defines extra factors dependent on energy group ("profiles"), to
modify the basic setting of the low-energy neutron weight-windows in
selected sets of regions, or the low-energy neutron importances in
each region
(see also BIASING, WW-FACTOr, WW-THRESh)
WHAT(1) = weight-window extra factor for the profile defined by
WHAT(6), concerning the energy groups defined by WHAT(3),
WHAT(4) and WHAT(5) (both the top and bottom window levels
will be multiplied by WHAT(1))
= 0.0 : ignored
< 0.0 : resets to default (extra factor = 1.0)
Default = 1.0 (windows are not modified)
WHAT(2) = importance extra factor. See Note below.
= 0.0 : ignored
< 0.0 : resets to default (extra factor = 1.0)
Default = 1.0 (importances are not modified)
WHAT(3) = lower bound of the group number for which the extra factor
WHAT(1) or WHAT(2) is requested ("From group WHAT(3)...")
Default = 1.0 (the group of highest energy)
WHAT(4) = upper bound of the group numbers for which the extra
factor WHAT(1) or WHAT(2) is requested ("...to group
WHAT(4)...")
Default = WHAT(3)WHAT(5) = step length in assigning group numbers ("...in steps of
WHAT(5)").
Default = 1.0
WHAT(6) = profile number defined by WHAT(1), WHAT(3-5) (up to 5
different profiles are allowed).
Default: profile number 1.
SDUM : not used
Default (option WW-PROFIle not given): 1.0 (no extra factor)
Note: This option applies only to low-energy neutrons. It is used
to refine the basic bias setting defined by two other
options: WW-FACTOr and BIASING.
WHAT(1) refers to WW-FACTOr: it allows the user to tune the
weight window by energy group (WW-FACTOr does the same by
region). The profile defined will be applied to raise or
lower the weight-window levels (for low-energy neutrons only)
in a group of regions selected by means of WHAT(4-6) and SDUM
in option WW-FACTOr.
WHAT(2) refers to BIASING: its aim is to define a reference
weight level in each region, which is used by the program to
avoid excessive biasing in some critical cases. If the user
has defined a weight-window (options WW-FACTOr and WW-THRESh), the
reference weight level is not needed because it is derived directly
from the window parameters. If the user has not defined a
weight-window but has defined region importances (option
BIASING), the reference weight level for a region is assumed
in most cases to be the inverse of the corresponding
importance. However, since importance biasing is not based on
absolute values of importance but on importance ratios, in
some rare cases the user may give importances which are not
equal to the inverse of the average particle weight, but only
proportional to it. (This is in order to better exploit the
full importance range, since for technical reasons in FLUKA
allowed importance values range only from 0.0001 to 10000.).
In such cases it is possible to multiply all the importances
by a factor WHAT(2) ONLY FOR THE PURPOSE OF CALCULATING THE
REFERENCE WEIGHT LEVEL.
Modification of importances by a factor WHAT(2) apply to
ALL regions (but only for low-energy neutrons).
If neither weight-window nor importances have been given,
FLUKA still calculates a weight reference level from the ratio
of physical to biased non-absorption probability. If a
particle's weight exceeds the reference level in a given
region by more than a factor calculated at run time, non-absorption
probability biasing is switched off and transport continues according
to the physical absorption probabilities (analogue transport).
Example 1:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...+...8
WW-PROFIle 0.9 0.0 1. 11. 0.0 4.0
WW-PROFIle 0.7 0.0 12. 70. 0.0 4.0
WW-PROFIle 0.5 0.0 71. 72. 0.0 4.0
* Profile n. 4 is defined a multiplication factor for weight windows, where
* the upper and the lower weight limits (as defined by WW-FACTOr and
* WW-THRESh) are multiplied by 0.9 for the first 11 neutron groups, by 0.7
* for groups 12 to 70, and by 0.5 for groups 71 and 72.
Example 2:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...+...8
WW-PROFIle 0.0 1.8 1. 65. 0.0 2.0
WW-PROFIle 0.0 2.3 66. 72. 0.0 2.0
* Profile n. 2 is defined a multiplication factor for importances, where
* the importances (as defined by BIASING) are multiplied by 1.8 for the first
* 65 neutron groups, and by 2.3 for groups 66 to 72.
