Last version:
FLUKA 2021.2.2, September 25th 2021
(last respin )
flair-2.3-0b 30-Jul-2021


-- Fluka Release
( 25.09.2021 )

FLUKA 2021.2.2 has been released.
Fluka Release 30.07.2021 FLUKA 2021.2.1 has been released.
Fluka Major Release 18.05.2021 FLUKA 2021.2.0 has been released.
Congratulations from INFN: ,
Dear Paola,
I wish to congratulate you and all the authors and collaborators for this new Fluka release, which looks at the future and confirms the support of INFN in the development and continuous improvement of this code.
best regards
Diego Bettoni
INFN Executive Committee

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Sets the size of the step of muons and charged hadrons to a fixed fraction of the kinetic energy in different materials


     WHAT(1) = fraction of the kinetic energy to be lost in a step
               (cannot be > 0.2)
               Default: if option DEFAULTS is used with SDUM = ICARUS, the
                        default is 0.02.
                        With SDUM = HADROTHErapy or PRECISIOn, the default
                        is 0.05.
                        If SDUM = CALORIMEtry, the default is 0.08.
                        With any other SDUM value, or if DEFAULTS is missing,
                        the default is 0.1.

     WHAT(2) = "epsilon" parameter used to check the finite size of the
               nucleus when the nuclear form factor is not invoked by
               the multiple scattering algorithm (see Note 3 below)
               For code development only, do not change!
               Default = 0.15

     WHAT(3) = high-energy limit for the fraction of energy to be lost
               in a step (the fraction is given by WHAT(3) times WHAT(1))
               For code development only, do not change!
               Default = 0.012

     WHAT(4) = lower index bound (or corresponding name) of materials where
               the specified energy loss per step is to be applied
               (From material WHAT(4)...)
               Default = 3

     WHAT(5) = upper index bound (or corresponding name) of materials where
               the specified energy loss per step is to be applied
               (... to material WHAT(5)...)
               Default = WHAT(4)

     WHAT(6) = step length in assigning indices
               ( steps of WHAT(6))
               Default = 1

     SDUM :   not used

     Default (option FLUKAFIX not given): the defaults listed above apply


  • 1) Usually there is no need for changing the default value of 10% (0.1) for WHAT(1)

  • 2) The input value is actually applied as such only at intermediate energies (between about a few tens of MeV and 1 GeV): at low energies it is slowly increased to twice the requested value, while at high energies it decreases to a limit controlled by WHAT(3), usually about one hundredth of the input value.

  • 3) The "epsilon" parameter controls the accuracy of the multiple scattering algorithm by limiting the step. In most cases the length of the step is practically limited anyway by the hadron interaction length, so the "epsilon" default value is of little importance and does not need to be changed. However, in some problems of large dimensions, especially when transporting muons, a small value of epsilon can slow down the calculations without necessity. In such cases, WHAT(2) can be safely set = 1000.0

Example (number based):

 FLUKAFIX        0.03        0.        0.       21.        0.        0.
 *  The maximum fractional energy loss for hadrons and muons is set to
 *  3 percent in material 21.

The same example, name-based:

 FLUKAFIX        0.03        0.        0.   CALCIUM        0.        0.

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