THE EGS5 CODE SYSTEM

Transport Steps,∆ E = E x ESTEPEtransport step 1 transport step 2∆ E1= DEINITIAL1+ DERESID1∆ E2 = DEINITIAL2 + DERESID2DEINITIAL1 DERESID1 DEINITIAL2 DERESID2energy hinge 1ΚΕ = ΚΕ −∆ Ε1energy hinge 2KE = KE − ∆ Ε2initial translation step, translation step 2,translation step 3,DEINITIAL1 DERESID1 + DEINITIAL2 DERESID2 + DEINITIAL3Translation Steps, between random hinge pointsFigure 2.13: Translation steps and transport steps for energy loss hinges. The top half of thefigure illustrates the step size (in terms of energy loss) for consecutive conventional Monte Carlotransport steps, with the energy loss set at a constant fraction of the current kinetic energy (Etimes ESTEPE as in EGS4, for example). The lower schematic shows how these steps are brokeninto a series of translation steps between randomly determined hinge distances. Transport throughthe 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, actuallyinvolves moving the electron through pieces of 2 different transport steps. Multiple scattering couldinterrupt this energy step translation at any point or at several points, but does not impact theenergy 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 translationstep), the part of that distance which is the initial part of the current transport step, and theresidual (post-hinge) distance remaining to complete the current transport step, for both energyloss and deflection, must now be stored while the particle is being transported. Again, it is not thedistances themselves but rather the energy losses and scattering strengths which matter, and inEGS5, these variables are called DENSTEP, DEINITIAL and DERESID, for the energy loss hinge andK1STEP, 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 hingevariables are all local to the current particle only.Several interesting consequences arise from the use of energy hinge mechanics. Even thoughthe electron energy is changed only at the energy hinge point, energy deposition is modeled asoccurring along the entire electron transport step, and the EGS4 energy loss variable EDEP, whichhas been retained in EGS5, is computed along every translation step, and passed to the user for105