Sets the size of electron steps corresponding to a fixed fraction of the
total energy. The setting is done by material, giving as many EMFFIX
definitions as needed. Only meaningful when the EMF option has been
requested (explicitly or implicitly via option DEFAULTS).
See also EMF, FLUKAFIX, MULSOPT, STEPSIZE
WHAT(1) = index of the material concerned
WHAT(2) = maximum fraction of the total energy to be lost in a step
Default: 20% (it is strongly recommended not to set higher
than this value!)
WHAT(3) = same as WHAT(1); WHAT(4) = same as WHAT(2)WHAT(5) = same as WHAT(1); WHAT(6) = same as WHAT(2)SDUM = PRINT : electron and positron dE/dx and maximum allowed step
tabulations for this material are printed
= NOPRINT: tabulations are not printed (cancels any previous PRINT
request for the given materials)
= blank: ignored
Default: NOPRINT
Default (option EMFFIX not requested): the energy lost per step is 20% for
all materials
Notes:
1) The default provided (step length such that 20% of the energy is
lost) is acceptable for most routine problems.
In dosimetry problems and in thin-slab geometries it is recommended
not to exceed 5-10%.
For a detailed discussion of the step length problem, see [Fer91a].
2) Related options are STEPSIZE, MCSTHRES, FLUKAFIX and MULSOPT (see).
MCSTHRES and FLUKAFIX concern only heavy charged particles (hadrons
and muons), while STEPSIZE applies to ALL charged particles
(hadrons, muons and electrons). However, STEPSIZE defines the
steplength in cm and by region, while EMFFIX relates the step
length to the maximum allowed energy loss and is based on
materials. STEPSIZE works also in vacuum and is adapted to problems
with magnetic fields; if both options are used, the smallest of the
two steps is always chosen. Note however that if a step required by
STEPSIZE is too small for the Molière algorithm, multiple
scattering IS turned off (contrary to what happens with EMFFIX).
MULSOPT is very CPU-time consuming; however, it gives the highest
accuracy compatible with the Molière theory. It is used rarely,
mostly in low-energy and in backscattering problems.
Example:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...
MATERIAL 13. 26.98 2.6989 3. 0. 0. ALUMINUM
MATERIAL 82. 207.20 11.35 4. 0. 0. LEAD
MATERIAL 29. 63.546 8.96 12. 0. 0. COPPER
MATERIAL 6. 12.000 2.00 26. 0. 0. CARBON
MATERIAL 7. 14.000 0.0012 27. 0. 0. NITROGEN
MATERIAL 8. 16.000 0.0014 28. 0. 0. OXYGEN
MATERIAL 1. 1.000 0.0001 29. 0. 1. HYDROGEN
MATERIAL 0. 0.0 1.0000 30. 0. 0. TISSUE
COMPOUND 5.57E-3 26.0 1.118E-3 27. 2.868E-2 28. TISSUE
COMPOUND 6.082E-2 29.0 0. 0. 0. 0. TISSUE
EMFFIX 3. 0.15 4. 0.15 12. 0.15
EMFFIX 30. 0.05 0. 0. 0. 0. PRINT
* In this example, a maximum energy loss per step of 15% is requested
* for aluminium, copper and lead, while a more accurate 5% is requested
* for tissue
