EMFFIX¶

Summary

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 or name 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

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].
Related options are STEPSIZE, MCSTHRESh, FLUKAFIX and MULSOPT. MCSTHRESh and FLUKAFIX concern only heavy charged particles (hadrons and muons), while STEPSIZE applies to all charged particles (hadrons, muons, electrons and positrons). 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 (number based):

*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...
MATERIAL         13.       0.0    2.6989        3.        0.       0. ALUMINUM
MATERIAL         82.       0.0     11.35        4.        0.       0. LEAD
MATERIAL         29.       0.0      8.96       12.        0.       0. COPPER
MATERIAL          6.       0.0      2.00       26.        0.       0. CARBON
MATERIAL          7.       0.0    0.0012       27.        0.       0. NITROGEN
MATERIAL          8.       0.0    0.0014       28.        0.       0. OXYGEN
MATERIAL          1.       0.0    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

The same example, name based:

*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...
MATERIAL         13.       0.0    2.6989       0.0        0.       0. ALUMINUM
MATERIAL         82.       0.0     11.35       0.0        0.       0. LEAD
MATERIAL         29.       0.0      8.96       0.0        0.       0. COPPER
MATERIAL          6.       0.0      2.00       0.0        0.       0. CARBON
MATERIAL          7.       0.0    0.0012       0.0        0.       0. NITROGEN
MATERIAL          8.       0.0    0.0014       0.0        0.       0. OXYGEN
MATERIAL          1.       0.0    0.0001       0.0        0.       1. HYDROGEN
MATERIAL          0.       0.0    1.0000        0.        0.       0. TISSUE
COMPOUND     5.57E-3    CARBON  1.118E-3  NITROGEN  2.868E-2   OXYGEN TISSUE
COMPOUND    6.082E-2  HYDROGEN        0.        0.        0.       0. TISSUE
EMFFIX      ALUMINUM      0.15      LEAD      0.15    COPPER     0.15
EMFFIX        TISSUE      0.05        0.        0.        0.       0. PRINT