FLUKA: MULSOPT
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MULSOPT
Sets the tracking conditions for multiple Coulomb scattering (MCS), for both
hadrons/muons and e+/e- particles. Can also be used to activate single scattering.
See also EMFFIX, FLUKAFIX, MCSTHRES, STEPSIZE
For SDUM
= anything except GLOBAL/GLOBEMF/GLOBHAD:
WHAT(1)
: controls the step optimisation for multiple Coulomb scattering
(see Note 1) and the number of (possible) single scatterings on a
material by material basis
<= -1.0 : a possible previous request of optimisation is cancelled
and the number of single scatterings in the materials
indicated by WHAT(4)
-WHAT(6)
is reset to the default value
(i.e. 0, or the global default possibly set previously by
the MULSOPT option with SDUM
= GLOBAL/GLOBHAD/GLOBEMF)
= 0.0 : ignored
= I0 + I1*10 + I2*100000
(with 0=< I0 =<1, 0=< I1 <10000, 0 =< I2 < 10000):
I0 >= 1 : the optimisation is activated
I1 - 1 = number of single scattering steps for hadrons and
muons in the materials indicated by WHAT(4)
to
WHAT(6)
I1 = 0 : ignored
I2 - 1 = number of single scattering steps for electrons and
positrons in the materials indicated by
WHAT(4)
-WHAT(6)
I2 = 0 : ignored
Default
: -1.0 (no multiple scattering optimisation and no single
scattering)
WHAT(2)
:
|WHAT(2)
| = 1.0: spin-relativistic corrections are activated for hadrons
and muons at the 1st Born approximation level
|WHAT(2)
| = 2.0: spin-relativistic corrections are activated for hadrons
and muons at the 2nd Born approximation level
WHAT(2)
< 0.0: nuclear finite size effects (form factors) are activated (see Note 2)
= -3.0: nuclear finite size effects are
considered but not the spin-relativistic effects
WHAT(2)
>= 3.0: multiple scattering for hadrons and muons is
completely suppressed (see Note 3)
Default
: 0.0 (no corrections)
WHAT(3)
:
|WHAT(3)
| = 1.0: spin-relativistic corrections are activated for e+ and e-
at the 1st Born approximation level
|WHAT(3)
| = 2.0: spin-relativistic corrections are activated for e+ and e-
at the 2nd Born approximation level
WHAT(3)
< 0.0: nuclear finite size effects are activated
WHAT(3)
>= 3.0: multiple scattering for e+ and e- is completely suppressed
(see Note 3)
Default
: 0.0 (no corrections)
WHAT(4)
= lower bound of the indices of the materials, or corresponding
name, in which the corrections are activated
("From material WHAT(4)
...")
Default
= 3.0
WHAT(5)
= upper bound of the indices of the materials, or corresponding
name, in which the corrections are activated
("... to material WHAT(5)
...")
Default
= WHAT(4)
WHAT(6)
= step length in assigning indices
("...in steps of WHAT(6)
")
Default
: 1.0
SDUM
= FANO-ON : Fano correction for inelastic interactions of charged
hadrons and muons on atomic electrons switched on
FANO-OFF: Fano correction for inelastic interactions of charged
hadrons and muons on atomic electrons is switched off
MLSH-ON : Original Molière screening angle on for hadrons and
muons
MLSH-OFF: Molière screening angle for hadrons and muons as
modified by Berger & Seltzer for electrons and
positrons (not recommended)
Default
: Fano correction on, original Molière screening angle
for hadrons on
Default
(option MULSOPT not given): no MCS optimisation
For SDUM
=GLOBAL/GLOBEMF/GLOBHAD: (GLOBEMF restricts the input value to
the EM part, GLOBHAD to charged hadrons and muons)
WHAT(1)
: controls the minimum MCS step size used by the boundary approach
algorithm for electrons/positrons and charged heavy
particles
0.2 > WHAT(1)
>= 0.0 : ignored
WHAT(1)
>= 0.2 : the minimum step size is set equal to the size
corresponding to B=5 in Molière theory, multiplied by
WHAT(1)
< 0.0 : the minimum step is reset to default
Default
: WHAT(1)
= 1 (maximum accuracy)
WHAT(2)
: index of step stretching factor tabulation to be used by the
electron/positron transport algorithm when approaching a
boundary.
ONLY FOR EXPERTS! NOT FOR THE NORMAL USER
The values of the index implemented for the moment are 1,2,3,4.
Values 11,12,13,14 cause the sensing algorithm to multiply
the range/mcs step rather than the current step.
Values 101,111,102,112,103,113,104,114 have the additional
effect of making the algorithm resample as unphysical any
step cut at a boundary and "reflected" from the boundary.
= 0.0 : ignored
< 0.0 : the tabulation index is reset to default
Default
: WHAT(2)
= 1 (maximum accuracy)
WHAT(3)
: controls the optimal step to be used by the optimisation option
(and to some extent by the hadron/muon boundary approach
algorithm).
ONLY FOR EXPERTS! NOT FOR THE NORMAL USER
0.2 > WHAT(3)
>= 0.0 : ignored
WHAT(3)
>= 0.2 : the minimum step size is set equal to the size
corresponding to B = 5 in Molière theory [Mol47,Mol48,
Mol55,Bet53], multiplied by WHAT(3)
< 0.0 : the minimum step is reset to its default value
Default
: minimum step equal to that corresponding to B=5,
multiplied by 20
WHAT(4)
> 0: single scattering option activated at boundaries or for too
short steps
< 0: resets to default
= 0: ignored
Default
: single scattering not activated
WHAT(5)
: (meaningful only if single scattering is activated at
boundaries and when step is too short: see WHAT(4)
above)
> 0: single scattering option activated for energies too small for
Molière theory to apply
< 0: not activated
= 0: ignored
Default
: not activated
WHAT(6)
: (meaningful only if single scattering is activated at boundaries
and when the step is too short: see WHAT(4)
above)
> 0: number of single scatterings to be performed when crossing a
boundary. To replace multiple scattering with single
scattering everywhere, see Note 5.
= 0: ignored
< 0: resets the default
Default
: 1
Notes:
1) When optimisation is requested, the program always makes the minimum
step for which the Molière theory of multiple scattering is
applicable. Optimisation via MULSOPT is available only for charged
hadrons and muons. For electrons and positrons, option EMFFIX is
recommended.
2) The correction for the nuclear finite size has been implemented
using simple Thomas-Fermi form factors according to Tsai [Tsa74].
The user can provide more sophisticated values by supplying a
function FORMFU which must return the square of the nuclear form
factor. (See details in 13}).
3) Complete suppression of multiple scattering can be useful in some
particular cases, for instance when replacing a gas of extremely low
density by a gas of the same composition but of much larger density
in order to increase the frequency of inelastic interactions or
bremsstrahlung reactions (of course, the results must then be scaled
by the density ratio). In such a case, one should also select the
biased density so that no re-interaction of secondaries can take
place.
4) Runs for which the nuclear form factor is taken into account
and/or the 2nd Born approximation is requested are very
CPU-time consuming at low energy (but not at high energy).
5) Setting WHAT(6)
> 1000.0 with SDUM
= GLOBAL, GLOBHAD or GLOBEMF,
replaces systematically multiple scattering with single scattering
everywhere. This choice is generally extremely demanding in CPU
time, except for particles of very low energy (a few keV), which
have a very short history anyway. In such cases, the single
scattering option is even recommended ([Fas01]).
Example 1 (number based):
MULSOPT 1.0 -1.0 2.0 5.0 15.0 5.0
The same example, name based:
MULSOPT 1.0 -1.0 2.0 BERYLLIU GOLD 5.0
Example 2:
MULSOPT 1.0 1.0 1.0 1.0 0.0 2. GLOBEMF
Example 3:
MULSOPT 0.0 0.0 0.0 1.0 1.0 99999999.GLOBAL
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