THE EGS5 CODE SYSTEM

Transport Steps,
∆ E = E x ESTEPE
transport step 1 transport step 2
∆ E1= DEINITIAL1+ DERESID1
∆ E2 = DEINITIAL2 + DERESID2
DEINITIAL1 DERESID1 DEINITIAL2 DERESID2
energy hinge 1
ΚΕ = ΚΕ −
∆ Ε1
energy hinge 2
KE = KE − ∆ Ε2
initial translation step, translation step 2,
translation step 3,
DEINITIAL1 DERESID1 + DEINITIAL2 DERESID2 + DEINITIAL3
Translation Steps, between random hinge points
Figure 2.13: Translation steps and transport steps for energy loss hinges. The top half of the
figure illustrates the step size (in terms of energy loss) for consecutive conventional Monte Carlo
transport steps, with the energy loss set at a constant fraction of the current kinetic energy (E
times ESTEPE as in EGS4, for example). The lower schematic shows how these steps are broken
into a series of translation steps between randomly determined hinge distances. Transport through
the translation steps is mono-energetic, with full energy loss being applied at the hinge points.
Note that the second translation step, for which the electron kinetic energy is constant, actually
involves moving the electron through pieces of 2 different transport steps. Multiple scattering could
interrupt this energy step translation at any point or at several points, but does not impact the
energy transport mechanics.
steps thus overlap rather than correspond, as illustrated in Figure 2.13.
Variables which contain information about the full distance to the next hinge (the translation
step), the part of that distance which is the initial part of the current transport step, and the
residual (post-hinge) distance remaining to complete the current transport step, for both energy
loss and deflection, must now be stored while the particle is being transported. Again, it is not the
distances themselves but rather the energy losses and scattering strengths which matter, and in
EGS5, these variables are called DENSTEP, DEINITIAL and DERESID, for the energy loss hinge and
K1STEP, K1INIT and K1RSD, for the the multiple scattering hinge. For reasons discussed below,
only the scattering strength variables become part of the particle stack; the energy loss hinge
variables are all local to the current particle only.
Several interesting consequences arise from the use of energy hinge mechanics. Even though
the electron energy is changed only at the energy hinge point, energy deposition is modeled as
occurring along the entire electron transport step, and the EGS4 energy loss variable EDEP, which
has been retained in EGS5, is computed along every translation step, and passed to the user for
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