13.2.6} fluscw.f: weighting fluence, current and yield

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     Argument list:
          IJ      : particle type (input only, cannot be modified)
          PLA     : particle momentum (if > 0), or -PLA = kinetic energy
                    (if < 0)
          TXX,TYY,TZZ: particle current direction cosines
          WEE     : particle weight
          XX,YY,ZZ: particle position
          NREG    : current region (after boundary crossing)
          IOLREG  : previous region (before boundary crossing). Useful only
                    whith boundary crossing estimators; for other estimators it
                    has no meaming.
          LLO     : particle generation (input only, cannot be modified)
          ICALL   : internal code calling flag (not for general use)

 Function FLUSCW is activated by option USERWEIG, with 
WHAT(3)
 > 0.0.
 Yields obtained via USRYIELD, fluences calculated with USRBDX,
 USRTRACK, USRCOLL, USRBIN, and currents calculated with USRBDX are
 multiplied by the value returned by this function. The user can
 implement any desired logic to differentiate the returned value
 according to any information contained in the argument list (particle
 type, energy, direction, weight, position, region, boundary, particle
 generation), or information available in the SCOHLP COMMON block
 (binning or detector number, estimator type).
 The scored quantity is given by the flag ISCRNG (in SCOHLP):
          ISCRNG = 1 --> Boundary crossing estimator
          ISCRNG = 2 --> Track  length     binning
          ISCRNG = 3 --> Track  length     estimator
          ISCRNG = 4 --> Collision density estimator
          ISCRNG = 5 --> Yield             estimator
 The binning/detector number is given by JSCRNG (in SCOHLP) and is
 printed in output:
          Bdrx n. 2  "bdxname" , generalised particle n. 8,
                                            from region n. 22 to region n. 78
          Track n. 6  "trkname" , generalised particle n. 14, region n.   9.
 Note that a track-length detector can have the same JSCRNG number as
 a boundary crossing one or a binning etc. (use the value of ISCRNG to
 discriminate).
 Further information can be obtained including COMMON TRACKR (for
 instance particle age). TRACKR contains also special user variables
 (both integer and in double precision) which can be used to save
 information about particles which have undergone some particular event.
 Function FLUSCW has many applications. A common one is conditional scoring
 (score only if within a certain distance from a point, etc.): for instance it
 is possible to implement a sort of 2-dimensional fluence binning on a plane
 boundary.

 FLUSCW can be used also when scoring "fluxes" (i.e. fluences or
 currents or yields) of heavy ions, to discriminate between different
 types of ions.
 All ions in FLUKA carry the same id-number IJ = -2: therefore ion
 fluxes obtained by the various estimators will refer to all ions
 unless an additional discrimination is introduced by the user at
 scoring time. This can be done in FLUSCW as follows:
                   CALL USRDCI(IJ,IONA,IONZ,IONM)
        The three integer values returned are the following ion properties:
          IONA = mass number of the ion
          IONZ = atomic number
          IONM = flag for isomeric state
        Based on their values, the user can decide or not to accept the
        scoring.

 Other interesting applications are based on the fact that
 FLUSCW is called at every boundary crossing, provided that at least
 one USRBDX detector has been requested. Although the function has
 been designed mainly to weight scored quantities, it can be "cheated"
 to do all sorts of side things, even not directly connected with
 scoring. Note that the variables in the argument list, with the
 exception of IJ, LLO and ICALL, are local copies of those used for
 particle transport, and therefore can be modified to have an effect
 on scoring, without affecting transport.

 If name-based input is being used, the name corresponding to NREG and IOLREG
 can be obtained via a call to routine GEOR2N:
           CALL GEOR2N (NUMREG, NAMREG, IERR)
 where NUMREG (input variable) is the region number, and NAMREG
 (returned variable) is the corresponding region name (to be declared
 as CHARACTER*8). IERR is a returned error code: if = 0, the
 conversion is successful. See example in the description of BXDRAW below.

 
Note:
 setting the variable LSCZER (in SCOHLP) = .TRUE. before
       RETURN, will cause zero scoring whatever the value returned
       by FLUSCW. This is more efficient than returning a zero value.

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