THE EGS5 CODE SYSTEM

scattering is included (as an option) in EGS5.
Doppler broadening and linearly-polarized photon scattering
In addition to neglecting the binding of the electrons in the Compton interaction, standard EGS4
also ignored the motion of the electrons in the atomic cloud. Since this motion constitutes a distribution
of momenta, bound electrons ejected in Compton interactions emerge not, as assumed in
EGS4, with a single energy dependent on the scattering angle, but with a distribution of possible
energies. (This effect is usually called Doppler broadening.) Doppler broadening of Compton electron
energy spectra has been taken into account in EGS4 by Namito et al.[117], who demonstrated
improved calculations of the measured energy spectra for photon scattering at 40 keV. Explicit
modeling of this effect (on a shell-by-shell basis) is available (as an option) in standard EGS5.
Standard EGS4 also considered all particles to be unpolarized, using cross sections that have
been summed over incident and out-going particle polarizations. Namito et al.[116] introduced
polarized Compton and Rayleigh scattering in EGS4 and made comparisons with low-energy experiments
where gamma ray build-up factors and attenuation coefficients in water, iron and lead
were studied in the energy range 40–250 keV[74]. The effects of binding, Doppler broadening and
polarization are pronounced in the lower energy range studied 7 . Both effects can be modeled as
options in EGS5.
Electron impact ionization
Following the work of Namito and Hirayama[120, 122] K-shell electron-impact ionization (EII) is
included in EGS5. Six different representations of the cross sections for EII are supplied:
1. Casnati[43, 44]
2. Kolbenstvedt (original)[92]
3. Kolbenstvedt (revised)[105]
4. Jakoby[80]
5. Gryziński[66, 67, 65]
6. Gryziński (relativistic)[66, 67, 65]
7 Recent paper by Flöttmann[59] and others[93, 98] introduced polarization into EGS4, by means of the additionalcalls-to-AUSGAB
feature, in order to investigate the development of high-intensity positron sources for future linear
colliders.
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