Particles lost in MCNP running

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Discussion Overview

The discussion revolves around issues encountered in a Monte Carlo N-Particle Transport Code (MCNP) simulation, specifically regarding particles being lost in air bubbles within a defined geometry. Participants are examining the geometry definitions and cell configurations to identify and resolve the problems causing particle loss.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports that particles are lost in air bubbles, indicating problems with specific cell definitions (cells 1500-1504, 2-7, and 1300).
  • Another participant suggests that the definition of cell 1300 is failing, leading to particles being lost, and provides a specific format for defining the space between coordinates.
  • There is a reiteration of the need to use the union operator correctly when defining spaces, with references to Boolean logic and De Morgan's theorem.
  • A participant mentions that the user's manual advises against frequent use of the complement operator, but they find it necessary to pass geometric tests despite errors reported by the software.
  • Concerns are raised about the complexity and potential errors in the input file, with a specific mention that cell 1504 is actually a surface and not defined as a cell.

Areas of Agreement / Disagreement

Participants express differing views on the correct approach to defining cells and spaces, with some suggesting specific definitions while others point out potential errors in the current setup. The discussion remains unresolved regarding the best method to correct the issues.

Contextual Notes

Participants note that the input file is complicated and may contain multiple errors, with specific references to the definitions of cells and surfaces that could be contributing to the problems.

flashcflash
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Hi dears,
My model has several air bubbles to surrounding solid models. The output file reported some particles were lost in my air bubbles and could not find a cell there. I have used vised to check and found that cell 1500-1504,cell2-7,cell1300 has some problems. I changed the geometry definitions from planes to macro rectangles, but the errors persist. Any advice would be helpful. Thank you!

Attachment is output file with source code.
 

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Cell 1300 is the big cell containing the experiment and air, outside that is the void cell. That cell definition is failing and anything going into the space that should be cell 1300 is getting lost. When defining a space in a box you want the space between x1 and x2, y1 and y2, z1 and z2 so the definition reads like +x1 -x2 +y1 -y2 +z1 -z2
When defining the outside of that space you can't just flip the tests, you have to use the union operator :
People that have done Boolean logic might recognize this as De Morgan's theorem in action. -x1 +x2 would straight away be a space that doesn't exist, it's below a lower value and at the same time above a higher value.

What is needed is -x1:+x2:-y1:+y2:-z1:+z2
ie, all the space below the lower bounds and also all the space above the higher bound for every axis.
 
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Alex A said:
Cell 1300 is the big cell containing the experiment and air, outside that is the void cell. That cell definition is failing and anything going into the space that should be cell 1300 is getting lost. When defining a space in a box you want the space between x1 and x2, y1 and y2, z1 and z2 so the definition reads like +x1 -x2 +y1 -y2 +z1 -z2
When defining the outside of that space you can't just flip the tests, you have to use the union operator :
People that have done Boolean logic might recognize this as De Morgan's theorem in action. -x1 +x2 would straight away be a space that doesn't exist, it's below a lower value and at the same time above a higher value.

What is needed is -x1:+x2:-y1:+y2:-z1:+z2
ie, all the space below the lower bounds and also all the space above the higher bound for every axis.
Thank you, that must be the mislead of user's manual. It said I should seldom using complement operator. Not only the last cell, several of them have problem. The vised would report error in red lines even using union operator, the complement operator for cell combination is the only way to pass the geometric test.
 
All space in the problem must belong to a cell, and no point in space may belong to more than one cell.

That is a complicated input file and it's a bit of a mess. You mention cell 1504, but there is no cell 1504, there is a surface 1504 and it isn't used in any of the cell definitions.

Is there a working version of this you are modifying or did you make the whole thing from scratch?
 

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