Bremsstrahlung Photon Production Research Articles

Hard-photon production and its correlation with intermediate-mass fragments in a framework of a quantum molecular dynamics model

Hard photon provides a unique probe for nuclear reaction dynamics. In this work, we embedded incoherent neutron-proton bremsstrahlung photon production channel in a framework of isospin-dependent quantum molecular dynamics (IQMD) model and performed a systematic study of multiplicities of hard photons and intermediate-mass fragments (IMFs). It is found that the IQMD model with the in-medium nucleon-nucleon cross section can reproduce previous experimental data of hard-photon energy spectra better. By investigating the incident energy and centrality dependencies of multiplicities of hard photons and IMFs of $^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$ collisions, it is found that the multiplicity correlation between thermal photons and IMFs can provide valuable information on nuclear liquid-gas phase transition. Additionally, temperatures from the thermal emitting sources are also investigated. The results indicate that hard photons provide some unique information of the thermodynamical state of multifragmentating nuclear system.

X‐ray Signatures of Lightning‐Induced Electron Precipitation

AbstractWe present detailed numerical modeling to predict expected X‐ray signatures from lightning‐induced electron precipitation (LEP) events. Simulations include the transionospheric propagation of the lightning electromagnetic pulse; ray tracing through the magnetosphere, including Landau damping; wave‐particle interactions resulting in loss cone fluxes; and Monte Carlo simulation of the electron precipitation process, including bremsstrahlung photon production and propagation to a balloon observing platform. Modeling is included to show that our simulated events are consistent with subionospheric very low frequency observations of LEP. Simulations show that these events should be observable from balloon‐based platforms. The modeled LEP event signatures, including X‐ray flux, spectrum, and pulse shape, are then compared with observations of energetic X‐ray pulses from the Balloon Array for Radiation‐belt Relativistic Electron Losses 1U balloon taken in January 2013 and are shown to be highly consistent with the observations. The pulses were observed near , while the balloon was off the coast of Antarctica at about 70°S, 5–20°W. Correlations with GOES imagery and global lightning data, together with analysis of the temporal and spectral signatures of these pulses, led to the initial suggestion that these events could be signatures of LEP. However, for only a fraction of these events could a causative lightning discharge be identified in global lightning data sets. This poor correlation may be partially attributed to causative strokes being missed by the global lightning networks; nonetheless, we discuss other possible explanations for these events.

Low-energy bremsstrahlung photon in relativistic nucleon+nucleon collisions

We study the production of bremsstrahlung photons in relativistic $\mathrm{nucleon}+\mathrm{nucleon}$ collisions by introducing a deceleration time of electromagnetic currents. It is found that the bremsstrahlung photon spectrum at low energy does not depend on the deceleration time, but solely on the amount of reduced electromagnetic current in collision. On the other hand, the photon spectrum becomes soft with increasing deceleration time. We also find that the bremsstrahlung photon spectrum in $p+n$ collisions is quite different from that in $p+p$ collisions at low energy.

Michel electron reconstruction using cosmic-ray data from the MicroBooNE LArTPC

The MicroBooNE liquid argon time projection chamber (LArTPC) has been taking data at Fermilab since 2015 collecting, in addition to neutrino beam, cosmic-ray muons. Results are presented on the reconstruction of Michel electrons produced by the decay at rest of cosmic-ray muons. Michel electrons are abundantly produced in the TPC, and given their well known energy spectrum can be used to study MicroBooNE's detector response to low-energy electrons (electrons with energies up to ~ 50 MeV). We describe the fully-automated algorithm developed to reconstruct Michel electrons, with which a sample of ~ 14,000 Michel electron candidates is obtained. Most of this article is dedicated to studying the impact of radiative photons produced by Michel electrons on the accuracy and resolution of their energy measurement. In this energy range, ionization and bremsstrahlung photon production contribute similarly to electron energy loss in argon, leading to a complex electron topology in the TPC. By profiling the performance of the reconstruction algorithm on simulation we show that the ability to identify and include energy deposited by radiative photons leads to a significant improvement in the energy measurement of low-energy electrons. The fractional energy resolution we measure improves from over 30% to ~ 20% when we attempt to include radiative photons in the reconstruction. These studies are relevant to a large number of analyses which aim to study neutrinos by measuring electrons produced by νe interactions over a broad energy range.

Neutron–proton bremsstrahlung as a possible probe of high-momentum component in nucleon momentum distribution

Abstract Neutron-proton bremsstrahlung in intermediate energy nucleus–nucleus collisions is proposed as a possible probe to study the high-momentum component in nucleon momentum distribution of finite nucleus. Based on the Boltzmann–Uehling–Uhlenbeck (BUU) transport model, the effects of high-momentum component on the production of bremsstrahlung photons in the reaction of C 12 + 12 C collisions at different incident beam energies are studied. It is found that the high-momentum component increases the high-energy bremsstrahlung photon production remarkably. Furthermore, the ratio of photon production at different incident beam energies is suggested as a potential observable to probe the high-momentum component in nucleon momentum distribution of finite nucleus.

Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4.

This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons Nγ/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ε). In addition, we present comparisons of GEANT4 simulations performed with a “standard” and a “low-energy” physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.Key PointsTesting the feedback mechanism with GEANT4Validating the GEANT4 programming toolkitStudy the ratio of bremsstrahlung photons to electrons at TGF source altitude

The impact of image reconstruction bias on PET/CT 90Y dosimetry after radioembolization.

PET/CT imaging after radioembolization is a viable method for determining the posttreatment (90)Y distribution in the liver. Low true-to-random coincidence ratios in (90)Y PET studies limit the quantitative accuracy of these studies when reconstruction algorithms optimized for traditional PET imaging are used. This study examined these quantitative limitations and assessed the feasibility of generating radiation dosimetry maps in liver regions with high and low (90)Y concentrations. (90)Y PET images were collected on a PET/CT scanner and iteratively reconstructed with the vendor-supplied reconstruction algorithm. PET studies on a Jaszczak cylindric phantom were performed to determine quantitative accuracy and minimum detectable concentration (MDC). (90)Y and (18)F point-source studies were used to investigate the possible increase in detected random coincidence events due to bremsstrahlung photons. Retrospective quantitative analyses were performed on (90)Y PET/CT images obtained after 65 right or left hepatic artery radioembolizations in 59 patients. Quantitative image errors were determined by comparing the measured image activity with the assayed (90)Y activity. PET images were converted to dose maps through convolution with voxel S values generated using MCNPX, a Monte Carlo N-particle transport code system for multiparticle and high-energy applications. Tumor and parenchyma doses and potential bias based on measurements found below the MDC were recorded. Random coincidences were found to increase in (90)Y acquisitions, compared with (18)F acquisitions, at similar positron emission rates because of bremsstrahlung photons. Positive bias was observed in all images. Quantitative accuracy was achieved for phantom inserts above the MDC of 1 MBq/mL. The mean dose to viable tumors was 183.6 ± 156.5 Gy, with an average potential bias of 3.3 ± 6.4 Gy. The mean dose to the parenchyma was 97.1 ± 22.1 Gy, with an average potential bias of 8.9 ± 4.9 Gy. The low signal-to-noise ratio caused by low positron emission rates and high bremsstrahlung photon production resulted in a positive bias on (90)Y PET images reconstructed with conventional iterative algorithms. However, quantitative accuracy was good at high activity concentrations, such as those found in tumor volumes, allowing for adequate tumor (90)Y PET/CT dosimetry after radioembolization.

Electron beam treatment verification using measured and Monte Carlo predicted portal images

Electron beam treatments may benefit from techniques to verify patient positioning and dose delivery. This is particularly so for complex techniques such as mixed photon and electron beam radiotherapy and electron beam modulated therapy. This study demonstrates that it is possible to use the bremsstrahlung photons in an electron beam from a dual scattering foil linear accelerator to obtain portal images of electron beam treatments. The possibility of using Monte Carlo (MC) simulations to predict the electron beam treatment portal images was explored. The MC code EGSnrc was used to model a Varian CL21EX linear accelerator (linac) and to characterize the bremsstrahlung photon production in the linac head. It was found that the main sources of photons in the electron beam are the scattering foils, the applicator and the beam-shaping cut-out. Images were acquired using the Varian CL21EX linac and the Varian aS500 electronic portal imager (EPI); four electron energies (6, 9, 12, 16 MeV), and different applicator and cut-out sizes were used. It was possible to acquire images with as little as 10.7 MU per image. The contrast, the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), the resolution and an estimate of the modulated transfer function (MTF) of the electron beam portal images were computed using a quality assurance (QA) phantom and were found to be comparable to those of a 6 MV photon beam. Images were also acquired using a Rando anthropomorphic phantom. MC simulations were used to model the aS500 EPID and to obtain predicted portal images of the QA and Rando phantom. The contrast in simulated and measured portal images agrees within ±5% for both the QA and the Rando phantom. The measured and simulated images allow for a verification of the phantom positioning by making sure that the structure edges are well aligned. This study suggests that the Varian aS500 portal imager can be used to obtain patient portal images of electron beams in the scattering foil linacs.

The radiation environment in and near high gradient rf cavities

Measurements of the X-ray flux, electron flux and spectrum are presented with the aim of evaluating the usefulness of ionization sensitive single particle detectors in the immediate environment of an rf cavity. The measured fluxes are found to be roughly consistent with field emission of electrons followed by one generation of bremsstrahlung photon production, with absorption and scattering of the final photons and electrons in the cavity and vacuum chamber structure.

Bremsstrahlung and photon production in thermal QCD

In this paper, we extend the study of bremsstrahlung photon production in a quark-gluon plasma to the cases of soft static photons and hard real photons. The general framework of this study is the effective perturbative expansion based on the resummation of hard thermal loops. Despite the fact that bremsstrahlung only comes at two loops, we find that in both cases it generates contributions of the same order of magnitude as those already calculated by several other groups at one loop. Furthermore, a new process contained in the two-loop diagrams dominate the emission of a very hard real photon. In all cases, the rate of real or virtual photon production in the plasma is appreciably increased compared to the one-loop predictions.

Gamma-Ray Transport Calculation Including Bremsstrahlung by Monte Carlo Code MORSE

Bremsstrahlung photon estimation was added to γ-ray transport calculation to improve the accuracy of neutron γ-ray coupled calculation. The validity of bremsstrahlung photon production calculation was examined numerically using a Monte Carlo code. Error due to neglect of electron multiple scattering was estimated, which showed the essential importance of effect of electron multiple scattering to estimation of bremsstrahlung photons in γ-ray transport calculation. To calculate electron multiple scattering in a simple way with sufficient accuracy, electrons are assumed to reach complete diffusion state prior to its bremsstrahlung photon emission. Electron angular distribution at its bremsstrahlung photon emission is assumed to be Gaussian distribution. Calculation by this method is compared with the experimental data, and the result of exact calculation. The validity of this method was shown by the agreement in sufficient accuracy between them. A Monte Carlo code MORSE-CG was improved to do all the numerical calculation of this work. The new code is called as MORSE-BREM.

Gamma-Ray Transport Calculation Including Bremsstrahlung by Monte Carlo Code MORSE.

Bremsstrahlung photon estimation was added to γ-ray transport calculation to improve the accuracy of neutron γ-ray coupled calculation. The validity of bremsstrahlung photon production calculation was examined numerically using a Monte Carlo code. Error due to neglect of electron multiple scattering was estimated, which showed the essential importance of effect of electron multiple scattering to estimation of bremsstrahlung photons in γ-ray transport calculation. To calculate electron multiple scattering in a simple way with sufficient accuracy, electrons are assumed to reach complete diffusion state prior to its bremsstrahlung photon emission. Electron angular distribution at its bremsstrahlung photon emission is assumed to be Gaussian distribution. Calculation by this method is compared with the experimental data, and the result of exact calculation. The validity of this method was shown by the agreement in sufficient accuracy between them. A Monte Carlo code MORSE-CG was improved to do all the numerica...

Monte Carlo Simulation of a New Gamma Ray Telescope

A new Monte Carlo code has been written to simulate the response of the new University of California double scatter gamma ray telescope. This package of modular software routines, written in VAX FORTRAN 77 simulates the detection of 0.1 to 35 MeV gamma rays. The new telescope is flown from high altitude balloons to measure medium energy gamma radiation from astronomical sources. This paper presents (1) the basic physics methods in the code (2) and the predicted response functions of the telescope. Gamma ray processes include Compton scattering, pair production and photoelectric absorption in plastic scintillator, NaI(Tl) and aluminum. Electron transport processes include ionization energy loss, multiple scattering, production of bremsstrahlung photons and positron annihilation.

Understanding thin film X‐ray spectra

SUMMARYFormulae suitable for predicting X‐ray production cross‐sections in thin foils are described. A modified Bethe‐Heitler equation seems well suited to describe the production of bremsstrahlung photons and, for fixed experimental conditions, may be expressed in a simple parametric form. Simple equations for calculating characteristic photon production are less satisfactory and the predictions of different formulae differ markedly. For microanalytical purposes, however, where relative rather than absolute cross‐sections are required, the differences become less pronounced. Finally, some uses for the cross‐sections in X‐ray microanalysis are considered.

Study of High-Energy Gamma Rays from Relativistic Nucleus-Nucleus Collisions

First measurements of 40-500-MeV $\ensuremath{\gamma}$ rays from collisions of 2-GeV/amu Ne and Ar with Ca and Pb targets are presented. Implications with regard to production of bremsstrahlung photons and of ${\ensuremath{\pi}}^{0}$, $\ensuremath{\eta}$, and $\ensuremath{\Delta}(1232)$ particles are discussed.

Spatial variation for flares observed with the gamma ray spectrometer aboard the SMM satellite

We have searched for anisotropic X-ray bremsstrahlung photon production from relativistic electrons by studying the heliocentric angular dependence of 53 flares detected at energies above 300 keV. We have found no evidence for a higher rate of detectable flares near the limb at the 80% confidence level. This result implies that the X-ray directivity as defined by the ratio of photon intensity at 75° and 0° of heliocentric angle is less than 1.5 above 300 keV and strongly rejects any flare model predicting X-ray production from a radial “beam” of energetic electrons.