How to Declare a Spherical Neutron Source for Thermal Neutron Flux Calculation?

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SUMMARY

This discussion focuses on the declaration of a spherical neutron source for thermal neutron flux calculations using the MCNP (Monte Carlo N-Particle Transport Code) simulation software. Key parameters include the definition of the source location, the importance sampling line, and the energy definition for thermal neutrons. The correct configuration for the input file is emphasized, particularly ensuring the source is not positioned on the edge of two cells and addressing formatting issues in the input file. Participants suggest using a surface source as an alternative to simplify the setup.

PREREQUISITES
  • Understanding of MCNP input file structure and syntax
  • Knowledge of neutron transport theory and thermal neutron sources
  • Familiarity with importance sampling techniques in MCNP
  • Basic skills in file management and formatting for simulation inputs
NEXT STEPS
  • Research MCNP source definitions and configurations
  • Learn about importance sampling in MCNP simulations
  • Explore techniques for defining complex geometries in MCNP
  • Review best practices for formatting MCNP input files
USEFUL FOR

Researchers, nuclear engineers, and physicists involved in neutron transport simulations, particularly those working with thermal neutron flux calculations in MCNP.

Addali sabah
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TL;DR
how I can declare a spherical neutron source to calculate the thermal neutron flux in a cell
c Created on: Tuesday, September 05, 2023 at 11:26
1 1 -1.58 -1
2 0 -2 #1
3 0 -3 #1 #2
4 0 3

1 rpp -0.5 0.5 -0.5 0.5 0 0.1
2 so 10
3 so 15

mode n
m1 15000. 0.12951 $matrix
6000. 0.01731 12000. 0.00546 11000. 0.008
20000. 0.35857 13000. 0.002184 8000. 0.40146
16000. 0.0118 26000. 0.0026 14000. 0.0101
imp:n 1 1r 0 1 $ 1, 4
sdef cell=2 rad=d1 erg= 0.025 par=1
si1 0 10
f4:n 1
e4 1.01e-10 121i 0.025
nps 10000
 
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A few things to think about,

The void cell is 4, so your imp line should be 1 1 1 0 not 1 1 0 1, right?

You have a point source at 0 0 0 (default source location) is this on the edge of two cells? It needs to not be on the edge. If you want to make cell 2 a homogeneous source, a sphere with a box cut out of it, that is tricky. A surface source might be easier from surface 2, but it depends a lot on what the problem is.

erg= has a space before 0.025

If you rename your input file to add .txt you can attach it to a post, or you can paste into BB code tags, then we can see the version with the correct formatting.
 
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Likes   Reactions: Greg Bernhardt and berkeman
Thank you sir for your comments
Cell 1 is immersed in a thermal neutron source which is the cell 2
 

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