Changing KMESH/KINTS from azimuthal to polar direction in MCNP6

In summary: I want to use cylindrical coordinates to model the source. I would like to use the FMESH tally in cylindrical coordinates. Is there a way to do this?In summary, you can use GEOM=CYL to get the dose from a cylindrical source in MCNP6. You need to find the conversion factors for each energy bin, and enter them into the tally.
  • #1
khary23
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6
I am modeling a cylindrical source in MCNP6 and would like to use the FMESH tally in cylindrical coordinates. I am looking for the dose to water from the source as a function of radial distance as well as polar angle running from 0 to 180 degrees in the YZ plane not around Z. Is there a way to do this?
 
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  • #2
Sure. I'm looking at the MCNP6 version 1 user manual and it's Section 3.3.5.25, page 3-67. You use GEOM=CYL then the I direction is radial, J is the z direction, and K is the theta.

To get the dose you need the conversion factors. These allow you to convert from a flux at a particular energy to a dose. You will find a table that gives the energy range split up into a bunch of bins, and dose conversion factor for each bin. You can get those from the appropriate health physics standard. You enter them in the same way you would with a type F4 tally. That's detailed in Section 3.3.5.8, page 3-211.
 
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  • #3
Hello,
What I want to do is leave I(radial) and J(z) as they are in cylindrical coordinates , but change K so that is is not rotating about the z axis. What I want to do is have zero degrees pointing in the +z direction and 180 degrees in the -z direction and 90* at y =0. I drew a crude picture of what I want to do.
20190814_133656.jpg
 
  • #4
Do you mean you want to have the axis of the cylinder along a line you specify? That's also in the FMESH description. Whatever the axis of the cylinder is, theta is defined to be the angle around the circumference of the cylinder.
 
  • #5
No. I do not want theta to be defined as the angle around the circumference of the cylinder. I want theta to be defined as it is in spherical coordinates as the polar angle. Where theta =0 is along the z positive axis and theta = 180 is in the negative z direction.
If it is not possible I can use TMESH just thought it might more elegant to have the mesh and source geometry be the same.
Thanks for your help!
 
  • #6
Oh. Except your first post said you were using a cylindrical source. And you drew a cylinder. If your source is cylindrical then why don't you want theta defined as the angle round the circumference?

If your source is really spherical, sadly FMESH does not have a spherical polar coordinate option.
 
  • #7
Yes the source I am modeling is cylindrical. The formalism I am following dictates that (r,theta) specifies a point relative to the source longitudinal axis. Here is a picture of the geometry that the protocol calls for.

1565818597327.png
 
  • #8
I suppose you could turn the fmesh 90 degrees to the source cylinder. In your drawing you could have the z-axis of the fmesh coming out of the screen. That would give you a circular mesh in the plane of the source. It won't give you the other angle though.
 

1. What is the purpose of changing KMESH/KINTS from azimuthal to polar direction in MCNP6?

The purpose of changing KMESH/KINTS from azimuthal to polar direction in MCNP6 is to improve the accuracy and efficiency of the Monte Carlo simulations. By using a polar direction, the particles are more evenly distributed across the mesh, reducing statistical noise and improving the convergence of the results.

2. How do I change KMESH/KINTS from azimuthal to polar direction in MCNP6?

To change KMESH/KINTS from azimuthal to polar direction in MCNP6, you will need to modify the input file. The "K" card is used to specify the direction of the mesh, and by default, it is set to azimuthal. To change it to polar, add the letter "P" after the "K" on the "KCODE" card. For example, if your original card is "KCODE 1 K", it should be changed to "KCODE 1 KP".

3. What are the limitations of changing KMESH/KINTS from azimuthal to polar direction in MCNP6?

While changing KMESH/KINTS from azimuthal to polar direction can improve the accuracy and efficiency of MCNP6 simulations, it may also increase the computational time and memory requirements. Additionally, it may not be suitable for all types of simulations, such as those involving highly directional sources or complex geometries.

4. Can I change KMESH/KINTS from azimuthal to polar direction during a simulation?

No, you cannot change KMESH/KINTS from azimuthal to polar direction during a simulation. The direction of the mesh is specified in the input file and cannot be modified during the simulation. To change the direction, you will need to modify the input file and rerun the simulation.

5. Are there any other methods for improving the accuracy and efficiency of MCNP6 simulations?

Yes, there are other methods for improving the accuracy and efficiency of MCNP6 simulations. Some options include using variance reduction techniques, optimizing the geometry and mesh, and adjusting the number of particles in the simulation. It is recommended to consult the MCNP6 user manual for more information on these methods and their implementation.

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