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USRBDX

defines a detector for a boundary crossing fluence or current estimator

See also USRBIN, USRCOLL, USRTRACK, USRYIELD

The full definition of the detector may require two successive cards (the second card, identified by the character '&' in any column from 71 to 78, must be given unless the corresponding defaults are acceptable to the user)

First card:

     WHAT(1) = i1 + i2 * 10 + i3 * 100, where i1, i2 i3 have the following
               meaning:
        i1  =  1.0 : linear binning in energy and solid angle
            = -1.0 : logarithmic binning in energy, linear in solid angle
            =  2.0 : logarithmic binning in solid angle, linear in energy
            = -2.0 : logarithmic binning in energy and solid angle
        i2  =  0.0 : one way scoring
            = +1.0 : two-way scoring
        i3  =  0.0 : current scoring
            = +1.0 : fluence scoring (inverse cosine-weighted)
            Default = 1.0 (one-way current, linear in energy and solid
                           angle)

     WHAT(2) = (generalised) particle type to be scored
             Default = 201.0 (all particles)

     WHAT(3) = logical output unit
             > 0.0 : formatted data are written on WHAT(3) unit
             < 0.0 : unformatted data are written on |WHAT(3)| unit
             Values of |WHAT(1)| < 21 should be avoided (with the
             exception of +11).
             Default = 11.0 (standard output unit)

     WHAT(4) = first region defining the boundary
               (in case of one-way scoring this is the upstream region)
               Default = 1.0

     WHAT(5) = second region defining the boundary
               (in case of one-way scoring this is the downstream region)
               Default = 2.0

     WHAT(6) = area of the detector in cm**2
               Default = 1.0

     SDUM    = any character string (not containing '&') identifying the
               detector (max. 10 characters)

Continuation card:

     WHAT(1) = maximum kinetic energy for scoring (GeV)
               Default: Beam particle total energy as set by the BEAM
               option (if no BEAM card is given, the energy corresponding
               to 200 GeV/c momentum will be used)

     WHAT(2) = minimum kinetic energy for scoring (GeV)
               Note that the lowest energy limit of the last neutron group
               is 1.E-14 GeV (1.E-5 eV) for the 260 data set.
               Default = 0.0 if linear energy binning, 0.001 GeV otherwise

     WHAT(3) = number of energy intervals for scoring
               Default = 10.0

     WHAT(4) = maximum solid angle for scoring in sr
               Default = 2 pi for one-way estimators, 4 pi for two-way

     WHAT(5) = If linear angular binning: minimum solid angle for
               scoring (sr)
               Default = 0.0
               If logarithmic angular binning: solid angle of the first
               bin (sr)
               Default = 0.001

     WHAT(6) = number of angular bins
               Default = 1.0 for linear angular binning, 3.0 otherwise

     SDUM    = & in any position in column 71 to 78

     Default (option USRBDX not given): no boundary crossing estimator detector

IMPORTANT!

Notes:

• 1) IMPORTANT! The results of a USRBDX boundary crossing estimator are always given as DOUBLE DIFFERENTIAL distributions of fluence (or current) in energy and solid angle, in units of cm-2 GeV-1 sr-1 per incident primary, EVEN WHEN ONLY 1 INTERVAL (BIN) HAS BEEN REQUESTED, which is often the case for angular distributions. Thus, for example, when requesting a fluence or current energy spectrum, with no angular distribution, to obtain INTEGRAL BINNED results (fluence or current in cm-2 PER ENERGY BIN per primary) one must multiply the value of each energy bin by the width of the bin (even for logarithmic binning), AND BY 2 pi or 4 pi (depending on whether one-way or two-way scoring has been requested). Angular distributions must be intended as distributions in cos(theta), where theta is the angle between the particle trajectory and the normal to the boundary at the point of crossing. When logarithmic scoring is requested for angular distributions, all intervals have all the same logarithmic width (equal ratio between upper and lower limit of the interval), EXCEPT THE FIRST ONE. The limits of the first angular interval are theta = 0 and the value indicated by the user with WHAT(5) in the second USRBDX card.

• 2) Angular distributions must be intended as distributions in cos(theta), where theta is the angle between the particle trajectory and the normal to the boundary at the point of crossing. When logarithmic scoring is requested for angular distributions, all intervals have the same logarithmic width (equal ratio between upper and lower limit of the interval), EXCEPT THE FIRST ONE. The limits of the first angular interval are theta=0 and the value indicated by the user with WHAT(5) in the second USRBDX card.

• 3) If the generalised particle is 208.0 (ENERGY) or 211.0 (EM-ENRGY), the quantity scored is differential energy fluence (if cosine-weighted) or differential energy current (energy crossing the surface). In both cases the quantity will be expressed in GeV per cm2 per energy unit per steradian per primary. That can sometimes lead to confusion since GeV cm-2 GeV-1 sr-1 = cm-2 sr-1, where energy does not appear. Note that integrating over energy and solid angle one gets GeV/cm2.

• 4) The maximum number of boundary crossing detectors that the user can define is 1100. This value can be changed by modifying the parameter MXUSBX in member USRBDX of the flukaadd library or directory and then re-compiling and linking FLUKA.

• 5) The logical output unit for the estimator results (WHAT(3) of the first USRBDX card) can be any one of the following:

• the standard output unit 11: estimator results will be written on the same file as the standard FLUKA output
• a pre-connected unit (via a symbolic link on most UNIX systems,
  ASSIGN under VMS, or equivalent commands on other systems)
  
• a file opened with the FLUKA command OPEN
• a file opened with a Fortran OPEN statement in a user-written initialisation routine such as USRINI, USRGLO or SOURCE (see (13))
  
• a dynamically opened file, with a default name assigned by the Fortran compiler (typically fort.xx or ftn.xx, with xx equal to the chosen logical output unit number).

The results of several USRBDX detectors in a same FLUKA run can be written on the same file, but of course only if they are all in the same mode (all formatted, or all unformatted). It is also possible in principle to write on the same file the results of different kinds of estimators (USRTRACK, USRBIN, etc.) but this is not recommended, especially in the case of an unformatted file, because it would make very difficult any reading and analysis.

• 6) When scoring neutron fluence or current, and the requested energy bin structure overlaps with that of the low energy neutron groups, bin boundaries are forced to coincide with group boundaries and no bin can be smaller than the corresponding group. Actually, the program uses the requested energy limits and number of bins to estimate the desired bin width. The number of bins above the upper limit of the first low-energy neutron group is recalculated according to such width. Note that the lowest energy limit of the last neutron group is 1.E-14 GeV (1.E-5 eV) for the 260 data set. All group energy boundaries are listed in two Tables in (10).

• 7) A program USXSUW is available with the normal FLUKA code distribution in directory $FLUPRO/flutil. USXSUW reads USRBDX results in binary form from several runs and allows to compute standard deviations. It returns double differential and cumulative fluence, with the corresponding percent errors, in a file, and in another file formatted for easy plotting. It also returns a binary file that can be read out in turn by USXSUW. The content of this file is statistically equivalent to that of the sum of the files used to obtain it, and it can replace them to be combined with further output files if desired (the USXSUW program takes care of giving it the appropriate weight).

Example:

 *...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
 USRBDX         101.0  ANEUTRON      21.0       3.0       4.0    400.0 AntiNeu
 USRBDX           5.0       0.0     200.0       0.0       0.0      0.0 &
 *  Calculate fluence spectrum from 0 to 5 GeV, in 200 linear energy intervals,
 *  of antineutrons passing from region 3 to region 4 (and not from 4 to 3).
 *  Write formatted results on unit 21. The area of the boundary is 400 cm2.
 *  A single angular interval is requested (from 0 to 2pi)