Last version:
FLUKA 2021.2.1, July 26th 2021
(last respin )
flair-2.3-0b 30-Jul-2021

News:

-- Fluka Release
( 30.07.2021 )

FLUKA 2021.2.1 has been released.
Fluka Major Release 18.05.2021 FLUKA 2021.2.0 has been released.
Congratulations from INFN: ,
Dear Paola,
I wish to congratulate you and all the authors and collaborators for this new Fluka release, which looks at the future and confirms the support of INFN in the development and continuous improvement of this code.
best regards
Diego Bettoni
INFN Executive Committee


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13 User routines

Unlike some other Monte Carlo particle transport codes, FLUKA gets its input mainly from a simple file. It offers a rich choice of options for scoring most quantities of possible interest and for applying different variance reduction techniques, without requiring the user to write a single line of code. However, although normally there is no need for any "user code", there are special cases where this is unavoidable, either because of the complexity of the problem, or because the desired information is too unusual or too problem-specific to be offered as a standard option. And on the other hand, even when this is not strictly necessary, experienced programmers may like to create customised input/output interfaces. A number of user routines (available on LINUX and UNIX platforms in directory usermvax) allow to define non-standard input and output, and in some cases even to modify to a limited extent the normal particle transport. Most of them are already present in the FLUKA library as dummy or template routines, and require a special command in the standard input file to be activated. Users can modify any one of these routines, and even insert into them further calls to their own private ones, or to external packages (at their own risk!). This increased flexibility must be balanced against the advantage of using as far as possible the FLUKA standard facilities, which are known to be reliable and well tested.

To implement their own code, users must perform the following steps:

  • 1) make a modified copy of one or more of these routines. It is recommended that each modified routine should always print an informative message when called for the first time, to confirm that it has been successfully activated, for future documentation, and to avoid misinterpretations of the standard output. It is important to remember that when calling modified user routines, the units, titles etc. reported in the normal FLUKA output become often meaningless.

A typical way to do this is:

       ..............
       LOGICAL LFIRST
       SAVE LFIRST
       DATA LFIRST /.TRUE./
 * return message from first call
       IF (LFIRST) THEN
          WRITE(LUNOUT,*) 'Version xxx of Routine yyy called'
          LFIRST = .FALSE.
       ENDIF
       ..............

IMPORTANT: The user should not modify the value of any argument in a routine calling list, except when marked as "returned" in the description of the routine here below. Similarly, no variable contained in COMMON blocks should be overwritten unless explicitly indicated.

  • 2) compile the modified routines (with the fff script on LINUX/UNIX):
         fff yyy.f  (produces a new file yyy.o)

  • 3) link them (with the lfluka script on LINUX/UNIX) to the FLUKA library and any additional library of interest (for instance CERNLIB):
         lfluka -o myfluka -m fluka yyy.o

This will produce a new executable (indicated here as myfluka). To run the new executable, launch the usual rfluka script with the option -e myfluka.

13.1 INCLUDE files

It is recommended that at least the following lines be present at the beginning of each routine:

       INCLUDE '(DBLPRC)'
       INCLUDE '(DIMPAR)'
       INCLUDE '(IOUNIT)'

Each INCLUDE contains a COMMON block, plus related constants. Additional INCLUDEs may be useful, in particular BEAMCM, CASLIM, EMFSTK, SOURCM, EVTFLG, FHEAVY, GENSTK, LTCLCM, FLKMAT, RESNUC, SCOHLP, SOUEVT, FLKSTK, SUMCOU, TRACKR, USRBIN, USRBDX, USRTRC, USRYLD.

Files flukaadd,add and emfadd.add contain a full documentation about the meaning of the variables of these INCLUDE files.

Here is a summary of their content:

  DBLPRC: included in ALL routines of FLUKA, contains the declaration
          IMPLICIT DOUBLE PRECISION (A-H,O-Z)
          and sets many mathematical and physical constants. Users are strongly
          encouraged to adhere to "FLUKA style" by using systematically double
          precision (except for very good reasons such as calling external single
          precision scoring packages), and to use constants defined in this file
          for maximum accuracy.
  DIMPAR: dimensions of the most important arrays
  IOUNIT: logical input and output unit numbers

  BEAMCM: properties of primary particles as defined by options BEAM
          and BEAMPOS
  CASLIM: number of primary particles followed (needed for normalisation)
  EMFSTK: particle stack for electrons and photons
  SOURCM: user variables and information for a user-written source
  EVTFLG: event flags (still undocumented)
  FHEAVY: stack of heavy secondaries created in nuclear evaporation
  GENSTK:  properties of each secondary created in a hadronic event
  LTCLCM: LaTtice CeLl CoMmon (needed when writing symmetry transformations for
          Lattice Geometry)
  FLKMAT:   material properties
  RESNUC: properties of the current residual nucleus
  SCOHLP: SCOring HeLP (information on current detector and estimator type). It
          contains a flag ISCRNG, indicating the quantity being scored by the
          current binning or the estimator corresponding to the current
          detector, and one JSCRNG corresponding to the binning/detector number.
          Binnings and detectors are sequentially numbered according to their
          order of appearance in standard input. Note that detectors
          corresponding to different estimators can have the same JSCRNG number
          (for instance Binning N. 3 and Tracklength detector N. 3). They can be
          distinguished based on the value of ISCRNG. However, note that the
          same value of ISCRNG may have different meanings in functions FLUSCW
          and COMSCW.
  SOUEVT: SOUrce EVenT (useful when source particles are obtained from an
          external event generator)
  FLKSTK:  main FLUKA particle stack
  SUMCOU: total numbers and total weights relative to many physical and Monte
          Carlo events (needed for normalisation, energy balance etc.)
  TRACKR: TRACKs Recording (properties of the currently transported particle and
          its path)
  USRBIN, USRBDX, USRSNC, USRTRC, USRYLD: parameters of the requested estimator
          detectors and binnings

13.2 User routines


13.2.1 abscff.f: user defined ABSorption CoeFFicient

Argument list (all variables are input only):

          WVLNGT : photon wavelength (in cm)
          OMGPHO : angular frequency (omega = 2pi nu) of the photon (in s-1)
          MMAT   : material index

Function ABSCFF returns a user-defined absorption coefficient for optical photons. It is activated by setting WHAT(2) < -99 in command OPT-PROP, with SDUM = blank. See option OPT-PROP and Chap. (12) for more information.


13.2.2 comscw.f: weighting deposited energy, stars or residual nuclei

Argument list:

          IJ    : particle type (1 = proton, 8 = neutron, etc.: see code in (5))
                  Input only, cannot be modified.
          XA,YA,ZA : current particle position
          MREG  : current geometry region
          RULL  : amount to be deposited (unweighted)
          LLO   : particle generation. Input only, cannot be modified.
          ICALL : internal code calling flag (not for general use)

This routine is activated by option USERWEIG, with WHAT(6) > 0.0. Energy and star densities obtained via SCORE and USRBIN, and energy and stars obtained via EVENTBIN and production of residual nuclei obtained via RESNUCLEi 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, position, region, amount deposited, particle generation), or information available in the SCOHLP COMMON block (binning number, type of scored quantity). The scored quantity is given by the flag ISCRNG (in SCOHLP):

    ISCRNG = 1 --> Energy density  binning
    ISCRNG = 2 --> Star   density  binning
    ISCRNG = 3 --> Residual nuclei scoring

The binning/detector number is given by JSCRNG (in SCOHLP) and is printed in output:

    Res. nuclei n. 3  äny-name" , "high" energy products, region n. 4
    R-Phi-Z  binning n. 5  öther-name" , generalised particle n.    1

Note that a detector of residual nuclei can have the same JSCRNG number as a binning (use the value of ISCRNG to discriminate). Further information can be obtained including COMMON TRACKR (for instance particle's total energy, direction cosines, 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. If data concerning the current material are needed, it can be accessed as MEDIUM(MREG) if file (FLKMAT) is included. Indeed, a common simple application of COMSCW is to score dose according to the local density (especially useful to get the correct average dose in bins straddling a boundary between two different media):

          ..................
          INCLUDE '(FLKMAT)'
          INCLUDE '(SCOHLP)'
          ..................
 * ========== In order to compute doses ========= *
 *        Medium(n) is the material number of region n
 *        Rho(m) is the density of material m (in g/cm3)
 *        Iscrng = 1 means we are depositing energy (not stars)
          IF ( ISCRNG .EQ. 1 ) THEN
 *           to get dose in Gy (elcmks is the electron charge in C)
             COMSCW = ELCMKS * 1.D12 / RHO (MEDIUM(MREG))
          ELSE
 *           oneone is defined as 1.D0 in include DBLPRC
             COMSCW = ONEONE
          ENDIF
          ..................

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.

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


13.2.3 dffcff.f: user defined DiFFusion CoeFFicient

Argument list (all variables are input only):

          WVLNGT : photon wavelength (in cm)
          OMGPHO : angular frequency (omega = 2pi nu) of the photon (in s-1)
          MMAT   : material index

Function DFFCFF returns a user-defined diffusion coefficient for optical photons. It is activated by setting WHAT(3) < -99 in command OPT-PROP, with SDUM = blank. See option OPT-PROP and Chap. (12) for more information.


13.2.4 endscp.f: ENergy density DiStributed - Change of Positions

Argument list (all variables are input only):

          IJ     : particle type (input only)
          NTRUCK : number of step points (input only)
          XTRUCK,YTRUCK,ZTRUCK : particle step points, can be modified by user
          MREG   : region number (input only)
          LLO    : particle generation (input only)
          ICALL  : internal code calling flag (not for general use)

Subroutine ENDSCP allows to shift by a user-defined distance the energy which is being deposited along a step or several step binning portions, by providing new segment endpoints. A typical application is to simulate an instrument drift.


13.2.5 fldscp.f: FLuence DiStributed - Change of Positions

Argument list (all variables are input only):

          IJ     : particle type
          PLA    : particle momentum (if > 0), or kinetic energy (if < 0)
                   (input only)
          TXX,TYY,TZZ : particle direction cosines, can be modified by user
          NTRUCK : number of step points
          XTRUCK,YTRUCK,ZTRUCK : particle step points, can be modified by user
          NREG   : new region number (input only)
          IOLREG : old region number (input only)
          LLO    : particle generation (input only)
          ICALL  : internal code calling flag (not for general use)

Subroutine FLDSCP allows to shift by a user-defined distance the track whose length is being scored as fluence along a step or several step binning portions, by providing new segment endpoints. A typical application is to simulate an instrument drift.


13.2.6 fluscw.f: weighting fluence, current and yield

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 in shielding calculations is to multiply selected scored fluences by particle/energy-dependent fluence-to-dose equivalent conversion coefficients, or by some instrument response, radiation damage curve, etc. A version of FLUSCW converting particle fluences to various forms of dose equivalent and effective dose is available in file deq99.f, in the $FLUPRO/flutil directory. Instructions for its use are contained in the comment lines at the beginning of the file.

Another application 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.

 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.


13.2.7 formfu.f nuclear form factor

Argument list (all variables are input only):

          IJ     : particle code, except that it is set to 3 for both e+ and e-
          QU2    : squared momentum transfer (GeV/c)^2
          ZMEDIU : atomic number of target nucleus
          AMEDIU : atomic mass of target nucleus

Function FORMFU can be used to override the standard value of the nuclear charge form factor. It must return the squared value of the nuclear charge form factor for particle IJ. The default version computes the form factor in Born approximation for a medium of given composition, using the simple expression given by Tsai [Tsa74], and accounts also for the contribution of incoherent scattering. The function is called by the multiple and single scattering routines if option MULSOPT has been issued with WHAT(3) <t 0.0 for electrons and positrons, and WHAT(2) < 0.0 for hadrons and muons. See Note 2) to option MULSOPT.


13.2.8 frghns.f material roughness (for optical photons)

Argument list (all variables are input only):

          TXX, TYY, TZZ : particle direction cosines
          UXSRFC, UYSRFC, UZSRFC: direction of the normal to the surface
          MREG          : region the particle is coming from
          NEWREG        : region the particle is going to
          MMAT          : material the particle is coming from
          MMATNW        : material the particle is going to

Function FRGHNS can be used to return a non-zero value for the roughness of a boundary between two materials, relevant for optical photon transport (default roughness is zero for all boundaries). Meaningful only if options OPT-PROP or OPT-PROD have been requested.


13.2.9 musrbr.f 1st user defined quantity for special binning lusrbl.f 2nd user defined quantity for special binning fusrbv.f 3rd user defined quantity for special binning

These three functions are used to define 3-dimensional fluence distributions to be calculated by special user-defined binnings (see USRBIN with WHAT(1) = 8.0 in the first card).

  • MUSRBR defines a discrete (integer) variable (by default: region number).

Argument list (all variables are input only):

          IJ       : particle type
          PCONTR   : particle momentum
          XA,YA,ZA : particle position
          MREG     : current region
          LATCLL   : current lattice cell
          ICALL    : internal code calling flag (not for general use)

  • LUSRBL defines another discrete (integer) variable (by default:
    lattice number)

Argument list: same as for MUSRBR above

  • FUSRBV defines a continuous (double precision) variable (by default: pseudorapidity with respect to the Z axis)

Argument list: same as for MUSRBR above (except LATCLL)

The 3 functions are called at tracklength events. What is scored is the particle track-length multiplied by the particle's weight, possibly modified by a user-written FLUSCW (see above).


13.2.10 lattic.f (symmetry transformation for lattice geometry)

Subroutine LATTIC is activated by one or more LATTICE cards in the geometry input (see (8)). It is expected to transform coordinates and direction cosines from any lattice cell (defined by card LATTICE) to the reference system in which the basic structure has been described. The user is expected to provide a transformation of coordinates and vector direction cosines from each lattice cell to the corresponding basic structure (in ENTRY LATTIC) and of direction cosines from the basic structure to each corresponding lattice cell (in ENTRY LATNOR).

Entries:

  • LATTIC (position and direction symmetry transformation from lattice cell to prototype structure)

Argument list:

          XB(1), XB(2), XB(3) : actual physical position coordinates in IRLTGG
                                lattice cell
          WB(1), WB(2), WB(3) : actual physical direction cosines in IRLTGG
                                lattice cell
          DIST                : current step length
          SB(1), SB(2), SB(3) : transformed coordinates in prototype cell
          UB(1), UB(2), UB(3) : transformed cosines in prototype cell
          IR                  : region number in prototype cell
          IRLTGG              : lattice cell number
          IRLT                : array containing region indices corresponding to
                                lattice cells
          IFLAG               : reserved variable

LATTIC returns the tracking point coordinates (SB) and direction cosines(UB) in the reference prototype geometrical structure, corresponding to real position/direction XB, WB in the actual cell IRLTGG (defined as input region IR by a LATTICE card). When the lattice option is activated, the tracking proceeds in two different systems: the "real" one, and that of the basic symmetry unit. Particle positions and directions are swapped from their real values to their symmetric ones in the basic cell, to perform the physical transport in the regions and materials that form the prototype geometrical structure and back again to the real world. The correspondence between "real" and "basic" position/direction depends on the symmetry transformation and on the lattice cell number.

  • LATNOR (LATtice cell NORmal transformation from prototype structure to lattice cell)

Argument list:

          UN(1), UN(2), UN(3) : direction cosines of the vector normal to the
                                surface, in the prototype cell (entry values)
                                and in the lattice cell (returned values)
          IRLTNO              : present lattice cell number

Entry LATNOR transforms the direction cosines stored in the vector UN(3) from the system of the basic prototype unit to that of the real world in lattice cell number IRLTNO. Therefore, this cosine transformation must be the inverse of that performed on the cosines by the LATTIC entry: but while LATTIC maps vector UB to a different vector WB, LATNOR maps the UN vector to itself. Note that if the transformation implies a rotation, it is necessary to save first the incoming UN cosines to local variables, to avoid overwriting the vector before all transformation statements are executed.

Notes:

     Different symmetry transformations can of course be implemented
     in the same LATTIC routine (each being activated by a different cell
     number or range of cell numbers).
     The advantage of the lattice geometry is to avoid describing in detail
     the geometry of repetitive multi-modular structures. It must be
     realised, however, that a penalty is generally paid in computer efficiency.
     Also, a region contained in the prototype cell and all those "mapped"
     to it inside lattice cells are treated by the program as if they
     were connected with "non-overlapping ORs" into a single region.
     Therefore, any region-based scoring (options SCORE, USRTRACK, etc.)
     can only provide quantities averaged over the whole structure. More
     detailed information must be obtained by region-independent options
     such as USRBIN or by user-written routines (MGDRAW).
     The USRBIN and EVENTBIN options, with WHAT(1) = 8, can also be used
     to request a special binning type which activates the MUSRBR,
     LUSRBL, FUSRBV user routines to recover lattice information (see
     routine musrbr.f below)
     A transformation between a lattice cell and a prototype region can
     alternatively be defined without resorting to the LATTIC user routine.
     In this case, the transformation is defined via a ROT-DEFIni card and
     the correspondence is established by giving the transformation index
     in the SDUM of the LATTICE card (see  Chap. (8)).


13.2.11 magfld.f definition of a magnetic field

Argument list:

          X,Y,Z       : current position (input only)
          BTX,BTY,BTZ : direction cosines of the magnetic field vector
                        (returned).
          B           : magnetic field intensity in Tesla (returned)
          NREG        : current region (input only)
          IDISC       : if returned = 1, the particle will be discarded

MAGFLD is activated by option MGNFIELD with WHAT(4-6) = 0.0 and is used to return intensity and direction of a magnetic field based on the current position and region. It is called only if the current region has been flagged as having a non-zero magnetic field by option ASSIGNMAt, with WHAT(5) = 1.0. The magnetic field spatial distribution is often read and interpolated from an external field map. Note that in any case the direction cosines MUST be properly normalised in double precision (e.g. BTX = SQRT(ONEONE - BTY**2 - BTZ**2)), even if B = 0.0. Please read carefully the notes on option MGNFIELD.


13.2.12 mdstck.f management of the stack of secondaries

Argument list:

          IFLAG  : type of nuclear interaction which has produced secondaries:
                   1 : inelastic
                   2 : elastic
                   3 : low-energy neutron
          NUMSEC : number of secondary particles produced in the interaction

MDSTCK is called after a nuclear interaction in which at least one secondary particle has been produced, before any biasing is applied to decide which secondary will be loaded in the main stack for further transport. The properties of the secondaries are stored in the secondary stack (COMMON GENSTK). With MDSTCK, the user can analyse those secondaries, write them to a file, or even modify the content of GENSTK (for instance applying his own biasing). In the latter case, however, it is his responsibility to make sure that energy is conserved, the various physical quantities are still consistent, etc.


13.2.13 mgdraw.f general event interface

Subroutine MGDRAW, activated by option USERDUMP with WHAT(1) >= 100., usually writes a "collision tape", i.e. a file where all or selected transport events are recorded. The default version (unmodified by the user) offers several possibilities, selected by WHAT(3) in USERDUMP. Details are given in (11). Additional flexibility is offered by a user entry USDRAW, selected by WHAT(4) in USERDUMP, interfaced with the most important physical events happening during particle transport. The user can modify of course also any other entry of this subroutine (BXDRAW called at boundary crossings, EEDRAW called at event end, MGDRAW for trajectory drawing, ENDRAW for recording of energy depositions and SODRAW for recording of source events: for instance the format of the output file can be changed, and different combinations of events can be written to file.

No information is written by default at EEDRAW and BXDRAW calls, but the entries are called for any value of WHAT(3) in USERDUMP (EEDRAW also for WHAT(4) >= 1). But the most interesting aspect of the routine is that the five entries (all of which, if desired, can be activated at the same time by setting USERDUMP with WHAT(3) = 0.0 and WHAT(4) >= 1.0) constitute a complete interface to the whole FLUKA transport. Therefore, MGDRAW can be used not only to write a collision tape, but to do any kind of complex analysis (for instance studying correlations between events).

Entries:

  • MGDRAW (trajectory dumping for drawing)

Argument list (all variables are input only):

          ICODE : FLUKA physical compartment originating the call
                   = 1: call from Kaskad (hadrons and muons)
                   = 2: call from Emfsco (electrons, positrons and photons)
                   = 3: call from Kasneu (low-energy neutrons)
                   = 4: call from Kashea (heavy ions)
                   = 5: call from Kasoph (optical photons)
          MREG  : current region

MGDRAW writes by default, for each trajectory, the following variables (contained in COMMON TRACKR):

      NTRACK : number of track segments
      MTRACK : number of energy deposition events along the track
      JTRACK : type of particle
      ETRACK : total energy of the particle
      WTRACK : weight of the particle
      Ntrack values of XTRACK, YTRACK, ZTRACK : end of each track segment
      Mtrack values of DTRACK : energy deposited at each deposition event
      CTRACK : total length of the curved path

Other variables are available in TRACKR (but not written by MGDRAW unless the latter is modified by the user: particle momentum, direction cosines, cosines of the polarisation vector, age, generation, etc. (see a full list in the comment in the INCLUDE file).

  • BXDRAW (boundary crossing dumping)

Argument list (all variables are input only):

          ICODE  : FLUKA physical compartment originating the call
                    = 19: call from Kaskad (hadrons and muons)
                    = 29: call from Emfsco (electrons, positrons and photons)
                    = 39: call from Kasneu (low-energy neutrons)
                    = 49: call from Kashea (heavy ions)
                    = 59: call from Kasoph (optical photons)
          MREG   :   number of region before boundary crossing
          NEWREG : number of region after boundary crossing
          XSCO, YSCO, ZSCO : coordinates of crossing point

BXDRAW is called at each boundary crossing (if requested by the user with USERDUMP, WHAT(3) < 7.0). There is no default output: any output must be supplied by the user.

If name-based input is being used, the names corresponding to MREG and NEWREG can be obtained via a call to routine GEOR2N:

            CALL GEOR2N (NUMREG, NAMREG, IERR)

where NUMREG (input variable) is a 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. Example:

            .......................................
            CHARACTER*8 MRGNAM, NRGNAM
            .......................................
            ENTRY BXDRAW ( ICODE, MREG, NEWREG, XSCO, YSCO, ZSCO )
            CALL GEOR2N ( MREG,   MRGNAM, IERR1 )
            CALL GEOR2N ( NEWREG, NRGNAM, IERR2 )
            IF(IERR1 .NE. 0 .OR. IERR2 .NE. 0) STOP "Error in name conversion"
            .......................................
            IF(MRGNAM .EQ. "MyUpsREG" .AND. NRGNAM .EQ. "MyDwnREG") THEN
            .......................................

  • EEDRAW (event end)

Argument list:

          ICODE = -1: event not completed
                =  0: normal event termination
                =  4: stack overflow

EEDRAW is called at the end of each event, or primary history, (if requested by the user with USERDUMP, WHAT(3) =< 0.0). There is no default output: any output must be supplied by the user.

  • ENDRAW (energy deposition dumping)

Argument list (all variables are input only):

          ICODE : type of event originating energy deposition
                  1x: call from Kaskad (hadrons and muons)
                     10: elastic interaction recoil
                     11: inelastic interaction recoil
                     12: stopping particle
                     13: pseudo-neutron deposition
                     14: particle escaping (energy deposited in blackhole)
                     15: time kill
                  2x: call from Emfsco (electrons, positrons and photons)
                     20: local energy deposition (i.e. photoelectric)
                     21 or 22: particle below threshold
                     23: particle escaping (energy deposited in blackhole)
                     24: time kill
                  3x: call from Kasneu (low-energy neutrons)
                     30: target recoil
                     31: neutron below threshold
                     32: neutron escaping (energy deposited in blackhole)
                     33: time kill
                  4x: call from Kashea (heavy ions)
                     40: ion escaping (energy deposited in blackhole)
                     41: time kill
                     42: delta ray stack overflow
                  5x: call from Kasoph (optical photons)
                     50: optical photon absorption
                     51: optical photon escaping (energy deposited in
                         blackhole)
                     52: time kill
          MREG : current region
          RULL : energy amount deposited
          XSCO, YSCO, ZSCO : point where energy is deposited

ENDRAW writes by default, for each energy deposition point:

      0       : flag identifying ENDRAW output from that of other entries
      ICODE   : see argument list
      JTRACK, ETRACK, WTRACK : see MGDRAW above
      XSCO, YSCO, ZSCO, RULL : see argument list

  • SODRAW (source particle dumping)

No arguments

SODRAW writes by default, for each source or beam particle:

      -NCASE (in COMMON CASLIM, with a minus sign to identify
             Sodraw output): number of primaries followed so far
      NPFLKA (in COMMON FLKSTK): stack pointer
      NSTMAX (in COMMON FLKSTK): highest value of the stack pointer
             encountered so far
      TKESUM (in COMMON SOURCM): total kinetic energy of the
             primaries of a user written source (see source.f
             here below), if applicable. Otherwise = 0.0
      WEIPRI (in COMMON SUMCOU): total weight of the primaries
             handled so far
      Npflka times: ILOFLK           : type of source particle
                    TKEFLK+AM        : total particle energy (kinetic+mass)
                    WTFLK            : source particle weight
                    XFLK, YFLK, ZFLK : source particle position
                    TXFLK, TYFLK, TZFLK : source particle direction cosines

  • USDRAW

Argument list (all variables are input only):

          ICODE : 10x: call from Kaskad (hadron and muon interactions)
                     100: elastic interaction secondaries
                     101: inelastic interaction secondaries
                     102: particle decay secondaries
                     103: delta ray generation secondaries
                     104: pair production secondaries
                     105: bremsstrahlung secondaries
                     110: radioactive decay products
                  20x: call from Emfsco (electron, positron and photon
                       interactions)
                     208: bremsstrahlung secondaries
                     210: Moller secondaries
                     212: Bhabha secondaries
                     214: in-flight annihilation secondaries
                     215: annihilation at rest secondaries
                     217: pair production secondaries
                     219: Compton scattering secondaries
                     221: photoelectric secondaries
                     225: Rayleigh scattering secondaries
                  30x: call from Kasneu (low-energy neutron interactions)
                     300: interaction secondaries
                  40x: call from Kashea (heavy ion interactions)
                     400: delta ray generation secondaries
          MREG             :  current region
          XSCO, YSCO, ZSCO : interaction point

USDRAW is called after each particle interaction (if requested by the user with USERDUMP, WHAT(4) >= 1.0). There is no default output: any output must be supplied by the user.

Information about the secondary particles produced is available in COMMON GENSTK, except that concerning delta rays produced by heavy ions (in which case the properties of the single electron produced are available in COMMON EMFSTK, with index NP). Another exception is that about heavy evaporation fragments (deuterons, 3-H, 3-He, alphas, with JTRACK ID equal respectively to -3, -4, -5, -6) and fission/fragmentation products generated in an inelastic interaction (with JTRACK = -7 to -12) which are all stored in COMMON FHEAVY, with index NPHEAV. To get the kinetic energy of particles with JTRACK < -6, one must subtract from their total energy (ETRACK} in COMMON TRACKR) their fully stripped nuclear mass (AMNHEA in COMMON FHEAVY).

Information about the interacting particle and its trajectory can be found in COMMON TRACKR (see description under the MGDRAW entry above). In TRACKR there are also some spare variables at the user's disposal: LLOUSE (integer), ISPUSR (integer array) and SPAUSR (double precision array). Like many other TRACKR variables, each of them has a correspondent in the particle stacks, i.e. the COMMONs from which the particles are unloaded at the beginning of their transport: FLKSTK, EMFSTK and OPPHST (respectively, the stack of hadrons/muons, electrons/photons, and optical photons). The correspondence with TRACKR is shown below under STUPRF/STUPRE. When a particle is generated, its properties (weight, momentum, energy, coordinates etc., as well as the values of the user flags) are loaded into one of the stacks. The user can write a STUPRF or STUPRE subroutine (see description below) to change anyone of such flags just before it is saved in stack. When a particle starts to be transported, its stack variables are copied to the corresponding TRACKR ones. Unlike the other TRACKR variables, which in general become modified during transport due to energy loss, scattering etc., the user flags keep their original value copied from stack until they are changed by the user himself (generally in USDRAW). One common application is the following: after an interaction which has produced sencondaries, let USDRAW copy some properties of the interacting particle into the TRACKR user variables. When STUPRF is called next to load the secondaries into stack, by default it copies the TRACKR user variables to the stack ones. In this way, information about the parent can be still carried by its daughters (and possibly by further descendants). This technique is sometimes referred to as "latching".


13.2.14 ophbdx.f user defined Optical PHoton BounDary-(X)crossing properties

Argument list (all variables are input only):

          OMGPHO : angular frequency (omega = 2 pi nu) of the photon (in s-1)
          WVLNGT : photon wavelength (in cm)
          MREG   : old region number
          NEWREG : new region number
          SIGANW : absorption coefficient in the new region (cm-1)
          SIGDNW : diffusion  coefficient in the new region (cm-1)
          RFNDPR : refractive index in the new region
          VGRPNW : group velocity in the new region (cm s-1)
          LPHKLL : if .TRUE., the photon will be absorbed on the boundary

Subroutine OPHBDX sets the optical properties of a boundary surface. The call is activated by command OPT-PROP, with SDUM = SPEC-BDX. See option OPT-PROP and Chap. (12) for more information.


13.2.15 queffc.f: user defined QUantum EFFiCiency

Argument list (all variables are input only):

          WVLNGT : photon wavelength (in cm)
          OMGPHO : angular frequency (omega = 2pi nu) of the photon (in s-1)

Function QUEFFC returns a user-defined quantum efficiency for an optical photon of the given wavelength or frequency. It is activated by OPT-PROP, with SDUM = SENSITIV, by setting the 0th photon sensitivity parameter to a value < -99. See option OPT-PROP and Chap. (12) for more information.


13.2.16 rflctv.f: user defined ReFLeCTiVity

Argument list (all variables are input only):

          WVLNGT : photon wavelength (in cm)
          OMGPHO : angular frequency (omega = 2pi nu) of the photon (in s-1)
          MMAT   : material index

Function RFLCTV returns a user-defined value equal to 1-R, where R is the reflectivity of the current material for an optical photon of the given wavelength or frequency. It is activated by OPT-PROP, with SDUM = METAL, and WHAT(3) < -99. See option OPT-PROP and Chap. (12) for more information.


13.2.17 rfrndx.f: user defined ReFRaction iNDeX

Argument list (all variables are input only):

          WVLNGT : photon wavelength (in cm)
          OMGPHO : angular frequency (omega = 2pi nu) of the photon (in s-1)
          MMAT   : material index

Function RFRNDX returns a user-defined refraction index of the current material for an optical photon of the given wavelength or frequency. It is activated by OPT-PROP, with SDUM = blank, and WHAT(1) < -99. See option OPT-PROP and Chap. (12) for more information.


13.2.18 soevsv.f SOurce EVent SaVing

No arguments

Subroutine SOEVSV is always called after a beam particle is loaded into FLKSTK, but a call to SOEVSV can be inserted by the user anywhere in a user routine. SOEVSV copies the whole FLKSTK to another COMMON, SOUEVT, which can be included in other user routines. In other words, this routine is used to "take a snapshot" of the particle bank at a particular time for further use (interfacing to independent generators, etc.)


13.2.19 source.f user-written source

Argument list:

          NOMORE : if set = 1, no more calls will occur (the run will be
                   terminated after exhausting the primary particles loaded
                   into FLKSTK stack in the present call). The history number
                   limit set with option START will be overridden.

Subroutine SOURCE is probably the most frequently used user routine. It is activated by option SOURCE and is used to sample primary particle properties from distributions (in space, energy, time, direction, polarisation or mixture of particles) too complicated to be described with the BEAM, BEAMPOS and POLARIZAti cards alone. For each phase-space variable, a value must be loaded into COMMON FLKSTK (particle bank) before returning control. These values can be read from a file, generated by some sampling algorithm, or just assigned.

  • Reading from a file

Reading from a file is needed, for instance, when the particle data are taken from a collision file, written by FLUKA or by another program. The user must open the file with a unit number > 20 (unit numbers lower than 20 are reserved), in one of the following ways:

  • Using option OPEN, with SDUM = OLD
  • In a user subroutine USRINI or USRGLO (see below), with a Fortran OPEN statement. Option USRICALL (resp. USRGCALL) is needed to activate the call to the routine.
  • With an OPEN statement in the initialisation part of subroutine SOURCE itself.

Then, a READ statement in SOURCE can be used to get the data to load in stack, for instance:

            READ(21,*) IPART, X, Y, Z, COSX, COSY, COSZ, ENERGY, WEIGHT
            ILOFLK (NPFLKA) = IPART
            XFLK   (NPFLKA) = X
            YFLK   (NPFLKA) = Y
            ZFLK   (NPFLKA) = Z
            TXFLK  (NPFLKA) = COSX
            ...etc...
          (NPFLKA is the current stack index).

  • Direct assignment

Direct assignment can be done explicitly, for instance:

            PMOFLK (NPFLKA) = 305.2D0

or implicitly, leaving unmodified values input with BEAM or BEAMPOS:

            PMOFLK (NPFLKA) = PBEAM

(PBEAM is the momentum value input as WHAT(1) in option BEAM). A set of direct assignments, one for each of several different stack entries, can be useful, for example, to define a series of RAYs through the geometry (see (14)):

          DO 10 I = 1, 20
             NPFLKA = NPFLKA + 1
             ILOFLK (NPFLKA) = 0                 (0 is the RAY particle id number)
             XFLK  (NPFLKA) = 500.D0 + DBLE(I) * 40.D0
             YFLK  (NPFLKA) = 200.D0
             ...etc...
      10  CONTINUE

  • Sampling from a uniform distribution

To sample from a uniform distribution, the user must use the function FLRNDM(DUMMY), which returns a double precision pseudo-random number uniformly distributed between 0 (included) and 1 (not included). Actually, DUMMY can be any variable name. A simple example of sampling from a uniform distribution is that of a linear source along the Z axis, between Z = 10 and Z = 80:

          Z1 = 10.D0
          Z2 = 80.D0
          ZFLK (NPFLKA) = 10.D0 + (Z2 - Z1) * FLRNDM(XXX)

  • Sampling from a generic distribution

One way to sample a value XX from a generic distribution f(x) is the following. First integrate the distribution function, analytically or numerically, and normalise to 1 to obtain the normalised cumulative distribution:

                             /x            /xmax
                     F(x) =  |  f(x)dx  /  |  f(x)dx
                             /xmin         /xmin

Then, sample a uniform pseudo-random number t using FLRNDM and get the desired result by finding the inverse value:

                          -1
                    XX = F (t)

(analytically or most often by interpolation).

A FLUKA subroutine is available to sample directly from a Gaussian distribution:

             CALL FLNRRN (RGAUSS)

or, if two independent Gaussian distributed numbers are needed:

             CALL FLNRR2 (RGAUS1, RGAUS2)

(faster than calling FLNRRN twice).

  • Sampling from a biased distribution

The technique for sampling from a generic distribution described above can be extended to modify the probability of sampling in different parts of the interval (importance sampling). We replace f(x) by a weighted function g(x) = f(x) * h(x), where h(x) is any appropriate function of x we like to choose. We normalise g(x) in the same way as f(x) before:

                  /x            /xmax       /x
          G(x) =  |  g(x)dx  /  |  g(x)dx = |  f(x)*h(x)dx / B
                  /xmin         /xmin       /xmin

and we need also the integral of f(x) over the whole interval:

                  /xmax
              A = |  f(x)dx
                  /xmin

All the sampling is done using the biased cumulative normalised function G instead of the original unbiased F: we sample a uniform pseudo-random number t as before, and we get the sampled value XX by inverting G(x):

                    -1
              XX = G (t)

The particle is assigned a weight B/(A * h(XX))

A special case of importance sampling is when the biasing function chosen is the inverse of the unbiased distribution function:

              h(x) = 1/f(x)
              g(x) = f(x) * h(x) = 1
              G(x) = (x - xmin) / (xmax - xmin)

In this case we sample a uniform pseudo-random number t using FLRNDM as shown above. The sampled value XX is simply given by:

                        XX = xmin + (xmax - xmin)*t

and the particle is assigned a weight:

                                                     /xmax
                B/(A h(X)) = f(XX)*(xmax - xmin)  /  |  f(x)dx
                                                     /xmin

But since FLUKA normalizes all results per unit primary weight, any constant factor is eliminated in the normalization. Therefore it is sufficient to assign each particle a weight f(x).

Because XX is sampled with the same probability over all possible values of x, independently of the value f(XX) of the function, this technique is used to ensure that sampling is done uniformly over the whole interval, even though f(x) might have very small values somewhere. For instance it may be important to avoid undersampling in the high-energy tail of a spectrum, steeply falling with energy but more penetrating, such as that of cosmic rays or synchrotron radiation.

Option SOURCE allows the user to input up to 12 numerical values (WHASOU(1),(2)...(12)) and one 8-character string (SDUSOU) which can be accessed by the subroutine by including the following line:

                INCLUDE '(SOURCM)'

These values can be used as parameters or switches for a multi-source routine capable to handle several cases, or to identify an external file to be read, etc., without having to compile and link again the routine.

In the SOURCE routine there are a number of mandatory statements, (clearly marked as such in accompanying comments) which must not be removed or modified. The following IF block initialises the total kinetic energy of the primary particles and sets two flags: the first to skip the IF block in all next calls, and the second to remind the program, when writing the final output, that a user source has been used:

    *  +-------------------------------------------------------------------*
    *  |  First call initialisations:
          IF ( LFIRST ) THEN
    *  |  *** The following 3 cards are mandatory ***
             TKESUM = ZERZER
             LFIRST = .FALSE.
             LUSSRC = .TRUE.
    *  |  *** User initialisation ***
          END IF
    *  |
    *  +-------------------------------------------------------------------*

The user can insert into the above IF block any other initialisation needed, for instance the preparation of a cumulative spectrum array from which to sample the energy of the source particles. Note that user initialisation can take place also in routines USRINI and USRGLO (activated at input time by input options USRICALL and USRGCALL) and USREIN (called before unloading from stack the first source particle of an event, i.e., just after the call to SOURCE)

At the time SOURCE is called, the particle bank FLKSTK is always empty and the stack pointer NPFLKA has value 0. The user can load into the FLKSTK stack one or more source particles at each call: for each particle loaded the pointer must be increased by 1. The template version of SOURCE loads only one particle: if several are loaded the following sequence, until the statement CALL SOEVSV not included, must be repeated once for each particle, possibly inside a DO loop:

           NPFLKA = NPFLKA + 1             increases the pointer

The following statements assign a value to each of the FLKSTK variables concerning the particle being loaded:

           WTFLK (NPFLKA) = ONEONE           sets the weight of the particle = 1.
              This must be changed if the sampling of one or more of the
              particle properties are biased. In that case, generally the weight
              must be set after the sampling, and its value depends on the
              sampling outcome.

           WEIPRI = WEIPRI + WTFLK (NPFLKA)  updates the total weight of the
              primaries (don't change)

           ILOFLK (NPFLKA) = IJBEAM          by default sets the type of particle
              equal to the one defined by the BEAM card. If no BEAM card is
              given in input, IJBEAM is = 1 (proton), but it is strongly
              recommended to always provide a BEAM command in input (see Note 1
              at the end of Section 13.2.19}).

The above statement is followed by several others that must not be changed or removed. In the template routine, they are encompassed by the comment lines:

             From this point .... / ... to this point: don't change anything

These statements are:

    * From this point ....
          LOFLK (NPFLKA) = 1                Generation is 1 for source particles
          LOUSE (NPFLKA) = 0                User variables: the user can set
          DO 100 ISPR = 1, MKBMX1           different values in the STUPRF or
             SPAREK (1,NPFLKA) = ZERZER     STUPRE routine, but it is better
     100  CONTINUE                          not to do it here
          DO 200 ISPR = 1, MKBMX2
             ISPARK (ISPR,NPFLKA) = 0       More user variables (integer)
     200  CONTINUE
          NPARMA = NPARMA + 1               Updating the maximum particle number
          NUMPAR (NPFLKA) = NPARMA          Setting the current particle number
          NEVENT (NPFLKA) = 0               Resetting the current event number
          DFNEAR (NPFLKA) = +ZERZER         Resetting the distance to the
                                            nearest boundary
    * ... to this point: don't change anything

The following statements can be overridden or rewritten by the user, assigning new values or sampling them from problem-dependent distributions. First three statements which are rarely modified:

          AGESTK (NPFLKA) = +ZERZER         Particle age is zero by default
          AKNSHR (NPFLKA) = -TWOTWO         Resets the Kshort component of
                                            K0/K0bar. Usually not to be changed.
          IGROUP (NPFLKA) = 0               Group number for low energy
                                            neutrons: if set to 0, the program
                                            derives it from the kinetic energy

Then the most frequently changed lines: both energy and momentum of the particle must be loaded onto FLKSTK, but the two cannot be defined independently. Appropriate kinematical (relativistic) relations must be applied to derive one from the other.

In the template routine, the momentum is assumed to be assigned by BEAM option (its value, PBEAM, is taken from COMMON BEAMCM, which contains all values defined by options BEAM and BEAMPOS).

          PMOFLK (NPFLKA) = PBEAM
          Therefore, the kinetic energy (in GeV) must be derived:

          TKEFLK (NPFLKA) = SQRT ( PBEAM**2 + AM (IJBEAM)**2 ) - AM (IJBEAM)

          (where AM is the rest mass, in COMMON PAPROP, and  IJBEAM is the
          particle type, in COMMON BEAMCM)

If instead the energy had been sampled first from some spectrum, and ENSAMP would be the sampled value, the two statements above would become:

          TKEFLK (NPFLKA) = ENSAMP
          PMOFLK (NPFLKA) = SQRT(ENSAMP * (ENSAMP + TWOTWO * AM(IJBEAM)))

The direction cosines are loaded next:

          TXFLK (NPFLKA) = UBEAM              Assumed here to be the same as
          TYFLK (NPFLKA) = VBEAM              defined by option BEAMPOS. UBEAM,
          TZFLK (NPFLKA) = WBEAM              VBEAM, WBEAM are some among the beam
                                           properties in COMMON BEAMCM.
          (If BEAMPOS is not given, by default UBEAM = VBEAM = 0.0, WBEAM= 1.0)

Remember to make sure that the cosines are normalised! One could replace the last statement by:

          TZFLK (NPFLKA) = SQRT ( ONEONE - TXFLK(NPFLKA)**2 - TYFLK(NPFLKA)**2 )

The polarisation cosines are not set by default:

          TXPOL (NPFLKA) = -TWOTWO          -2 is a flag for "no polarisation"
          TYPOL (NPFLKA) = +ZERZER
          TZPOL (NPFLKA) = +ZERZER

but appropriate values need to be given in some cases, for instance in synchrotron radiation shielding problems.

Finally the particle coordinates, set again by default equal to those input with BEAMPOS:

          XFLK (NPFLKA) = XBEAM               Assumed here to be the same as
          YFLK (NPFLKA) = YBEAM               defined by option BEAMPOS. XBEAM,
          ZFLK (NPFLKA) = ZBEAM               YBEAM, ZBEAM are also in COMMON
                                              BEAMCM.
          (If BEAMPOS is not given, by default XBEAM = YBEAM = ZBEAM = 0.0)

If for example our problem required instead a linear source uniformly distributed along Z between Z1 and Z2, we could replace the last statement by:

          ZFLK (NPFLKA) = Z1 + FLRNDM(UGH) * (Z2 - Z1)

The following lines in the template SOURCE routine should never be changed. They calculate the total energy of the primary particles, define the remaining properties of the particles (starting region and lattice cell) and do some geometry initialisation. The last line calls the SOEVSV user routine (see description above) to save the stack for possible further use.


IMPORTANT!

Note 1: Even though a user-written source is used, it is recommended to issue in input a card BEAM with an energy larger than the maximum energy that can be sampled by the user source. This value is used to set up tables such as stopping powers, cross sections etc., and if not provided, crashes can occur. Note 2: The values of beam characteristics defined by commands BEAM and POLARIZAti are available in COMMON BEAMCM: the angular divergence (variable DIVBM), beam width (XSPOT and YSPOT), and the polarisation vector (UBMPOL, VBMPOL, WBMPOL) can help to set up a scheme to sample the corresponding quantities from user-defined distributions. But sampling from the distributions pre-defined by BEAM and POLARIZAti is not simply inherited by subroutine SOURCE: it is the responsibility of the user to write such a scheme! For this task, it may be useful to define a "beam reference frame" by means of option BEAMAXES (see more details at the BEAMAXES command).


13.2.20 stupre.f SeT User PRoperties for EMF particles stuprf.f SeT User PRoperties for FLUKA particles

MF particles stuprf.f SeT User PRoperties for FLUKA particles|stupre.f SeT User PRoperties for EMF particles stuprf.f SeT User PRoperties for FLUKA particles|99|13| -->

These two functions are used to assign a value to one or more stack user variables when the corresponding particle is loaded into one of the stacks (FLKSTK for hadrons/muons, EMFSTK for electrons/photons, OPPHST for optical photons). In each of these stacks the user has access to one integer variable, one integer array and one double precision array. Each of them is copied to a correspondent variable or array in COMMON TRACKR at the beginning of transport:

          Correspondence:               FLKSTK  EMFSTK   OPPHST       TRACKR
          --------------                -----   ------   ------       ------
             integer variable:          LOUSE   LOUEMF   LOUOPP  -->  LLOUSE
             integer array:             ISPARK  IESPAK   ISPORK  -->  ISPUSR
             double precision array:    SPAREK  ESPARK   SPAROK  -->  SPAUSR

The user can access and modify the TRACKR variables via subroutine MGDRAW and its entries ENDRAW, SODRAW and especially USDRAW (see description above). STUPRF and STUPRE can be used to do the reverse, namely to copy TRACKR user variables to those of the relevant stack (see USDRAW above).

  • STUPRE is called before loading into stack electrons, positrons and photons.

No arguments

The default version does nothing (the user variables of the parent particle are already set equal to the original projectile by the various electromagnetic interaction routines. Also the region/position etc. are already set inside the stack arrays.

  • STUPRF is called before loading into stack hadrons, muons, neutrinos,
    low-energy neutrons, heavy ions and optical photons

Argument list:

          IJ         : type of the parent particle
          MREG       : current region
          XX, YY, ZZ : particle position
          NUMSEC     : index in the GENSTK COMMON of the secondary being loaded
                       onto stack
          NPPRMR     : if > 0, the secondary being loaded is actually still the
                       interacting particle (it can happen in some biasing
                       situations)

Note that heavy ions in FLUKA carry all the same id-number IJ = -2. The characteristics of primary ions are characterised by option HI-PROPE. To obtain the those of a secondary ion, call the routine USRDCI 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

The default version of STUPRF copies to stack the user flags of the parent.


13.2.21 ubsset.f User BiaSing SETting

Argument list:

          IR     : region number
          RRHADR : multiplicity biasing factor to be applied to the
                   secondaries from hadronic interactions in region IR
                   (WHAT(2) of card BIASING)
          HMPHAD : Importance of region IR for hadrons and muons (WHAT(3) of
                   card BIASING, with WHAT(1) = 0 or 1).
                   Actually the routine argument is an integer, IMPHAD, equal
                   to importance multiplied by 10000, but the user should
                   consider only the double precision version HMPHAD
                   (a conversion from and to the integer version is provided
                   at the beginning and at the end of the routine, and should
                   not be changed).
          HMPLOW : Importance of region IR for low energy neutrons (WHAT(3)
                   of card BIASING, with WHAT(1) = 0 or 3).
                   Actually the routine argument is an integer, IMPLOW, equal
                   to importance multiplied by 10000, but the user should
                   consider only the double precision version HMPLOW
                   (a conversion from and to the integer version is provided
                   at the beginning and at the end of the routine, and should
                   not be changed).
          HMPEMF : Importance of region IR for electrons and photons (WHAT(3)
                   of card BIASING, with WHAT(1) = 0 or 2).
                   Actually the routine argument is an integer, IMPEMF, equal
                   to importance multiplied by 10000, but the user should
                   consider only the double precision version HMPEMF
                   (a conversion from and to the integer version is provided
                   at the beginning and at the end of the routine, and should
                   not be changed).
          IGCUTO : Cutoff group index for low energy neutrons in region IR
                   (WHAT(1) in card LOW-BIAS)
          IGNONA : Non-analogue absorption group limit for low energy neutrons
                   in region IR (WHAT(2) in card LOW-BIAS)
          PNONAN : Non-analogue survival probability for low energy neutrons in
                   region IR (WHAT(3) in card LOW-BIAS)
          IGDWSC : Group limit for biased downscattering for low energy
                   neutrons in region IR (WHAT(1) in card LOW-DOWN)
          FDOWSC : Biased downscattering factor for low energy neutrons in
                   region IR (WHAT(2) in card LOW-DOWN)
          JWSHPP : Weight-Window/importance profile index for low energy
                   neutrons in region IR (SDUM in WW-FACTO)
          WWLOW  : Weight-Window lower level in region IR (WHAT(1) in card
                   WW-FACTO, possibly modified by WHAT(4) in WW-THRES or
                   WHAT(2) in WW-PROFI)
          WWHIG  : Weight-Window upper level in region IR (WHAT(2) in card
                   WW-FACTO, possibly modified by WHAT(4) in WW-THRES or
                   WHAT(2) in WW-PROFI)
          WWMUL  : Weight-Window multiplicative factor applied to the two
                   energy thresholds defined with WW-THRES, for region IR
                   (WHAT(3) in card WW-FACTO)
          EXPTR  : Exponential transform parameter for region IR (WHAT(2) in
                   card EXPTRANS) (not implemented yet!!!!!!!!)
          ELECUT : e+,e- cutoff in region IR (WHAT(1) in card EMFCUT)
          GAMCUT : Photon cutoff in region IR (WHAT(2) in card EMFCUT)
          LPEMF  : Leading Particle Biasing flag in region IR (SDUM = LPBEMF
                   in card EMF-BIAS, or WHAT(3) in card EMFCUT)
          ELPEMF : Maximum e+/e- energy for applying Leading Particle Biasing
                   (WHAT(2) in card EMF-BIAS with SDUM = LPBEMF)
          PLPEMF : Maximum photon energy for applying leading particle
                   biasing (WHAT(3) in card EMF-BIAS with SDUM = LPBEMF)

Subroutine UBSSET does not require a special command to be activated: it is always called several times for each region: (once for every biasing option or suboption) after the end of input reading and before starting the calculations. The default version is a dummy and does nothing. The user can replace it to override any biasing parameters specified in input.

The UBSSET subroutine is used especially in cases with a large number of regions, because it allows to derive the biasing parameters from simple algorithms instead of entering each input value by hand. Choosing an appropriate numbering scheme for the geometry regions can often facilitate the task. For instance, assuming a simple slab geometry with an expected exponential hadron attenuation from region 3 to region 20, each region being one half-value-layer thick, one could write the following in order to set importances that would keep the hadron number about constant in all regions:

          IF(IR .GE. 3 .AND. IR .LE. 20) HMPHAD = ONEONE * TWOTWO**(IR-3)

It is important, however, not to do recursive assignments of the type:

          GAMCUT(5) = GAMCUT(5) * HLFHLF  (HLFHLF is a FLUKA constant for 0.5D0)

because that would halve the value of the photon cutoff for Region 5 AT EVERY CALL, and the number of calls is not known to the user.


13.2.22 udcdrl.f User defined DeCay DiRection biasing and Lambda


(for neutrinos only)

Argument list:

          IJ     : type of decaying particle
          KPB    : outgoing neutrino, the one direction biasing is asked for
          NDCY   : (???)
          UDCDRB, VDCDRB, WDCDRB : cosines of the preferential outgoing
                                   direction for the neutrino

Function UDCDRL is used to bias the direction of a neutrino emitted by a decaying particle of type IJ. The value returned by UDCDRL is the Lambda for direction biasing (1-cos(theta)) (???)


13.2.23 usimbs.f User defined IMportance BiaSing

Argument list:

          input:
            MREG   : region at the beginning of the step
            NEWREG : region at the end of the step
          output:
            FIMP   : returns the user-defined importance ratio between the
                     position at the end and at the beginning of the step

The routine is called AT EVERY PARTICLE STEP. It can be used to implement any importance biasing scheme based on region number and on phase space coordinates and other information provided by COMMON TRACKR.

WARNING: The user must balance the very effective biasing power offered by the routine with the important demand on CPU time due to the large number of calls.


13.2.24 usrein.f USeR Event INitialisation

No arguments

Subroutine USREIN is called just before the first source particle of an event is unloaded from stack and begins to be transported. An event is the full history of a group of related particles and their descendants. If primaries are loaded into stack by the input option BEAM, there is only one source particle per event; but there can be more if the user routine SOURCE is used to load particles into stack. USREIN does not need any special command to be activated, but the default version of USREIN does nothing: the user can write here any kind of initialisation.


13.2.25 usreou.f USeR Event OUtput (called at the end of each event)

No arguments

Subroutine USREOU is called at the end of each event, namely after all event primary particles and their descendants have been transported. (See USREIN above for a definition of an event). USREOU does not need any special command to be activated, but the default version of USREOU does nothing: the user can write here any kind of event analysis, output, etc.


13.2.26 usrglo.f USeR GLObal settings

Argument list:

          WHAT(1), (2), (3), (4), (5), (6) : user-given numerical parameters
          SDUM : user-given character string (8 characters)

Subroutine USRGLO is called before any other initialisation is done by the program, provided a command USRGCALL is present anywhere in the input. The calling parameters can carry any kind of useful information or can be used as flags to choose between different possible actions to be performed before any particle transport takes place.


13.2.27 usrini.f USeR INItialisation

Argument list:

          WHAT(1), (2), (3), (4), (5), (6) : user-given numerical parameters
          SDUM : user-given character string (8 characters)

Subroutine USRINI is called every time a USRICALL card is read in input. It can be used to do any kind of initialisation: reading and manipulating data from one or more files, calling other private routines, etc. The calling parameters can carry any kind of useful information or can be used as flags to choose between different possible actions to be performed before any particle transport takes place.


13.2.28 usrmed.f USeR MEDium dependent directives

Argument list:

          IJ            : particle type
          EKSCO         : particle kinetic energy (GeV)
          PLA           : particle momentum (GeV/c)
          WEE           : particle weight
          MREG          : previous region number
          NEWREG        : current region number
          XX, YY, ZZ    : particle position
          TXX, TYY, TZZ : particle direction

Subroutine USRMED is activated by option MAT-PROP with SDUM = USERDIRE, for one or more materials indicated by the user. It is called every time a particle is going to be transported in one of the user-flagged materials. Two cases are possible:

  • 1) MREG = NEWREG: the particle is going to move from a point inside the medium. The user is allowed to change only the particle weight. Typical application: simulating attenuation of optical photons in an absorbing medium by reducing the photon weight.
  • 2) MREG not = NEWREG: the particle is going to move from a point on a boundary between two different regions. The user may change any of the following: particle weight, current region number, direction cosines. Typical applications:
  • simulating refraction, by changing the direction cosines so that the particle is still inside the same region. To do this, one generally needs the direction cosines of the normal to the surface: TXNOR(NPFLKA), TYNOR(NPFLKA), TZNOR(NPFLKA) (COMMON FLKSTK must be included).
  • simulating reflection (albedo) at a boundary. The direction cosines must be modified according to some reflection law or albedo angular distribution, and NEWREG must be set = MREG.

In both cases the weight can also be reduced to account for surface reflectivity or similar (if the particle is an optical photon, the FRGHNS user function can be called to establish a surface roughness)


13.2.29 usrout.f USeR OUTput

Argument list:

          WHAT(1), (2), (3), (4), (5), (6) : user-given numerical parameters
          SDUM : user-given character string (8 characters)

Subroutine USROUT is called every time a USROCALL card is read in input. It is used to print special user-written output in addition to the standard one provided by default. The calling parameters can carry any kind of useful information or can be used as flags to choose between different possible actions to be performed after all particle transport has taken place.


13.2.30 usrrnc.f USeR Residual NuClei

Argument list:

          IZ            : atomic number of the residual nucleus
          IA            : mass number of the residual nucleus
          IS            : isomeric state of the residual nucleus
          X, Y, Z       : particle position
          MREG          : number of the current region
          WEE           : particle weight
          ICALL         : internal code calling flag (not for general use)

Subroutine USRRNC is called every time a residual nucleus is produced, if option USERWEIG has been requested with WHAT(5) > 0.

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