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McStas: Virtual_mcnp_input Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The Virtual_mcnp_input Component

This component uses a filename of recorded neutrons from the reactor monte carlo code MCNP as a source of particles.


  • Author: Chama Hennane and E. Farhi
  • Origin: ILL
  • Date: June 28th, 2006
  • Version:(Unknown)
  • Modification history:
    • EF, July 25th 2006: bug fixes.


This component generates neutron events from a filename created using the
MCNP Monte Carlo code for nuclear reactors. It is used to
calculate flux exiting from hot or cold neutron sources.
Neutron position and velocity is set from the filename. The neutron time is
left at zero.

Note that axes orientation may be different between MCNP and McStas.
The component has the ability to center and orient the neutron beam to the Z-axis.
It also may change the coordinate system from the MCNP frame to the McStas one.
The verbose mode is highly recommended as it displays lots of useful informations.
To obtain absolute intensity, set 'intensity' and 'nps' parameters.
The source total intensity is 1.054e18 for LLB/Saclay (14 MW) and 4.28e18 for
ILL/Grenoble (58 MW).

Format of MCNP events are :

  position_X position_Y position_Z dir_X dir_Y dir_Z Energy Weight Time

energy is in Mega eV, time in shakes (1e-8 s),
positions are in cm and the direction vector is normalized to 1.

We recommend NOT to use parallel execution (MPI) with this component. If you
need to, set parameter 'smooth=1'.

To generate PTRAC files using MCNP/MCNPX, add at the end of your input file:
  f1:n          2001              // tally
  ptrac         filename = asc
                max  = -1000000   // number of neutrons to generate and stop
                write = all
                event = sur
                filter = 2001,jsu // surface tally id
To create a 'source' from a MCNP simulation event file for the ILL:
COMPONENT source = Virtual_mcnp_input(
   filename = "H10p", intensity=4.28e18, nps=11328982,
   verbose = 1, autocenter="translate rotate rescale")

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
filename str Name of the MCNP PTRAC neutron input file. Empty string "" unactivates component 0
autocenter str String which may contain following keywords. "translate" or "center" to center the beam area AT (0,0,0) "rotate" or "orient" to center the beam velocity along Z "change axes" to change coordinate system definition "rescale" to adapt intensity to abs. units. with factor intensity/nps. Other words are ignored. 0
repeat_count 1 Number of times the source must be generated. 0 unactivates the component 1
verbose 0|1 Displays additional informations if set to 1 0
intensity n/s Intensity multiplication factor 0
MCNP_ANALYSE 1 Number of neutron events to read for file pre-analysis. Use 0 to analyze them all. 10000
surface_id 1 Index of the emitting MCNP surface to use. -1 for all. -1
nps 1 Number of total events shot by MCNP to generate the PTRAC as indicated at the end of the MCNP 'o' file as 'source particle weight for summary table normalization' or alternatively 'nps = '. 0
smooth 0/1 Smooth sparsed event files for file repetitions. 1


  • Source code for Virtual_mcnp_input.comp.
  • MCNP
  • MCNP -- A General Monte Carlo N-Particle Transport Code, Version 5, Volume II: User's Guide, p177

[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <> / Fri May 7 10:17:14 2021

Last Modified: Friday, 07-May-2021 12:17:14 CEST
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