"10 particles lost" warning in MCNPX

[Nour_wahban]

TL;DR Summary

hello! i'm working on a landmine detection using neutron technique and the model involves using a ring detector i did my best to understand its part but i'm getting this error and the tally counts are not correct. I attached the input file if someone could help!

 

[Alex A]

Welcome to PhysicsForums @Nour_wahban,

The source is at 0 53 0. Surface 20 is defined as py 53. Never make a point source coincident with a surface. Even surfaces made by a macrobodies and even when they extend beyond the cell they define. Changing to POS=0 52.5 0 solves that error for me. I do not know how ring detectors work, if the tally is still wrong post more information and hopefully someone will know.

Suggest you define the void as "3 0 23", just because it's simpler.

Edit, btw your BPE doesn't surround your PE moderator, how big are the BPE and PE supposed to be?

 

[Nour_wahban]

Welcome to PhysicsForums @Nour_wahban,

The source is at 0 53 0. Surface 20 is defined as py 53. Never make a point source coincident with a surface. Even surfaces made by a macrobodies and even when they extend beyond the cell they define. Changing to POS=0 52.5 0 solves that error for me. I do not know how ring detectors work, if the tally is still wrong post more information and hopefully someone will know.

Suggest you define the void as "3 0 23", just because it's simpler.

Edit, btw your BPE doesn't surround your PE moderator, how big are the BPE and PE supposed to be?

Thank you for the reply, I edited the part of the source, and it works now but still gives me a tally warning "
warning. tally 4 tfc bin did not pass 2 of 10 statistical checks.
warning. 1 of 1 tallies did not pass all 10 statistical checks.
warning. 1 of 1 tallies had bins with large relative errors. "
for the part of BPE it should 5 cm radius with 2.5 cm height while PE is 2.5 cm radius and 5 cm height.

The model goal is to count back scattered neutrons on the ring detector and I'm still struggling how to model this properly.

EDIT, I changed the tally to f4 and added a ring detector cell since the output of f5 is not working properly. but unfortunately, it's not giving me a correct output also. I attached an image with the curve i'm trying to plot to validate this model and the new input file.

 

[Alex A]

"17 cy 5 $PE
18 cy 2.5 $BPE"
These definitions are backwards, swap 17 and 18. This probably isn't the cause of your problems.

Statistical errors are usually an indication too few particles are making it to the detector. Having multiple rings in the problem and running a higher nps might help to get a lot of results with the same compute and better stats.

What are your results and how are you working out the answer?