MCNP: How to specify a small source in a large lattice

[enakker]

I am working on an input file in MCNPX/6 that uses a CT scan lattice geometry. I want to specify a small source in a large universe (lung). Right now I have a source uniformly distributed through the universe. The existing documentation is vague on this topic. Is it possible to contain the source in just a few of the voxels? Thanks for any suggestions or help!

Source definition:
SDEF PAR=D1 ERG=D2 CEL=D3 X=D4 Y=D5 Z=D6 $ Particle dist Energy dist
C
SI1 L 34 3 3 34
SP1 .42 .25 .16 .17
C
SI2 L 6.00 .7117 2.1318 7.69
SP2 .42 .25 .16 .17 $ Particle energy short-lived
C
SI3 L (4<6<8) $ 4 is the lung universe, 6 is the lattice unit cell, and 8 contains the lattice
SP3 1
C
SI4 H -25.048828 -24.658203
SP4 D 0 1
C
SI5 H -50.048828 -49.658203
SP5 D 0 1
C
SI6 H 21.625 21.875
SP6 D 0 1
C

 

[AndyW]

Hello,

Thank you for your question. It is possible to specify a small source in a large universe using the CT scan lattice geometry in MCNPX/6. Here are some suggestions to help you achieve this:

1. Use the SDEF card to define your source. This card allows you to specify the source location, energy, and distribution in the universe. In your case, you can use the CEL option to specify the voxels in which you want the source to be located. For example, if you want to contain the source in just a few voxels within the lung universe, you can use the CEL option to specify those voxels.

2. You can also use the SDEF card to define the energy distribution of your source. This will allow you to specify the energy of the particles in the voxels you have selected. You can use the ERG option to specify the energy distribution. For example, you can use a Gaussian distribution to specify the energy of the particles in the selected voxels.

3. Another option is to use the SDEF card to define the particle distribution in the selected voxels. This will allow you to specify the type of particles (e.g. neutrons, photons) in the selected voxels. You can use the PAR option to specify the particle distribution.

4. You can also use the SDEF card to define the location of the source within the selected voxels. This will allow you to specify the exact coordinates of the source within the voxels. You can use the X, Y, and Z options to specify the coordinates.

I hope these suggestions help. If you need more specific guidance, please refer to the MCNPX/6 documentation or contact the MCNPX/6 support team for further assistance.