Last version:
FLUKA 2021.2.4, January 11th 2022
(last respin )
flair-2.3-0b 30-Jul-2021


-- Fluka Release
( 11.01.2022 )

FLUKA 2021.2.4 has been released.

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sets different energy transport cutoffs for hadrons, muons and neutrinos


The meaning of WHAT(1) depends also on the value of WHAT(5).

    For WHAT(5) = 0.0 :
     WHAT(1) < 0.0 : kinetic energy cutoff (GeV)
             > 0.0 : momentum cutoff (GeV/c)
    For WHAT(5) >= 1.0 :
     WHAT(1) < 0.0 : gamma cutoff (Lorentz factor, = E/mc**2)
             > 0.0 : eta cutoff (= beta*gamma = v/c E/mc**2)
             Default (WHAT(1) = 0.0): the cutoff is 0 for neutrinos,
               and 1.E-14 GeV for neutrons.
               For any other hadrons, and for muons:
               if option DEFAULTS is missing, or is present with
               SDUM = NEW-DEFAults or SHIELDINg, the default cutoff
               kinetic energy is 0.01 GeV.
               If SDUM = HADROTHErapy, ICARUS or PRECISIOn, the default
               cutoff kinetic energy is 0.0001 GeV.
               If SDUM = CALORIMEtry, the default cutoff kinetic energy
               is = 0.001 * m/m_p GeV (m = particle mass, m_p = proton mass)
               In any other case, the default cutoff is 0.050 GeV.
               (For e+e- and photons the threshold is set by EMFCUT, see
               Note 3 below).

     WHAT(2) = lower bound of the particle id-numbers to which the cutoff
               applies ("From particle WHAT(2)...").
               Default = 1.0

     WHAT(3) = upper bound of the particle id-numbers to which the cutoff
               applies (" particle WHAT(3)...").
               Default = WHAT(2)

     WHAT(4) = step length in assigning numbers
               (" steps of WHAT(4)")
               Default = 1.0.

     WHAT(5) : depending on its value, cutoff values indicated by
               WHAT(1) are assigned to kinetic energy, momentum, gamma or
               eta (see WHAT(1))

     WHAT(6) = 1.0 restricts the given cutoff to charged particles only
               Default: the cutoff applies to all particles indicated by

     SDUM :    not used

     Default (option PART-THR not given): thresholds as described above
            for WHAT(1) = 0.0.


  • 1) If low-energy neutron transport is not requested (explicitly via LOW-NEUT or implicitly via DEFAULTS), the energy of neutrons below threshold is deposited on the spot.

  • 2) The total momentum cutoffs of heavy ions are derived from that of a 4He ion (4-HELIUM) by scaling the latter with the ratios of the atomic weights of the heavy ions and the 4He ion. The total momentum cutoffs for light ions (4-HELIUM, 3-HELIUM, TRITON and DEUTERON) can be defined by PART-THRes. If this is not done, they are derived from that one of a proton by scaling the latter with the ratios of the atomic weights of the light ions and a proton.

  • 3) Option PART-THR acts on all particles excepted e+ e- and photons, while EMFCUT option is used to set to transport electrons, positrons and photons.

  • 4) When the energy of a heavy charged particle becomes lower than the cutoff defined by PART-THR, and if such cutoff is lower than 100 MeV, the particle is not stopped, but is ranged out to rest in an approximate way. Its kinetic energy is deposited uniformly over the residual range if the latter is contained within a single region; otherwise a new residual range is calculated at each boundary crossing and the residual kinetic energy is distributed accordingly. If applicable, such a particle eventually decays at rest or is captured. All other forms of transport are ignored excepted curved paths in magnetic fields (multiple scattering, delta ray production, inelastic or elastic collisions, and INCLUDING DECAY IN FLIGHT). Magnetic fields are taken into account but only very roughly, since the continuous slowing down of the particles is not simulated. Antiprotons and pi-minus are always ranged out to rest (without allowance for decay) and made to annihilate on a nucleus.

  • 5) If the cutoff is higher than 100 MeV, however, the particles are stopped in place without any further treatment. If this happens at a boundary crossing where the material of the region entered is vacuum, a printed message warns the user that energy is being deposited in vacuum.

  • 6) By default the neutron threshold is set at 1.E-14 GeV (1.E-5 eV, the lowest boundary of the group structure). So, normally it is not necessary to issue a PART-THR command at all for neutrons. A note of caution: if a PART-THR has been issued spanning all particles, it is generally necessary to override it with another one resetting the threshold for neutrons to 1.E-14 GeV. As a general rule however, if a neutron transport threshold is set < 20 MeV, it is rounded to the closest lower group boundary.


 * A threshold of 2 MeV (kinetic energy) is requested for heavy charged
 * particles with id-numbers between 1 and 11 (protons, antiprotons and
 * muons). A threshold of Gamma (E/m) = 2 will apply for pions and kaons
 * (numbers from 13 to 16). For all other particles, the defaults will apply.
 PART-THR      -0.002       1.0      11.0       0.0       0.0       1.0
 PART-THR        -2.0      13.0      16.0       1.0       1.0       0.0

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