Adapting the parameters of the physical processes

For dosimetry problems a DEFAULT like PRECISIO is recommended. Let us remind that this choice implies the following: EMF on; Rayleigh scattering and inelastic form factor corrections to Compton scattering activated; detailed photoelectric edge treatment and fluorescence photons activated; low energy neutron transport on (high energy neutron threshold at 19.6 MeV), fully analogue absorption for low energy neutrons, particle transport threshold set at 100 keV, except neutrons, (19.6 MeV), antineutrons (50 MeV), and (anti)neutrinos (0, but discarded); multiple scattering threshold at minimum allowed energy both for primary and secondary charged particles; delta ray production on with threshold 100 keV; restricted Landau fluctuations on both for hadrons/muons and EM particles; tabulation ratio for hadron/muon dE/dx set at 1.04; fraction of the kinetic energy to be lost in a step set at 0.05; number of dp/dx tabulation points set at 80; heavy particle e+/e- pair production activated with full explicit production; heavy particle bremsstrahlung activated with explicit photon production above 300 keV; Muon photonuclear interactions activated with explicit generation of secondaries; heavy fragment transport activated. Of course it can be convenient to overwrite some of the choices. As an example, difficulties in considering the low operating pressure of the machine, mentioned in the previous section, cannot be solved completely by the trick to work at atmospheric pressure and to scale the final results. This because the multiple scattering is practically negligible in the vacuum chamber of a storage ring, while it is responsible of large broadening of the beam at atmospheric pressure. Therefore it must be suppressed in the FLUKA simulations and this is driven by means of the MULSOPT card.

In addition, the threshold for the Möller scattering of the electrons has been set at 10 MeV to minimize any angular deflection due to the production of $\delta$ rays (EMFCUT card). Notice the use of the EMFCUT card with ELPO-THR parameter, to give the kinetic energy threshold (GeV) for e$^+$e$^-$ bremsstrahlung. The code energy cuts are set at 50 keV for charged particles and 1 keV for photons (see again the EMFCUT cards). Here the user is also invited to notice the use of the EMFFIX directive to set the size of electron steps corresponding to a fixed fraction of the total energy. We remind here that by default the energy lost per step is 20% for all materials. This is acceptable for most routine problems. In dosimetry problems and in thin-slab geometries it is recommended not to exceed 5-10%. This option is used also in conjunction with the STEPSIZE directive, in order to set the allowed maximum step length (in cm) in different regions. For a detailed discussion of the step length problem see [2]