243 research outputs found
Epidemiological studies on radiation carcinogenesis in human populations following acute exposure: nuclear explosions and medical radiation.
The present review provides an understanding of our current knowledge of the carcinogenic effect of low-dose radiation in man, and surveys the epidemiological studies of human populations exposed to nuclear explosions and medical radiation. Discussion centers on the contributions of quantitative epidemiology to present knowledge, the reliability of the dose-incidence data, and those relevant epidemiological studies that provide the most useful information for risk estimation of cancer induction in man. Reference is made to dose-incidence relationships from laboratory animal experiments where they may obtain, for problems and difficulties in extrapolation from data obtained at high doses to low doses, and from animal data to the human situation. The paper describes the methods of application of such epidemiological data for estimation of excess risk of radiation-induced cancer in exposed human populations and discusses the strengths and limitations of epidemiology in guiding radiation protection philosophy and public health policy
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Geovisualization of dynamics, movement and change: key issues and developing approaches in visualization research
Production of carbon clusters to with a cryogenic buffer-gas beam source
Cryogenic buffer-gas beam sources are capable of producing intense beams of a
wide variety of molecules, and have a number of advantages over traditional
supersonic expansion sources. In this work, we report on a neon matrix
isolation study of carbon clusters produced with a cryogenic buffer-gas beam
source. Carbon clusters created by laser ablation of graphite are trapped in a
neon matrix and detected with a Fourier transform infrared spectrometer in the
spectral range . Through a study of carbon cluster
production as a function of various system parameters, we characterize the
behavior of the buffer-gas beam source and find that approximately
of each cluster is produced with each pulse of the ablation
laser. These measurements demonstrate the usefulness of cryogenic buffer-gas
beam sources for producing molecular beams of clusters.Comment: 7 pages, 4 figure
Dissociative electron attachment to halogen molecules: Angular distributions and nonlocal effects
Modifying the photodetachment near a metal surface by a weak electric field
We show the photodetachment cross sections of H near a metal surface can be
modified using a weak static electric field. The modification is possible
because the oscillatory part of the cross section near a metal surface is
directly connected with the transit-time and the action of the
detached-electron closed-orbit which can be changed systematically by varying
the static electric field strength. Photodetachment cross sections for various
photon energies and electric field values are calculated and displayed.Comment: 16 pages, 7 figure
Propagation of charged particle waves in a uniform magnetic field
This paper considers the probability density and current distributions
generated by a point-like, isotropic source of monoenergetic charges embedded
into a uniform magnetic field environment. Electron sources of this kind have
been realized in recent photodetachment microscopy experiments. Unlike the
total photocurrent cross section, which is largely understood, the spatial
profiles of charge and current emitted by the source display an unexpected
hierarchy of complex patterns, even though the distributions, apart from
scaling, depend only on a single physical parameter. We examine the electron
dynamics both by solving the quantum problem, i. e., finding the energy Green
function, and from a semiclassical perspective based on the simple cyclotron
orbits followed by the electron. Simulations suggest that the semiclassical
method, which involves here interference between an infinite set of paths,
faithfully reproduces the features observed in the quantum solution, even in
extreme circumstances, and lends itself to an interpretation of some (though
not all) of the rich structure exhibited in this simple problem.Comment: 39 pages, 16 figure
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