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Title: Bremsstrahlung Production

  1. Los Alamos National Laboratory
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Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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Resource Relation:
Conference: Radiography Working Group ; 2013-01-09 - 2013-01-09 ; Albuquerque, New Mexico, United States
Country of Publication:
United States
Mathematics & Computing(97)

Citation Formats

Wood, William Monford. Bremsstrahlung Production. United States: N. p., 2015. Web.
Wood, William Monford. Bremsstrahlung Production. United States.
Wood, William Monford. Mon . "Bremsstrahlung Production". United States. doi:.
title = {Bremsstrahlung Production},
author = {Wood, William Monford},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 23 00:00:00 EST 2015},
month = {Mon Feb 23 00:00:00 EST 2015}

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  • Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed.
  • We have developed an experimental apparatus to study radionuclide production by photonuclear reactions. A nearly neutron-free bremsstrahlung beam was created by incident electron interactions with a tantalum radiator. We studied photonuclear reactions in different samples, including the elements Be, Na, Si, Cl, and Ge. Decay gamma rays from radionuclides having half lives > 2 min were analysed. Using the PICA code, we calculated the yield of radionuclides for silicon. We have observed and assigned a new gamma ray transition, of E({gamma}) = 1153 keV, to the decay of 6.6 min 29-Al.
  • Measurements are presented of anomalously large microwave absorption near the electron plasma frequency $omega$/sub p/ by a completely ionized plasma. The threshold electric field required for the onset of anomalous absorption has been measured over a density range that is large enough to separate clearly the effects of Landau and collisional damping. Good agreement is demonstrated between these measurements and the threshold values predicted by a computer solution of the exact dispersion relation for AC parametric instabilities. Energy distribution measurements are presented for the hot, non-thermal electron tail produced by such anomalous absorption. The nature of these distributions depends stronglymore » upon ($omega$/sub p//$omega$)$sup 2$ and microwave power. In some cases a large fraction of the anomalously absorbed power goes into less than 1 percent of the electrons and a bump develops on the hot tail. Below the threshold for anomalous absorption, the classical electron-ion collision rate, v/ sub ei/, from a measurement of the inverse bremsstrahlung absorption rate has been deduced. The first experimental evidence that intense electromagnetic fields modify v/sub ei/ is reported. Observations from these experiments yield a simple empirical relation that applies for AC drift speeds as large as eE/ (m$omega$) approximately (kT/sub e//m)/sup 1/2/. Ohmic heating is minimized in these experiments by use of very short microwave pulses. (auth)« less