WW–THRESh¶

Summary

Defines the energy limits for a Russian Roulette/splitting weight window and applies particle-dependent modification factors to the windows defined by WW–FACTOr

See also BIASING, WW–FACTOr, WW–PROFIle

WHAT(1) > 0.0:: upper kinetic energy threshold in GeV for Russian Roulette (RR)/Splitting with a weight window. For low-energy neutrons, corresponding (smallest) group number (included)
= 0.0:: ignored
< 0.0:: any previously selected threshold is cancelled
WHAT(2) ≥ 0.0: and < WHAT(1): lower kinetic energy threshold in GeV for RR/Splitting with a weight window. For low-energy neutrons, corresponding (largest) group number (included)
< 0.0: or > WHAT(1): WHAT(2) is set = WHAT(1)
WHAT(3) > 0.0:: amplification factor used to define the weight window width at the higher energy threshold represented by WHAT(1). The weight window at the higher energy threshold is obtained by multiplying by WHAT(3) the top edge of the window (splitting level) at the lower threshold, and dividing by the same factor the bottom edge (RR-level)
< 0.0:: |WHAT(3)| is used as a multiplication factor for the bottom and top levels of every region for the particles selected by WHAT(4–6). That is, for such particles both bottom and top are multiplied by |WHAT(3)|
Default: = 10.0 (amplification factor for the splitting and RR-level at the higher threshold). The particle dependent multiplication factor by default is set = 1.0
WHAT(4) =: lower bound of the particle numbers (or corresponding particle name) to which the indicated weight window energy limits apply. Note that particle number 40.0 indicates low-energy neutrons (for this purpose only!). Particle number 8.0 indicates neutrons with energy > 20 MeV

(“From particle ``WHAT(4)``…”)
Default: = 1.0
WHAT(5) =: upper bound of the particle numbers (or corresponding particle name) to which the indicated weight window energy limits apply

(“…to particle ``WHAT(5)``…”)
Default: = WHAT(4) if WHAT(4)> 0.0, all particles otherwise
WHAT(6) =: step length in assigning numbers

(”…in steps of ``WHAT(6)`` ”)
Default: = 1.0
SDUM = PRIMARY:: the weight window applies also to primary particles
= NOPRIMARy:: the weight window doesn’t apply to primaries
Default: = PRIMARY
Default: : (option WW–THRESh or WW–FACTOr not given): no weight window is defined

Notes

Option WW–THRESh is only meaningful when WW-FACTOr (WW–FACTOr) is also requested. See Note 1 to that option for more information.
For low-energy neutrons, the two energy thresholds are expressed as group numbers, while for all other particles (including high-energy neutrons) they are expressed in GeV. Therefore, thresholds for low-energy neutrons must be assigned in a separate WW–THRESh card from other particles.

Example (number based):

*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...+...8
WW-THRESh        2.0      0.05       2.4       3.0       7.0       0.0
*  The weight window weight limits for particles 3 to 7 (practically electrons,
*  positrons and photons, since neutrinos are discarded), which have been set
*  by WW-FACTOr are applied as such below 50 MeV. Above that energy, the width
*  of the window is progressively increased up to 2 GeV: at 2 GeV, the upper
*  weight limit is a factor 2.4 larger and the lower limit a factor 2.4
*  smaller.

The same example, name based:

WW-THRESh        2.0      0.05       2.4  ELECTRON    PHOTON       0.0