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Bremsstrahlung, the emission of a photon by an electron scattering
from an atom, is a fundamental test process in which to study the
interaction of a photon and an electron in the field of an atom.
While the final state in this process includes both the scattered
electron and the emitted photon, and is described by a triply
differential cross section
,
the bulk of experimental
and theoretical efforts in studying electron-atom bremsstrahlung has
excluded observation of the outgoing electron. As such, the results
of these efforts are a doubly differential cross section
,
averaged over observable parameters of the outgoing electron (spin and
momentum). However, there has been some experimental and theoretical
work which includes observation of the scattered electron in
coincidence with the emitted photon. It is often argued that such
more complete experiments provide a more stringent test of the
theoretical models [1]. Here we present a comparison
of predictions from our new calculations, which use a full
relativistic partial wave and multipole decomposition, retaining all
important multipoles and partial waves, and the simpler approximations
of Bethe and Heitler [2] (lowest order Born
approximation) and Elwert and Haug [3] (using
Sommerfeld-Maue wave functions). We indeed find far larger
differences from the simpler theories for
than for
.
In a previous paper [4] we presented first results
from our triply differential electron-atom cross section (and
polarization correlation) code, comparing with available experimental
data (all for coplanar geometries). We also compared the predictions
of the simpler theories for these cases. The current work extends the
numerical comparison of the theories to a larger range of parameters,
including situations where no experimental data is presently
available. We examine both coplanar and non-coplanar geometries over
a broad range of scattering angles and electron and photon energies.
As with the previous work, we focus our discussion on heavy
elements (atomic number ), where the validity of both of the
simpler theories is in doubt. (Verification of our code was achieved,
in part, through comparisons with the simpler theories for lighter
elements [4]).

In Section 2 we discuss these various theories of
bremsstrahlung. In Section 3 we present results from
our numerical comparisons and, in Section 4, we
summarize our conclusions and suggest future experimental and theoretical
work.

** Next:** 2. Discussion of theories
** Up:** Comparison of relativistic partial
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*Eoin Carney*

*1999-06-14*