Bremsstrahlung Production Research Articles

Low energy electron transport with EGS

The use of EGS, a general purpose Monte Carlo electron-photon transport system, has been investigated for low Z materials with incident electron energies as low as 50 keV while tracking electrons down to energies as low as 1 keV. It was found that: (1) the default electron step-size algorithm had to be modified, (2) care had to be taken to avoid turning off multiple scattering by using too short step-sizes; and (3) suitable cutoff energies for secondary electron production had to be used. Under these circumstances, it was found that for electron detector response functions and for electron transmission and reflection coefficients for slabs of material, EGS produces results which are in reasonable agreement with the calculated results of ETRAN and with experimental data. In the low Z cases investigated, no differences attributable to the different multiple scattering formalisms used in the two codes could be found although, as expected. EGS does predict too much bremsstrahlung production for electrons below 2 MeV kinetic energy because it ignores the Elwert correction factor. The straggling in the energy-loss distribution predicted by ETRAN using the Landau formalism was found to be in good agreement with the energy distribution calculated by EGS which includes energy-loss straggling by explicitly taking into account energy loss from random discrete events. A minor logic error was found in EGS when production of low energy secondary electrons was considered (less than 80 keV for water), although the observable effects were found to be small. Coding for a short routine to provide electron step-sizes of equal energy loss is presented.

Continuum x rays produced by light-ion—atom collisions

Radiative processes in light-ion collisions are all-inclusively formulated and discussed. Production cross sections of the radiations are calculated in terms of the second Born approximation. The cross sections of atomic bremsstrahlung production and radiative ionization have been estimated and compared with experimental results of continuum x rays from an A1 target bombarded with few-MeV protons. It is found that atomic bremsstrahlung is the most predominant component in the region of x-ray energy $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\ge}{T}_{m}$, where ${T}_{m}$ is the maximum energy transferred from a projectile to a free electron at rest, and the disagreement between the theory and experiment, which had previously been seen in this energy region, was clearly resolved.

The bremsstrahlung component of the diffuse galactic gamma-ray emission at MeV energies

view Abstract Citations (32) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The bremsstrahlung component of the diffuse galactic gamma-ray emission at MeV energies Sacher, W. ; Schoenfelder, V. Abstract Under the assumption that most of the observed gamma-ray flux below 30 MeV is produced by electron bremsstrahlung, restrictions on the energy spectrum of cosmic-ray electrons in interstellar space below 100 MeV are derived. The most accurate bremsstrahlung production cross sections of Koch and Motz and of Blumenthal and Gould are used in order to derive the bremsstrahlung production spectrum in interstellar space down to 10 keV-photon energies. If the low-energy gamma-ray emission, as seen by most observers, is indeed produced by electron bremsstrahlung, then a high interstellar electron flux at MeV energy results, which - at higher energies connects to the upper limit derived by Cummings, Stone, and Vogt. Such a high low-energy electron flux would be able to explain the ionization rate of 1 x 10 to the -15th ion pairs/(H-atoms) in H I regions. Publication: The Astrophysical Journal Pub Date: April 1984 DOI: 10.1086/161952 Bibcode: 1984ApJ...279..817S Keywords: Bremsstrahlung; Electron Flux Density; Galactic Cosmic Rays; Gamma Ray Astronomy; Interstellar Matter; Diffuse Radiation; Energy Spectra; Gamma Ray Spectra; H I Regions; Space Radiation full text sources ADS |

Gas dynamics in the impulsive phase of solar flares. I Thick-target heating by nonthermal electrons

A numerical investigation is carried out of the gas dynamical response of the solar atmosphere to a flare energy input in the form of precipitating nonthermal electrons. Rather than discussing the origin of these electrons, the spectral and temporal characteristics of the injected flux are inferred through a thick-target model of hard X-ray bremsstrahlung production. It is assumed that the electrons spiral about preexisting magnetic field lines, making it possible for a one-dimensional spatial treatment to be performed. It is also assumed that all electron energy losses are due to Coulomb collisions with ambient particles; that is, return-current ohmic effects and collective plasma processes are neglected. The results are contrasted with earlier work on conductive heating of the flare atmosphere. A local temperature peak is seen at a height of approximately 1500 km above the photosphere. This derives from a spatial maximum in the energy deposition rate from an electron beam. It is noted that such a feature is not present in conductively heated models. The associated localized region of high pressure drives material both upward and downward.

X‐ray production in thin films by electrons with energies between 40 and 100 keV. 1—Bremsstrahlung cross‐sections

AbstractCross‐sections for bremsstrahlung production in thin films may be derived theoretically only if certain approximations are made or if there is recourse to numerical techniques. In this paper, two approximate equations, one based on the Sommerfeld theory and the other on the Bethe–Heitler theory, are assessed for their accuracy in predicting cross‐sections differential in photon energy and emergence angle when a thin foil target is bombarded with electrons with energies between 40 and 100 keV. Experimental data are presented from eight different target materials and these are processed initially to make comparisons between experimental and theoretical spectral shapes and subsequently to compare observed and predicted absolute cross‐section values. Except for the heaviest target material (Au), the Bethe–Heitler theory provided a satisfactory description of all experimental observations. In contrast, the Sommerfeld theory provided a significantly inferior description of spectral shapes and consistently overestimated absolute cross‐sections by 15–20%.

Thick-target bremsstrahlung interpretation of short time-scale solar hard X-ray features

Steady-state analyses of bremsstrahlung hard X-ray production in solar flares are appropriate only if the lifetime of the high energy electrons in the X-ray source is much shorter than the duration of the observed X-ray burst. For a thick-target nonthermal model, this implies that a full time-dependent analysis is required when the duration of the burst is comparable to the collisional lifetime of the injected electrons, in turn set by the lengths and densities of the flaring region. In this paper we present the results of such a time-dependent analysis, and we point out that the intrinsic temporal signature of the thick-target production mechanism, caused by the finite travel time of the electrons through the target, may indeed rule out such a mechanism for extremely short duration hard X-ray events.

Bremsstrahlung production by potassium-40 in muscle

The bremsstrahlung spectrum produced when 1320 keV beta particles, emitted by the naturally occurring isotope 40K, are absorbed in muscle has been calculated. With reference to the external measurement of 239Pu in the lung using the 17 keV UL X-rays, a simple model was used to estimate the number of bremsstrahlung photons with energies between 12 and 25 keV that would emerge from the chest wall of a normal subject. This was calculated to be 3 min-1 for a detection area of 628 cm2, although internal bremsstrahlung may increase this to 4 in-1. The latter figure is a factor of approximately three lower than the counting rate observed when a pair of phoswich NaI detectors of the same total area are placed over an average subject. Possible reasons for this discrepancy are discussed.

Effects of a Nuclear Scattering Resonance on Bremsstrahlung Production and K-Shell Ionization

While the effects of nuclear resonances on nuclear bremsstrahlung emission have been the focus of current bremsstrahlung studies in nuclear physics, such effects on atomic K-shell ionization have attracted much attention recently. In this paper, we review the recent developments of these two topics with the emphasis upon their common features. Special attention is given to the effect of the nuclear resonance near 461 keV in p+12C where experimental results are available for bremsstrahlung production and K-shell ionization.

A study of charged particles associated with high- pT photons and pions

We report on the distributions of charge particles produced in association with high- p T prompt photons and neutral pions in pp collisions at s = 63 GeV and σ = 90° in the centre of mass. We find photons to be relatively unaccompanied by other particles at small angles with respect to the photon, and extract a measurement of the fraction of prompt photons due to bremsstrahlung production. The relative density of positive and negative particles in the system recoiling from the photon has been measured and compared with QCD motivated calculations.

Search for gluinos

Simply supersymmetric gauge theories predict the existence of gluinos, massive and long-lived colour octet spin 1/2 partners of the vector gluons. We discuss their phenomenology in e +e − annihilation - focusing on quarkonium decays as well as continuum production - and in deep inelastic scattering experiments - focusing on the energy-momentum sum rule and bremsstrahlung production at high Q 2. The best lower limit on the gluino mass comes from quarkonium decays and is about 3 GeV.

Multilepton study for search for new flavors and the Higgs boson

Multilepton events in high-energy hadron collisions are studied as a means to probe new particles in heavy-flavor associative production and ${Z}^{0}{H}^{0}$ bremsstrahlung production. We concentrate attention on trileptons. Some newly proposed transverse-momentum variables $T$, ${T}_{\ensuremath{\perp}}$, ${H}_{\ensuremath{\perp}}$ and the dilepton invariant mass $M(\mathrm{ll})$ provide useful signatures for the search for new particles.

The production of roentgenbremsstrahlung by transversely polarized electrons

The production of bremsstrahlung by transversely polarized electrons shows an azimuthal asymmetry. Measurements and calculations of this effect are presented. They indicate that the partial waves method — in the form used by Tseng and Pratt — is suitable to describe this polarization correlation.

Photon circular polarization as a neutral current effect in bremsstrahlung and pair production

Neutral-current induced photon circular polarization effects in bremsstrahlung and pair production are calculated to the first order in the weak interaction. The effects are found to be of the same order of magnitude as corresponding lepton-helicity effects. Numerical results are presented for the Weinberg-Salam model. A brief discussion of the pure electromagnetic photon circular polarization effects is given.

Isotope production with bremsstrahlung beams in comparison with proton beams

Electron accelerators can be used for the production of radioisotopes via bremsstrahlung beams generated in a suitable converter, mainly of high Z material. The amount of radioisotopes produced by ( γ, n) reactions in the giant resonance region and by (γ, spallation) reactions in the photomeson region are a factor of 10–100 smaller than the amounts produced by ( p, pn) nd ( p, spall.) reactions. The results of increasing the converter thickness, the angle θ and the target thickness on the bremsstrahlung production yields are discussed.

The production of neutral vector mesons by bremsstrahlung in electron-positron colliding beams

We study the bremsstrahlung production of the ϱ meson in the reaction e +e − → e +e − ϱ (→ e +e − π + π −). This reaction gives a C = −1 background which complicates the study of C = +1 two-photon processes at the new colliding-beam facilities. The cross section for the reaction rises from approximately 0.3 nb to 0.7 nb as the beam energy increases from 2 GeV to 15 GeV. From a study of the distributions of the final leptons and pions, we find a suitable choice of cuts which will reduce the event rate down to a small fraction of R. It is not possible to attribute the three-prong events seen at DELCO and PLUTO to this particular production mechanism.

Results on nucleon structure functions in quantum chromodynamics

Gluon bremsstrahlung processes inside the nucleon are investigated using the standard renormalization-group analysis. A new method of inverting the moments is applied which leads to analytic results for the parton distributions near $x=1$ and $x=0$. The nucleon is considered as a bound state of three quarks subsequently renormalized by gluon bremsstrahlung and quark-antiquark pair production. An unrenormalized valence quark distribution peaked at $x=\frac{1}{3}$, with a width related to the nucleon radius, leads to good agreement with deep-inelastic data. However, the gluon distribution obtained seems too steep near $x=0$.

Three-dimensional cascade showers in lead taking account of the Landau-Pomeranchuk-Migdal effect

Cascade showers in the ultrahigh-energy region are investigated, by taking into account the Landau-Pomeranchuk-Migdal effect in the processes of bremsstrahlung and pair production by the use of the full Monte Carlo method. Calculations are carried out in both one dimension and three dimensions and mean values, such as numbers of shower particles, mean square angular and lateral spread of particles and lateral structure functions, are obtained. These quantities are compared with results from cascade theory under approximationA and their features are discussed. The validity of the Monte Carlo method adopted is checked in individual processes in a cascade shower and is examined as a whole by comparing results from the simulation with those from the corresponding analytical theory.

Experimental calibration of a collimated NaI detector using large diameter sources

Calibration response functions have been obtained for a collimated 7.6 cm × 7.6 cm cylindrical sodium iodide detector at 13 different gamma energies. The sources have been prepared as highly active 10 cm squares which were rotated to simulate as a 0.76 m diameter disc emitting gamma photons isotropically with uniform emission over the disc surface area. The response functions include the effect of bremsstrahlung production and multiple Compton scattering in the lead of the collimator and show a response above the photopeak. For any experimental arrangement it is necessary to calibrate the detector over the full energy range using the same source-detector geometry and environment.

Internal Bremsstrahlung Production by Secondary Electrons Ejected by Proton Impact

Cross sections for bremsstrahlung production by ejected electrons in the electromagnetic field of incident proton is calculated using the theories of binary encounter approximation and of plane wave born approximation. It is shown that this bremsstrahlung becomes important in the region where the X-ray energy is higher than the maximum energy transfer Tm from the projectile to a free electron.

Bremsstrahlung Isochromats and Density of States: Chromium

We report the bremsstrahlung isochromat spectrum at a quantum energy of 5414 eV from a clean chromium surface prepared in an ultra-high-vacuum environment. This spectrum does not merely reflect the density of vacant states in chromium, nor is it the same as spectra recorded at 1240 eV by other workers: the assumption of final state symmetry independence of the transition probability for bremsstrahlung production is not justified. In order to quantitatively compare these spectra with band structure results consideration must be given to the effects of inelastic electron scattering as well as to the wave-vector and energy dependence of the transition probability.