents a Machine Learning approach based on autoencoder that can learn a model for the spectral signatures of γ -emitters with variability. Training and test datasets were obtained by means of simulated γ -spectra computed with the Geant4 simulation code according to increasing material thicknesses (steel, lead). A novel hybrid unmixing algorithm combining a pretrained autoencoder is studied for joint estimation of spectral signatures and counting in the case of mixtures of four radionuclides (57Co, 60Co, 133Ba, 137Cs). The investigations were carried out to account for spectral deformations due to attenuation, Compton scattering and fluorescence at high and low statistics. This study demonstrates the validity of this novel hybrid approach combining Machine Learning and Maximum Likelihood for the automatic full-spectrum analysis of γ -spectra. • Hybrid γ -spectra unmixing algorithm combining Machine Learning and Maximum Likelihood. • Modeling of spectral signature deformations by autoencoder with limited data. • Geant4 simulations of spectral deformations due to physical effects. • Full-spectrum unmixing using autoencoder as a generative model of γ -spectra. • Joint estimation of spectral signatures and mixing weights for all radionuclides. [ABSTRACT FROM AUTHOR]

The Southern European Thomson back-scattering source for Applied Research (STAR) is a high-energy photon facility located on the campus of the University of Calabria (UniCal). The facility was designed for its first phase to operate with an electron and photon energy up to 85 MeV and 140 keV respectively. For the second phase of the project the energy of the electrons, and thereby the photons, would be increased up to 150 MeV and 350 keV respectively. The Italian Institute for Nuclear Physics (INFN) was awarded the project for installing, testing, and commissioning the energy upgrade of the electron beamline. In this article, we will outline the progress of this upgrade. In particular the completion of the site acceptance test of the RF system and the IT infrastructure combined with the control system software. [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]

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]

Compton scatter imaging (CSI) is a promising, noninvasive imaging technique; however, it is limited by its poor utilization of X-rays and its bad image signal-to-noise ratio (SNR). In this work, a novel method combining push-broom CSI with coded-aperture imaging was devised to improve the utilization of backscattered X-rays and the image SNR. Firstly, the principles of coded-aperture push-broom CSI are illustrated, and its various applications are discussed. Then, simulations of a point source and a line source are performed to validate its feasibility. It was discovered that the inherent coding noise trends for the mask and the antimask were the opposite of each other. Therefore, these coding noises could be offset by averaging the two. Furthermore, a system prototype was built to scan objects, such as point phantoms, line phantoms, character phantoms of "IHEP", and other typical samples. Compared with traditional push-broom CSI, this novel system obtained a better backscatter image with lower X-ray power and at a farther distance. This feature is important for system miniaturization and radiation dose reduction. Although optimizations should be considered in the future, this approach demonstrates useful application potential. • We devise a novel method of coded-aperture push-broom Compton scatter imaging. • It improves the utilization of backscattered X-rays and the image SNR. • It shows a potential for system miniaturization and radiation dose reduction. • Noises could be offset mostly by averaging results of mask and antimask. • Simulations and experiments support the method well. [ABSTRACT FROM AUTHOR]

The Latin American Giant Observatory (LAGO) is a ground-based observatory studying solar or high-energy astrophysics transient events. LAGO takes advantage of its distributed network of Water Cherenkov Detectors (WCDs) in Latin America as a tool to measure the secondary particle flux reaching the ground. These secondary particles are produced during the interaction between the modulated cosmic rays flux and the atmosphere. The LAGO WCDs are sensitive to secondary charged particles, high energy photons through pair creation and Compton scattering, and even neutrons thanks to, e.g., the deuteration of protons in the water volume. The pulse shape generated by these particles depends on several factors, such as the detector geometry, the water purity, the sensor response, or the reflectivity and diffusivity of the inner coating. Due to the decentralized nature of LAGO, these properties are different for each node. Additionally, the pulse shape depends on the convolution between the response of the central photomultiplier (PMT) to individual photons and the time distribution of the Cherenkov photons reaching the PMT. Typically, a WCD gives pulses with a sharp rise time (∼ 10 ns) and a longer decay time (∼ 70 ns). In this work, the WCD data used is acquired using the original LAGO data-acquisition system that digitizes pulses at a sampling rate of 40 MHz and 10 bits resolution on time windows of 400 ns. Here, we apply unsupervised machine learning techniques to find patterns in the WCDs data and subsequently create groups, through clustering, that can be used to provide particle separation. We use data acquired from an individual WCD, showing that density-based clustering algorithms are suitable for automatic particle separation producing good candidate groups. Improved separation would help LAGO to reconstruct in situ the properties of primary cosmic rays flux. These results open the possibility to deploy machine learning-based models in our distributed detection network for onboard data analysis as an operative prototype, allowing detectors to be installed at very remote sites. [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]

Abstract A two-phase argon detector has high discrimination power between electron recoil and nuclear recoil events based on the pulse shape discrimination and the ionization/scintillation ratio (S2/S1). This character is very suitable for the dark matter search to establish the low background experiment. However, the basic properties of S2/S1 of argon are not well known, as compared with xenon. We report the evaluation of S2/S1 properties with a two-phase detector at drift-fields of 0.2–3.0 kV/cm. Finally, the discrimination power against electron recoil background of S2/S1 is discussed. [ABSTRACT FROM AUTHOR]

Abstract The AXSIS project (Attosecond X-ray Science: Imaging and Spectroscopy) aims to develop a THz-driven compact X-ray source for applications e.g. in chemistry and biology by using ultrafast coherent diffraction imaging and spectroscopy. The key components of AXSIS are the THz-driven electron gun and THz-driven dielectric loaded linear accelerator as well as an inverse Compton scattering scheme for the X-rays production. This paper is focused on the prototype of the THz-driven electron gun which is capable of accelerating electrons up to tens of keV. Such a gun was manufactured and tested at the test-stand at DESY. Due to variations in gun fabrication and generation of THz-fields the gun is not exactly operated at design parameters. Extended simulations have been performed to understand the experimentally observed performance of the gun. A detailed comparison between simulations and experimental measurements is presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract We present a status update on the dedicated R&D facility SINBAD which is currently under construction at DESY. The facility will host multiple independent experiments on the acceleration of ultra-short electron bunches and novel, high gradient acceleration methods. The first experiment is the ARES-experiment with a normal conducting 100 MeV S-band linac at its core. We present the objectives of this experiment ranging from the study of compression techniques to sub-fs level to its application as injector for various advanced acceleration schemes e.g. the plans to use ARES as a test-site for DLA experiments in the context of the ACHIP collaboration. The time-line including the planned extension with laser driven plasma-wakefield acceleration is presented. The second initial experiment is AXSIS which aims to accelerate fs-electron bunches to 15 MeV in a THz driven dielectric structure and subsequently create X-rays by inverse Compton scattering. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the design and simulation of a radiation detector system for diagnostic measurements of photon beams produced by Thomson or Compton Scattering. The photon beam is Compton scattered in a thin passive converter, and the resulting electrons are analyzed using a charge-coupled device-based tracker and classification algorithms. The flux of the scattered electrons is much lower than that of the photon beam and is additionally dispersed. This dispersal enables measurements while avoiding pileup, which is important in order to provide diagnostic information from intense ‘shot’ based pulsed systems, such as those being built to leverage laser wakefield accelerators. Simulations indicate that the designed system is capable of resolving beam parameters from a single shot. The fidelity to which various beam parameters can be resolved is presented as are methods that could result in further improvement to diagnostic resolution. [ABSTRACT FROM AUTHOR]

This paper presents X-ray spectra of channeling radiation expected at the FAST (Fermi Accelerator Science and Technology) facility in Fermilab. Our purpose is to produce high brightness quasi-monochromatic X-rays in an energy range from 40 keV to 110 keV. We will use a diamond crystal and low emittance electrons with an energy of around 43 MeV. The quality of emitted X-rays depends on parameters of the electron beam at the crystal. We present simulations of the beam optics for high brightness and high yield operations for a range of bunch charges. We estimate the X-ray spectra including bremsstrahlung background. We discuss how the electron beam distributions after the diamond crystal are affected by channeling. We discuss an X-ray detector system to avoid pile-up effects during high charge operations. [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]

We present a new experimental technique to perform self-absorption experiments in combination with nuclear resonance fluorescence using a quasi-monochromatic photon beam for the determination of absolute level widths of excited low-spin states. By measuring simultaneously at two target positions the amount of absorbed photon intensity is directly measured in a single experiment, which strongly reduces systematic uncertainties and reduces the amount of needed beam time by a factor of two. In addition the method does not rely on a given shape of the energy profile of the photon beam and, thus, can also be applied with quasi-monochromatic beams produced via Laser-Compton-Backscattering (LCB). Due to the strongly reduced background with these kind of photon beams this new method in combination with LCB promises a highly improved sensitivity for self-absorption experiments compared to experiments using bremsstrahlung. [ABSTRACT FROM AUTHOR]

A new Radial Time Projection Chamber (RTPC) was developed at the Jefferson Laboratory to track low-energy nuclear recoils to measure exclusive nuclear reactions, such as coherent deeply virtual Compton scattering and coherent meson production off 4 He. In 2009, we carried out these measurements using the CEBAF Large Acceptance Spectrometer (CLAS) supplemented by the RTPC positioned directly around a gaseous 4 He target, allowing a detection threshold as low as 12 MeV for 4 He. This article discusses the design, principle of operation, calibration methods and performances of this RTPC. [ABSTRACT FROM AUTHOR]

The ELI-NP facility (Extreme Light Infrastructure-Nuclear Physics) will deliver an intense and almost monochromatic gamma beam for frontier research in nuclear physics. Peculiar devices and techniques have been developed to measure and monitor the beam parameters during the commissioning and the operational phase. In this work we will present the Compton Spectrometer, designed to reconstruct the γ beam energy spectrum, by measuring the energy and the position of Compton scattered electrons. The energy and the angle of the scattered electron are measured by a High Purity Germanium detector and a double sided silicon strip detector. The associated photon is detected in coincidence with the electron by barium fluoride (BaF 2) crystals for trigger purpose. In this work we report the status of the characterization carried out on the detectors composing the spectrometer. • Compton spectrometer, designed to reconstruct the ELI-NP γ beam energy spectrum. • Energy of the scattered e − measured with a High Purity Germanium detector. • Scattered angle determined by a double sided silicon strip detector. • Scattered photon detected in coincidence by BaF 2 crystals for trigger purpose. • Tests carried out on the components of the spectrometer are presented. [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]

The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong 2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Compton imaging has been used for various applications including astronomical observations, radioactive waste management, and biomedical imaging. The positions of radioisotopes are determined in the intersections of multiple cone traces through a large number of events, which reduces signal to noise ratio (SNR) of the images. We have developed an advanced Compton imaging method to localize radioisotopes with high SNR by using information of the interactions of Compton scattering caused by two gamma rays at the same time, as the double photon coincidence Compton imaging method. The targeted radioisotopes of this imaging method are specific nuclides that emit several gamma rays at the same time such as 60 Co, 134 Cs, and 111 In, etc. Since their locations are determined in the intersections of two Compton cones, the most of cone traces would disappear in the three-dimensional space, which enhances the SNR and angular resolution. In this paper, the comparison of the double photon coincidence Compton imaging method and the single photon Compton imaging method was conducted by using GEANT4 Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

We present the design of a photon–photon collider based on conventional Compton gamma sources for the observation of secondary γ γ production. Two symmetric electron beams, generated by photocathodes and accelerated in linacs, produce two primary gamma rays through Compton back scattering with two high energy lasers. Tuning the system energy to the energy of the photon–photon cross section maximum, a flux of secondary gamma photons is generated. The process is analyzed by start-to-end simulations from the photocathodes to the propagation of the QED photons towards the detector. The new Monte Carlo code ‘Rate Of Scattering Events’ (ROSE) has been developed ad hoc for the counting of the QED events. Realistic numbers of the secondary gamma yield, referring to existing or approved set-ups and a discussion of the feasibility of the experiment are presented. [ABSTRACT FROM AUTHOR]

Silicon drift detectors have been successfully employed in both soft and hard X-ray spectroscopy. The response function to incident radiation at soft X-ray levels has been well studied and modeled, but less research has been published on response functions for these detectors to hard X-ray input spectra above 20 keV. When used with hard X-ray sources a significant low energy, non-peak response exists which can adversely affect detection limits for lighter elements in, for example, X-ray fluorescence spectroscopy. We present a numerical model that explains the non-peak response function of silicon drift detectors to hard X-rays based on incoherent Compton scattering within the detector volume. Experimental results are presented and numerically compared to model results. [ABSTRACT FROM AUTHOR]

Wilhelm and Jovanovic (2022) complained that a Monte–Carlo code for inverse Compton scattering is too slow. Fast codes are discussed. [ABSTRACT FROM AUTHOR]

Intense, quasi-monochromatic, polarized γ -ray beams with high and tunable energy produced by Compton scattering of laser photons against relativistic electrons are used for fundamental studies and applications. Following a series of photoneutron cross section measurements in the Giant Dipole Resonance (GDR) energy region performed at the NewSUBARU synchrotron radiation facility, we have developed the eliLaBr Monte Carlo simulation code for characterization of the scattered γ -ray photon beams. The code is implemented using Geant4 and is available on the GitHub repository (https://github.com/dan-mihai-filipescu/eliLaBr). Here we report the validation of the eliLaBr code on NewSUBARU LCS γ -ray beam flux and spectral distribution data and two applications performed with it for asymmetric transverse emittance profiles electron beams, characteristic for synchrotrons. The first application is based on a systematic investigation of transverse collimator offsets relative to the laser and electron beam axis. We show that the maximum energy of the LCS γ -ray beam is altered by vertical collimator offsets, where the edge shifts towards lower energies with the increase in the offset. Secondly, using the eliLaBr code, we investigate the effect of the laser polarization plane orientation on the properties of the LCS γ -ray beams produced with asymmetric emittance electron beams. We show that: 1. The use of vertically polarized lasers contributes to the preservation of the LCS γ -ray beam maximum energy edge by increasing the precision in the vertical collimator alignment. 2. Under identical conditions for the electron and laser beams phase-space distributions, the energy spectrum of the scattered LCS γ -ray beam changes with the laser beam polarization plane orientation. More precisely, the use of vertically polarized laser beams slightly deteriorates the LCS γ -ray beam energy resolution. [ABSTRACT FROM AUTHOR]

Positron emission particle tracking (PEPT) is used to study a wide range of scientific, industrial, and biomedical systems, typically those inaccessible through conventional optical particle tracking techniques. However, in dense or thick-walled systems a fraction of the coincident gamma-rays emitted from a PEPT tracer, called Lines-of-Response (LoRs), are attenuated via Compton scattering. Additionally, at high source activity, random LoRs may be formed by two unrelated events. The incorporation of scattered or random LoRs decreases PEPT spatial accuracy and can distort the trajectory. In this work, we use validation experiments and simulations to investigate the spatial accuracy of the Birmingham Method (BM) PEPT algorithm when two key free parameters are changed: the total number of LoRs in the sample and the fraction of LoRs in the sample used to locate the tracer. Our results show that the default algorithm parameters are not suitable for all cases, however, Monte Carlo simulations of PEPT experiments can be used to estimate the optimal parameter values. Ultimately a variant of the BM, called Dynamic-BM, is demonstrated in a virtual PEPT experiment. Dynamic-BM uses the optimal parameters on a sample-by-sample basis improving PEPT accuracy in this case by 4.03% over the best constant parameters and 76.5% over the default parameters. These improvements make PEPT a more accurate and thus more useful tool. • Two key free parameters a PEPT algorithm are optimised for spatial accuracy. • Optimal parameter values are discovered through experiments and simulations of PEPT. • The Birmingham Method is extended to dynamically change parameter values. • Using optimal values, spatial errors decrease by 76.5% compared to default values. [ABSTRACT FROM AUTHOR]

A cryostat was constructed for high-resolution X-ray Compton scattering measurements at temperature down to 1.7 K, in order to investigate superfluid helium-4. Compton profiles of helium were measured using synchrotron X-rays for gas and liquid phases, respectively. In the measurement of the liquid phase, we succeeded in measuring the Compton profile of the superfluid helium at 1.7 K. Comparison of the results with theoretical calculation reveals importance of many-body effects beyond the mean-field treatment of electron systems. [ABSTRACT FROM AUTHOR]

Polarimetric observations of celestial sources in the hard X-ray band stand to provide new information on emission mechanisms and source geometries. PoGO+ is a Compton scattering polarimeter (20–150 keV) optimised for the observation of the Crab (pulsar and wind nebula) and Cygnus X-1 (black hole binary), from a stratospheric balloon-borne platform launched from the Esrange Space Centre in summer 2016. Prior to flight, the response of the polarimeter has been studied with polarised and unpolarised X-rays allowing a Geant4-based simulation model to be validated. The expected modulation factor for Crab observations is found to be M Crab = ( 41.75 ± 0.85 ) % , resulting in an expected Minimum Detectable Polarisation (MDP) of 7.3% for a 7 day flight. This will allow a measurement of the Crab polarisation parameters with at least 5 σ statistical significance assuming a polarisation fraction ∼ 20 % – a significant improvement over the PoGOLite Pathfinder mission which flew in 2013 and from which the PoGO+ design is developed. [ABSTRACT FROM AUTHOR]

Many research and applications areas require photon sources capable of producing gamma-ray beams in the multi-MeV energy range with reasonably high fluxes and compact footprints. Besides industrial, nuclear physics and security applications, a considerable interest comes from the possibility to assess the state of conservation of cultural assets like statues, columns etc., via visualization and analysis techniques using high energy photon beams. Computed Tomography scans, widely adopted in medicine at lower photon energies, presently provide high quality three-dimensional imaging in industry and museums. We explore the feasibility of a compact source of quasi-monochromatic, multi-MeV gamma-rays based on Inverse Compton Scattering (ICS) from a high intensity ultra-violet (UV) beam generated in a free-electron laser by the electron beam itself. This scheme introduces a stronger relationship between the energy of the scattered photons and that of the electron beam, resulting in a device much more compact than a classic ICS for a given scattered energy. The same electron beam is used to produce gamma-rays in the 10-20 MeV range and UV radiation in the 10-15 eV range, in a ~4x22 m² footprint system. [ABSTRACT FROM AUTHOR]

The processes of the nonlinear Compton and the nonlinear Thomson scattering in a field of intense plane electromagnetic wave in terms of photon yield have been considered. The quantum consideration of the Compton scattering process allows us to calculate the probability of a few successive collisions k of an electron with laser photons accompanied by the absorption of n photons (nonlinear regime) when the number of collisions and the number of absorbed photons are of random quantities. The photon spectrum of the nonlinear Thomson scattering process was obtained from the classical formula for intensity using the Planck's law. The conditions for which the difference between the classical and the quantum regimes is manifested was obtained. Such a condition is determined by a discrete quantum radiation mechanism, namely, by the mean number of photons k ¯ emitted by an electron passing through the laser pulse. [ABSTRACT FROM AUTHOR]

We propose a time-of-flight (TOF) technique using plastic scintillators which have fast decay time of a few ns for positron emission tomography (PET). While the photoelectric absorption probability of the plastic for 511 keV gamma rays are extremely low due to its small density and effective atomic number, the cross section of Compton scattering is comparable to that of absorption by conventional inorganic scintillators. We thus propose TOF-PET using Compton scattering with plastic scintillators (Compton-PET), and performed fundamental experiments towards exploration of the Compton-PET capability. We demonstrated that the plastic scintillators achieved the better time resolution in comparison to LYSO(Ce) and GAGG(Ce) scintillators. In addition we evaluated the depth-of-interaction resolving capability with the plastic scintillators. [ABSTRACT FROM AUTHOR]

Image-guided surgery (IGS) is performed using a real-time surgery navigation system with three-dimensional (3D) position tracking of surgical tools. IGS is fast becoming an important technology for high-precision laparoscopic surgeries, in which the field of view is limited. In particular, recent developments in intraoperative imaging using radioactive biomarkers may enable advanced IGS for supporting malignant tumor removal surgery. In this light, we develop a novel intraoperative probe with a Compton camera and a position tracking system for performing real-time radiation-guided surgery. A prototype probe consisting of Ce : Gd 3 Al 2 Ga 3 O 12 (GAGG) crystals and silicon photomultipliers was fabricated, and its reconstruction algorithm was optimized to enable real-time position tracking. The results demonstrated the visualization capability of the radiation source with ARM = ∼ 22.1 ° and the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

The PREX-2 and CREX experiments in Hall A at Jefferson Lab are precision measurements of parity violating elastic electron scattering from complex nuclei. One requirement was that the incident electron beam polarization, typically ≈ 90 % , be known with 1% precision. We commissioned and operated a Møller polarimeter on the beam line that exceeds this requirement, achieving a precision of 0.89% for PREX-2, and 0.85% for CREX. The uncertainty is purely systematic, accumulated from several different sources, but dominated by our knowledge of the target polarization. Our analysis also demonstrates the need for accurate atomic wave functions in order to correct for the Levchuk Effect. We describe the details of the polarimeter operation and analysis, as well as (for CREX) a comparison to results from a different polarimeter based on Compton scattering. [ABSTRACT FROM AUTHOR]

We have developed a cryogenic target for use at the High Intensity γ -ray Source (HI γ S). The target system is able to liquefy 4 He at 4 K, hydrogen at 20 K, and deuterium at 23 K to fill a 0.3 L Kapton cell. Liquid temperatures and condenser pressures are recorded throughout each run in order to ensure that the target's areal density is known to ∼ 1 %. The target is being utilized in a series of experiments which probe the electromagnetic polarizabilities of the nucleon. [ABSTRACT FROM AUTHOR]

Over the last two decades, BNL׳s ATF has pioneered the use of high-peak power CO 2 lasers for research in advanced accelerators and radiation sources. Our recent developments in ion acceleration, Compton scattering, and IFELs have further underscored the benefits from expanding the landscape of strong-field laser interactions deeper into the mid-infrared (MIR) range of wavelengths. This extension validates our ongoing efforts in advancing CO 2 laser technology, which we report here. Our next-generation, multi-terawatt, femtosecond CO 2 laser will open new opportunities for studying ultra-relativistic laser interactions with plasma in the MIR spectral domain, including new regimes in the particle acceleration of ions and electrons. [ABSTRACT FROM AUTHOR]

The ELI-NP Gamma Beam Source (GBS) is now under construction in Magurele–Bucharest (RO). Here an advanced source of gamma photons with unprecedented specifications of brilliance ( > 10 21 ), monochromaticity (0.5%) and energy tunability (0.2–19.5 MeV) is being built, based on Inverse Compton Scattering in the head-on configuration between an electron beam of maximum energy 750 MeV and a high quality high power ps laser beam. These requirements make the ELI-NP GBS an advanced and challenging gamma ray source. The electron beam dynamics analysis and control regarding the machine sensitivity to the possible jitter and misalignments are presented. The effects on the beam quality are illustrated providing the basis for the alignment procedure and jitter tolerances. [ABSTRACT FROM AUTHOR]

Detection of γ -ray polarization in Positron Emission Tomography (PET) is as yet an unexploited feature that could be used as an additional handle to improve signal-to-background ratio in this imaging modality. The γ polarization is related to the azimuthal angle in the Compton scattering process, so the initial correlation of polarizations of the annihilation quanta translates to the correlation of the azimuthal angles in events where both annihilation photons undergo Compton scattering in respective detectors. This results in a modulated distribution of the azimuthal angle difference for true events, while this modulation is lacking for the background events. We present a comprehensive experimental study of five detector configurations based on scintillator matrices and silicon photomultipliers, suitable for measuring the azimuthal modulation. The modules consist of either GaGG:Ce or LYSO:Ce pixels with sizes varying from 1. 9 × 1. 9 × 20 mm 3 to 3 × 3 × 20 mm 3. The distinctive feature of the modules is that they can reconstruct the Compton scattering by detecting the recoil electron and the scattered γ in a single detector layer, which simplifies extension to larger systems. The amplitude modulation of the azimuthal angles' difference is clearly observable in all configurations ranging from 0. 26 ± 0. 01 to 0. 34 ± 0. 02 depending on the event selection criteria. The results suggest that finer detector segmentation plays a leading role in achieving higher modulation factors. [ABSTRACT FROM AUTHOR]

In this paper we present a method of scintillation detector energy calibration using the gamma-rays. The technique is based on the Compton scattering of gamma-rays in a scintillation detector and subsequent photoelectric absorption of the scattered photon in the Ge-detector. The novelty of this method is that the source of gamma rays, the germanium and scintillation detectors are immediately arranged adjacent to each other. The method presents an effective solution for the detectors consisting of a low atomic number materials, when the ratio between Compton effect and photoelectric absorption is large and the mean path of gamma-rays is comparable to the size of the detector. The technique can be used for the precision measurements of the scintillator light yield dependence on the electron energy. [ABSTRACT FROM AUTHOR]

The Rayleigh to Compton scattering ratio ( R / C ) is a very convenient parameter, which can be utilized in material analysis and estimating effective atomic number ( Z eff ). In the case for a relatively low scattering angle, for which the energy of the Compton scattered photons is not very much different from that of incident photons, the corrections due to self-absorption for Rayleigh and Compton scattering will be roughly equal. Therefore, it enables a result to be obtained which is almost independent of X-ray attenuation inside the sample and it will depend only on the material under investigation. The most frequently used method for calculation of Z eff available in literature is plotting R / C of elements as a function of atomic number and constituting the best fit curve. From this fit curve, the respective Z eff can be determined using R / C of the material. In the present study, we report Z eff of different materials using different methods such as interpolation and direct methods as possible alternatives to the most common fitting method. The results were compared with the experiments wherever possible. The agreement between interpolation method and the fitting method was found to be very satisfactory as relative changes (%) were always less than 9% while the direct method results with somehow significantly higher values of Z eff when compared to the other methods. [ABSTRACT FROM AUTHOR]

Analytical properties of Compton profiles are used in order to simplify the analysis of neutron Compton scattering experiments. In particular, the possibility to fit the difference of Compton profiles is discussed as a way to greatly decrease the level of complexity of the data treatment, making the analysis easier, faster and more robust. In the context of the novel method proposed, two mathematical models describing the shapes of differenced Compton profiles are discussed: the simple Gaussian approximation for harmonic and isotropic local potential, and an analytical Gauss–Hermite expansion for an anharmonic or anisotropic potential. The method is applied to data collected by VESUVIO spectrometer at ISIS neutron and muon pulsed source (UK) on Copper and Aluminium samples at ambient and low temperatures. [ABSTRACT FROM AUTHOR]

Stochastic image reconstruction has been applied to a dual-particle imaging system being designed for nuclear safeguards applications. The dual-particle imager (DPI) is a combined Compton-scatter and neutron-scatter camera capable of producing separate neutron and photon images. The stochastic origin ensembles (SOE) method was investigated as an imaging method for the DPI because only a minimal estimation of system response is required to produce images with quality that is comparable to common maximum-likelihood methods. This work contains neutron and photon SOE image reconstructions for a 252 Cf point source, two mixed-oxide (MOX) fuel canisters representing point sources, and the MOX fuel canisters representing a distributed source. Simulation of the DPI using MCNPX-PoliMi is validated by comparison of simulated and measured results. Because image quality is dependent on the number of counts and iterations used, the relationship between these quantities is investigated. [ABSTRACT FROM AUTHOR]

We compute the average polarisation asymmetry from the Klein–Nishina differential cross-section on free electrons at rest. As expected from the expression for the asymmetry, the average asymmetry is found to decrease like the inverse of the incident photon energy asymptotically at high energy. We then compute a simple estimator of the polarisation fraction that makes optimal use of all the kinematic information present in an event final state, by the use of “moments” method, and we compare its statistical power to that of a simple fit of the azimuthal distribution. In contrast to polarimetry with pair creation, for which we obtained an improvement by a factor of larger than two in a previous work, here for Compton scattering the improvement is only of 10–20%. [ABSTRACT FROM AUTHOR]

This study evaluated the use of Compton imaging technology to monitor prompt gamma rays emitted by 10 B in boron neutron capture therapy (BNCT) applied to a computerized human phantom. The Monte Carlo method, including particle-tracking techniques, was used for simulation. The distribution of prompt gamma rays emitted by the phantom during irradiation with neutron beams is closely associated with the distribution of the boron in the phantom. Maximum likelihood expectation maximization (MLEM) method was applied to the information obtained from the detected prompt gamma rays to reconstruct the distribution of the tumor including the boron uptake regions (BURs). The reconstructed Compton images of the prompt gamma rays were combined with the cross-sectional images of the human phantom. Quantitative analysis of the intensity curves showed that all combined images matched the predetermined conditions of the simulation. The tumors including the BURs were distinguishable if they were more than 2 cm apart. [ABSTRACT FROM AUTHOR]

A dual-particle imaging (DPI) system, capable of simultaneously imaging fast neutrons and gamma rays, has been operated in the presence of mixed-oxide (MOX) fuel to assess the system׳s angular resolution and material-characterization capabilities. The detection principle is based on the scattering physics of neutrons (elastic scattering) and gamma rays (Compton scattering) in organic and inorganic scintillators. The detection system is designed as a combination of a two-plane Compton camera and a neutron-scatter camera. The front plane consists of EJ-309 liquid scintillators and the back plane consists of interleaved EJ-309 and NaI(Tl) scintillators. MCNPX-PoliMi was used to optimize the geometry of the system and the resulting prototype was built and tested using a Cf-252 source as an SNM surrogate. A software package was developed to acquire and process data in real time. The software was used for a measurement campaign to assess the angular resolution of the imaging system with MOX samples. Measurements of two MOX canisters of similar isotopics and intensity were performed for 6 different canister separations (from 5° to 30°, corresponding to distances of 21 cm and 131 cm, respectively). The measurements yielded a minimum separation of 20° at 2.5 m (86-cm separation) required to see 2 separate hot spots. Additionally, the results displayed good agreement with MCNPX-PoliMi simulations. These results indicate an angular resolution between 15° and 20°, given the 5° step. Coupled with its large field of view, and its capability to differentiate between spontaneous fission and (α,n) sources, the DPI system shows its potential for nuclear-nonproliferation applications. [ABSTRACT FROM AUTHOR]

We have constructed a new laser-Compton-scattering facility, called the LEPS2 beamline, at the 8 GeV electron storage ring, SPring-8. This facility provides a linearly polarized photon beam in a tagged energy range of 1.3–2.4 GeV. Thanks to a small divergence of the low-emittance storage-ring electrons, the tagged photon beam has a size (σ) suppressed to about 4 mm even after it travels about 130 m to the experimental building that is independent of the storage ring building and contains large detector systems. This beamline is designed to achieve a photon beam intensity higher than that of the first laser-Compton-scattering beamline at SPring-8 by adopting the simultaneous injection of up to four high-power laser beams and increasing a transmittance for the long photon-beam path up to about 77%. The new beamline is under operation for hadron photoproduction experiments. [ABSTRACT FROM AUTHOR]

We report here a theoretical proof of the limiting value of the velocity of target/particle responsible for various photon–electron interactions in the Compton scattering experiment which may be carried out in various applications such as gamma-ray spectroscopy. Compton scattering deals with the collision of photons with a target particle where both energy and momentum are transferred to the particle while the photon moves with reduced energy and a change of momentum. Here, the changed energy of a photon depends on the angle between the incident axis and scattered photon (θ), the rest mass of the electron, and the frequency of the photon before the collision. However, when some initial velocity is provided to an electron that is at rest initially, then in such cases, the particle obeys limiting value on velocity for a particular energetic photon to follow Compton scattering. In such cases, the changed frequency of photons also depends on the initial and final velocity of nonstationary electrons during a collision, including the angle (φ ′) between the recoil electron and incident axis. Here, we have presented the derivations to calculate the recoil velocity of the nonstationary electron. These terms are the accurate solution of the Compton shift. We have tried to calculate the upper limit or limiting values of the initial velocity of the target particle in Compton scattering. Further, we have computationally demonstrated that there is a dependence of scattered photon frequency on initial velocity of target particle (u) and mass of the target particle (m) at a higher scattering angle. Finally, numerical simulations were carried out with particles such as an electron, pion (+/-, 0) to verify the greater degree of accuracy of the particles in spectroscopic detectors such as gamma-ray spectroscopy and other high energy spectroscopic techniques. [ABSTRACT FROM AUTHOR]

We present a novel method to perform gamma-ray spectroscopy suitable for extreme pileup situations, wherein traditional pulse-height spectroscopy is infeasible or impractical. One example of such application is spectral characterization of intense laser-based radiation sources that employ laser wakefield acceleration, in which a large number of photons can be produced in a well-collimated beam on a picosecond or shorter timescale. The method relies on the angularly-resolved calorimetric measurement of Compton scattering. The probability for a photon to undergo Compton scattering into a given solid angle is a function of its energy and is described by the Klein–Nishina formula. By first Compton scattering the incident beam and then measuring the total energies deposited in multiple detectors placed at various scattering angles, the incident beam energy spectrum can be reconstructed without resolving the individual events in detectors. We compare the performance of an maximum likelihood expectation maximization algorithm with that of an artificial neural network to measure the energy spectrum of a beam of monoenergetic gamma rays from 137Cs decay. We demonstrate that the method can be used to reconstruct the characteristic inverse Compton scattering spectra. [ABSTRACT FROM AUTHOR]