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7.10} Energy cutoffs

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 Setting energy cutoffs, for both transport and production, is an important
 responsibility of the user, who is interested in choosing the best compromise
 between accuracy and time efficiency. Each of the parameter sets available via
 option DEFAULTS, including the basic defaults set which exists when that option
 has not been explicitly requested, offers a well-optimised choice for the
 corresponding class of applications, with only one exception. But even so, it
 is often convenient to override some of the default cutoffs in order to
 improve performance. The exception concerns the default particle production
 cutoffs for electrons, positrons and photons, which are dependent on other
 settings (see EMFCUT below).

 Transport cutoffs, or thresholds, are set with command PART-THRes for hadrons
 and muons, with EMFCUT for electrons, positrons and photons, and with LOW-BIAS
 for low-energy neutrons.  Despite the similar functionality of the three
 commands, there are important differences in their syntax and in the way the
 threshold is implemented for the three families of particles. PART-THRes can
 assign different transport thresholds to different particles, but the
 thresholds are the same in all materials and regions.  When the hadron or muon
 energy becomes lower than the relevant threshold, the particle is not stopped
 but ranged out in a simplified way. Because the electron and photon cutoffs
 are more critical with respect to calculation accuracy, EMFCUT can assign
 transport thresholds on a region basis: on the other hand no ranging out is
 performed, due to the difficulty to clearly define electron ranges.  For
 low-energy neutrons, the transport threshold is set by LOW-BIAS also on a
 region basis, but as a group number rather than an energy.

 Two input commands can set particle production cutoffs, respectively for heavy
 particles and for electrons, positrons and photons.
 Thresholds for delta ray production by charged hadrons and muons are assigned,
 on a material basis, by means of option DELTARAY. Energy transfers to electrons
 lower than the threshold are handled in the continuous slowing down
 approximation. Production of bremsstrahlung by electrons and of Möller/Bhabha
 secondary electrons is simulated explicitly above thresholds set on a material
 basis with option EMFCUT. Defaults for electron and photon production cutoffs
 are dependent on other settings in a complex way. Therefore it is recommended
 to check the values printed on standard output, or to set EMFCUT production
 cutoffs explicitly for each material. Note also that the same EMFCUT command
 is used to set both transport and production cutoffs: but the setting is done
 by region in the first case and by material in the second.

 To complete the list of commands used for cutoff setting, we will mention
 THRESHOLd, which is used to set an energy threshold for star scoring. In
 principle, a "star" is any high energy inelastic hadron interaction
 (spallation) and star density has always been one the quantities which can be
 scored by FLUKA. Since a popular technique to estimate induced radioactivity
 was based originally on the density of stars produced by hadrons with energies
 higher than 50 MeV, the possibility to set a scoring energy limit is provided.


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