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Photon Spectrum From Bremsstrahlung

Description: Abstract: The number of photons of given energy radiated in Bremsstrahlung collision of electrons with nuclei is calculated relativistically. Expansions are obtained for energies small to mc-squared. The photon spectrum is averaged over a Maxwell distribution for the electrons. Numerical results are included.
Date: August 11, 1953
Creator: Gluckstern, R. L.; Hull, M. H., Jr. & Breit, G.
Partner: UNT Libraries Government Documents Department

Energetic Proton Generation in Ultra-Intense Laser-Solid Interactions

Description: An explanation for the energetic ions observed in the PetaWatt experiments is presented. In solid target experiments with focused intensities exceeding 10{sup 20} W/cm{sup 2}, high-energy electron generation, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. In this report, we attempt to explain the physical process present that will explain the presence of these energetic protons, as well as explain the number, energy, and angular spread of the protons observed in experiment. In particular, we hypothesize that hot electrons produced on the front of the target are sent through to the back off the target, where they ionize the hydrogen layer there. These ions are then accelerated by the hot electron cloud, to tens of MeV energies in distances of order tens of microns, whereupon they end up being detected in the radiographic and spectrographic detectors.
Date: March 1, 2000
Creator: Wilks, S.C.; Langdon, A.B.; Cowan, T.E.; Roth, M.; Singh, M.; Hatchett, S. et al.
Partner: UNT Libraries Government Documents Department

Photon dosimetry using plastic scintillators in pulsed radiation fields

Description: Simulations and experiments have been carried out to explore using a plastic scintillator as a dosimetry probe in the vicinity of a pulsed bremsstrahlung source in the range 4 to 20 MeV. Taking advantage of the tissue-equivalent properties of this detector in conjunction with the use of a fast digital signal processor near real-time dosimetry was shown to be possible. The importance of accounting for a broad energy electron beam in bremsstrahlung production, and photon scattering and build-up, in correctly interpreting dosimetry results at long stand-off distances is highlighted by comparing real world experiments with ideal geometry simulations. Close agreement was found between absorbed energy calculations based upon spectroscopic techniques and calculations based upon signal integration, showing a ratio between 10 MeV absorbed dose to 12 MeV absorbed dose of 0.66 at a distance of 91.4 m from the accelerator. This is compared with an idealized model simulation with a monoenergetic electron beam and without scattering, where the ratio was 0.46.
Date: April 1, 2007
Creator: Chichester, David L.; Blackburn, Brandon W.; Johnson, James T. & Watson, Scott W.
Partner: UNT Libraries Government Documents Department

Quantum Suppression of beamstrahlung for future linearcolliders

Description: Beamstrahhmg at interaction point may present severe lim- itations on linear collider performance. The approach to re- duce this effect adopted for all current designs at 0.5 TeV will become more difficult and less effective at higher en- ergy. We discuss the feasibility of an alternative approach, based on an effect known as quantum suppression of beam- strahlung, for future linear colliders at multi-TeV energy.
Date: June 1, 1998
Creator: Xie, Ming
Partner: UNT Libraries Government Documents Department

Polarization of Bremsstrahlung

Description: Abstract: Numerical information necessary to an experimental study of the polarization of bremsstrahlung is presented. One may conclude that it is possible to produce significantly polarized γ-ray beams with existing electron accelerators. These beams will provide a new tool for the study of photonuclear reactions over a wide range of energy.
Date: September 3, 1954
Creator: Karplus, Robert & Reifman, Alfred
Partner: UNT Libraries Government Documents Department

Note on Inverse Bremsstrahlung in a Strong Electromagnetic Field.

Description: The collisional energy loss of an electron undergoing forced oscillation in an electromagnetic field behaves quite differently in the low and high intensity limits. In the case where the thermal velocity v{sub t} is much larger than v{sub 0} = eE{sub 0}m{omega} the rate at which the electron transfers energy to the random motion of the medium is proportional to v{sub 0}{sup 2}. It is shown that in the case of an electromagnetic field v{sub 0} >> v{sub t} the rate of transfer is much slower, and actually decreases with the strength of the field.
Date: January 1, 1972
Creator: Bethe, H. A.
Partner: UNT Libraries Government Documents Department

Inverse bremsstrahlung absorption coefficient and initiation of laser- supported detonation waves in air

Description: The inverse bremsstrahlung absorption coefficient in LASNEX was modified for application to laser effects calculations at temperatures below 10 eV. These modifications are described and the initiation condition for a laser-supported detonation (LSD) wave is crudely estimated for air in the vicinity of a solid target. (auth)
Date: December 1, 1973
Creator: Winslow, A. M.
Partner: UNT Libraries Government Documents Department

Femtosecond electron and x-ray generation by laser andplasma-based sources

Description: The generation of ultra-short x-rays by Thomson scattering intense laser pulses from electron beams is discussed, including recent experimental results and methods for enhancing the x-ray flux. A high flux of x-rays in a femtosecond pulse requires the generation of femtosecond electron bunches and a head-on Thomson scattering geometry. The generation of ultrashort electron bunches in a plasma-based accelerator with an injection technique that uses two colliding laser pulses is discussed. Simulations indicate the bunches as short as a few fs can be produced. Conversion of the fs electron pulse to a fs x-ray pulse can be accomplished by Bremsstrahlung or Thomson scattering.
Date: February 1, 2000
Creator: Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Applications of Photonuclear Physics for International Safeguards and Security

Description: Studies of nuclear resonance fluorescence based applications are presented. Important for these applications are data for isotopes such as {sup 239}Pu. Nuclear resonance fluorescence measurements of {sup 239}Pu were performed at the free electron laser facility at UC Santa Barbara using photons from a bremsstrahlung beam with an endpoint energies between 4.0 MeV and 5.5 MeV. Though no discrete states with significant confidence level were measured, we have excluded the region above 27(3) eV-barns, or 4-sigma, where we would expect only a small chance of false positives. Details of the measurements and the results are presented here.
Date: April 16, 2010
Creator: Johnson, M S; Hall, J M; McNabb, D P; McFarland, J; Norman, E; Bertozzi, W et al.
Partner: UNT Libraries Government Documents Department

Time-resolved Temperature Measurements in SSPX

Description: We seek to measure time-resolved electron temperatures in the SSPX plasma using soft X-rays from free-free Bremsstrahlung radiation. To increase sensitivity to changes in temperature over the range 100-300 eV, we use two photodiode detectors sensitive to different soft X-ray energies. The detectors, one with a Zr/C coating and the other with a Ti/Pd coating, view the plasma along a common line of sight tangential to the magnetic axis of the spheromak, where the electron temperature is a maximum. The comparison of the signals, over a similar volume of plasma, should be a stronger function of temperature than a single detector in the range of Te< 300 eV. The success of using photodiodes to detect changing temperatures along a chord will make the case for designing an array of the detectors, which could provide a time changing temperature profile over a larger portion of the plasma.
Date: August 14, 2006
Creator: Ludington, A R; Hill, D N; McLean, H S; Moller, J & Wood, R D
Partner: UNT Libraries Government Documents Department

STATUS OF THE DARHT PASE 2 LONG-PULSE ACCELERATOR

Description: The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron Linear Induction Accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography. We intend to produce measurements containing three-dimensional information with sub-millimeter spatial resolution of the interior features of very dense, explosively-driven objects. The facility will be completed in two phases with the first phase having become operational in July 1999 utilizing a single-pulse, 20-MeV, 2-kA, 60-ns accelerator, a high-resolution electro-optical x-ray imaging system, and other hydrodynamics testing systems. The second phase will be operational in 2004 and features the addition of a 20-MeV, 2-kA, 2-microsecond accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved x-ray images. The second phase also features an extended, high-resolution electro-optical x-ray system with a framing speed of 1.6-MHz. Production of the first beam from the Phase 2 injector will occur this year. In this paper we will present the overall design of the Phase 2 long-pulse injector and accelerator as well as some component test results. We will also discuss the downstream transport section that contains the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography as well as the x-ray conversion target assembly. Selected experimental results from this area of the project will also be included. Finally, we will discuss our plans for initial operations.
Date: January 1, 2001
Creator: Burns, M. J. (Michael J.); Carlsten, B. E. (Bruce E.); Davis, H. A. (Harold A.); Ekdahl, C. A. (Carl A.); Fortgang, C. M. (Clifford M.); McCuistian, B. T. (Brian T.) et al.
Partner: UNT Libraries Government Documents Department

Electron and Photon Interactions in the Regime of Strong LPM Suppression

Description: Most searches for ultra-high energy (UHE) astrophysical neutrinos look for radio emission from the electromagnetic and hadronic showers produced in their interactions. The radio frequency spectrum and angular distribution depend on the shower development, so are sensitive to the interaction cross sections. At energies above about 1016 eV (in ice), the Landau-Pomeranchuk-Migdal (LPM) effect significantly reduces the cross sections for the two dominant electromagnetic interactions: bremsstrahlung and pair production. At higher energies, above about 1020 eV, the photonuclear cross section becomes larger than that for pair production, and direct pair production and electronuclear interactions become dominant over bremsstrahlung. The electron interaction length reaches a maximum around 1021 eV, and then decreases slowly as the electron energy increases further. In this regime, the growth in the photon cross section and electron energy loss moderates the rise in nu e shower length, which rises from ~;;5 m at 1016 eV to ~;;40 m at 1019 eV and ~;;100 m at 1020 eV, but only to ~;;300 m at 1024 eV. In contrast, without photonuclear and electronuclear interactions, the shower length would be over 10 km at 1024 eV.
Date: June 10, 2010
Creator: Gerhardt, L. & Klein, S.
Partner: UNT Libraries Government Documents Department

FREE-FREE GAUNT FACTORS

Description: The hydrogenic (unscreened coulomb) free-free gaunt factors are computed for a wide range of initial energies and photon frequencies. In addition, an average over initial energies with the Maxwell-Boltzmann distribution is performed to give the temperatureaveraged gaunt factors for use in opacity calculations. These are presented as functions of Z/sup 2//kT and h nu /kT. The relation between these gaunt factors and the rate of bremsstrahlung energy production is given, as is the total energy emitted as a function of Z/sup 2//kT. (auth)
Date: November 1, 1957
Creator: Karzas, W.J. & Latter, R.
Partner: UNT Libraries Government Documents Department

XUV Absorption by Solid Density Aluminum

Description: An inverse bremsstrahlung model for plasmas and simple metals that approximates the cold, solid Al experimental data below the L-edge is applied to matter conditions relevant to XUV laser applications. The model involves an all-order calculation using a semi-analytical effective electron-ion interaction. The predicted increases in XUV absorption with rising temperature occur via two effects: increased availability of final states from reduced electron degeneracy and a stronger electron-ion interaction from reduced screening. Discrepancies in the temperature dependence as well as other details between the present approach and a recently proposed absorption model are discussed.
Date: September 21, 2009
Creator: Iglesias, C A
Partner: UNT Libraries Government Documents Department

Bremstrahlung versus Monoenergetic Photons for Photonuclear Inspection Applications

Description: Bremsstrahlung sources have been utilized for various non-intrusive inspection or interrogation applications for over 100 years - with the primary focus being radiographic imaging. In the last several decades, it has become evident that photons of energy greater than 6 MeV can also provide useful photonuclear information that can extend the capabilities and information available from active inspections. These energetic inspection photons can be produced as a continuum of energies (i.e., bremsstrahlung distribution) or as a set of one or more discrete photon energies (i.e., monoenergetic distribution). This paper will discuss the photonuclear process and its energetic photon energy dependence, will discuss the photonuclear role in nuclear material detection, will present applicable photon sources along with their field deployment status, and highlight some advantages and disadvantages of bremsstrahlung and monoenergetic photons sources.
Date: June 1, 2008
Creator: Jones, Dr. James L.
Partner: UNT Libraries Government Documents Department

Status of the Dual-Axis Radiographic Hydrodynamics Test Facility

Description: The Dual-Axis Radiographic Hydrodynamics Test (DARHT) Facility will employ two electron linear induction accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography with sub-millimeter spatial resolution of very dense (attentuations>10{sup 5}), dynamic objects. We will produce an intense x-ray pulse using a 19.75-MeV, 3.5-4 kA, 60-ns flattop electron beam focused on a tungsten target. A 3.75-MeV injector with either a cold velvet cathode or a laser-driven photocathode will produce a beam to be accelerated through a series of 64 ferrite-loaded induction cells with solenoid focusing. Accelerator technology demonstrations have been underway for several years at the DARHT Integrated Test Stand and results including beam energy, emittance, and beam breakup measurements are discussed.
Date: September 1, 1996
Creator: Burns, M.J.; Allison, P.W.; Carlson, R.L.; Downing, J.N.; Moir, D.C. & Shurter, R.P.
Partner: UNT Libraries Government Documents Department

EM-PIC simulations of e-beam interaction with field emitted ions from bremsstrahlung targets

Description: We investigate electron beam defocusing caused by field emitted ions from the bremsstrahlung target of a radiography machine using fully electromagnetic particle-in-cell simulations. This possibly deleterious effect is relevant to both current radiography machines (FXR) and machines being built (DARHT-2) or planned (AHF). A simple theory of the acceleration of ions desorbed from the heated target, and subsequent beam defocusing due to partial charge neutralization is in reasonable agreement with the more detailed simulations. For parameters corresponding to FXR (I{sub b}=2.3 kA, {epsilon}{sub b}=16 MeV), simulations assuming space-charge-limited emission of protons predict prompt beam defocusing. Time integrated spot-size measurement, however, is dominated by early-time small spot brightness, and so is not a sensitive diagnostic. Comparisons are made to available FXR data. We also investigate use of a recessed target geometry to mitigate field emitted ion acceleration; only modest improvements are predicted.
Date: August 13, 1998
Creator: Rambo, P. W., LLNL
Partner: UNT Libraries Government Documents Department

Initial Results from an In-Vacuum Undulator in the NSLS X-ray Ring

Description: A short period, in vacuum undulator for the NSLS X-Ray Ring has been developed and has achieved its project design goals during commissioning studies. The device is called IVUN (In-Vacuum UNdulator) and employs magnet arrays (31 periods, with an 11 mm period) developed at SPring-8, while the requisite vacuum chamber and mechanical systems were developed at the NSLS. At a magnet gap of 3.3 mm, IVUN produces 4.6 keV radiation in the fundamental, with useful photon fluxes in both the 2nd and 3rd harmonics. The magnet gap is adjustable between 2 mm and 10 mm. A brief overview of IVUN is presented, together with initial commissioning results: the dependence of electron beam lifetime and bremsstrahlung on magnet gap, and the output radiation spectrum.
Date: November 1, 1997
Creator: Stefan, P.M.; Krinsky, S.; Rakowsky, G.; Solomon, L.; Tanabe, T. & Kitamura, H.
Partner: UNT Libraries Government Documents Department

Measurement of gas bremsstrahlung from the insertion device beamlines of the advanced photon source

Description: High energy electron storage rings generate energetic bremsstrahlung photons through radiative interaction of the electrons (or positrons) with the residual gas molecules inside the storage ring. The resulting radiation exits at an average emittance angle of (m{sub 0}c{sub 2}/E) radian with respect to the electron beam path, where m{sub 0}c{sup 2} is the rest mass of E the electron and E its kinetic energy. Thus, at straight sections of the storage rings, moving electrons will produce a narrow and intense monodirectional photon beam. At synchrotron radiation facilities, where beamlines are channeled out of the storage ring, a continuous gas bremsstrahlung spectrum, with a maximum energy of the electron beam, will be present. There are a number of compelling reasons that a measurement of the bremsstrahlung characteristics be conducted at the Advanced Photon Source (APS) storage ring. Although the number of residual gas molecules present in the storage ring at typical nTorr vacuum is low, because of the long straight paths of the electrons in the storage ring at APS, significant production of bremsstrahlung will be produced. This may pose a radiation hazard. It is then imperative that personnel be shielded from dose rates due to this radiation. There are not many measurements available for gas bremsstrahlung, especially for higher electron beam energies. The quantitative estimates of gas bremsstrahlung from storage rings as evaluated by Monte Carlo codes also have several uncertainties. They are in general calculated for air at atmospheric pressure, the results of which are then extrapolated to typical storage ring vacuum values (of the order of 10{sup -9} Torr). Realistically, the actual pressure profile can vary inside the narrow vacuum chamber. Also, the actual chemical composition of the residual gas inside the storage ring is generally different from that of air.
Date: March 1, 1997
Creator: Pisharody, M.; Job, P.K. & Magill, S.
Partner: UNT Libraries Government Documents Department