I have a problem on my MCNP5 cross-section library

AI Thread Summary
The MCNP5 cross-section library lacks neutron cross-sections for selenium (Se) and tellurium (Te) with atomic numbers 34000 and 52000, preventing the use of these materials in input files. The discussion highlights that while the natural form of these elements is missing, individual isotopes may be available, allowing users to construct materials from them if present. Suggestions include checking for specific isotopes like 34074, 34076, and others to approximate natural selenium. If isotopes are unavailable, users may need to find suitable substitutes, though this can be complex without data. For those needing these isotopes, exploring online resources and utilizing MCNP's isotope library tools like NJOY is recommended.
Islam Nabil
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i have a problem on my MCNP5 cross-section library
I have a problem with my MCNP5 cross-section library. Se and Te elements with atomic numbers; 34000 and 52000, respectively, have no neutron cross-section stored, either neutron contentious or neutron other, in the library, and so I can't run any input file that has any material of them because of the neutron cross-section.!!
 
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34000 and 52000 indicate the natural form of these elements. That is, it is asking MCNP to look for the natural isotope distribution library for Se and Te. Several of the natural substances are not there while the individual isotopes are there.

Depending what is in your library, you have some choices. If the individual isotopes are there, you could build your material out of them. So, Se for example: https://en.wikipedia.org/wiki/Selenium

You could look in your lib for 34074. 34076, 34077, 34078, 34080, and 34082. If they are all there you can build natural Se out of them. Pretty close, anyway.

If those isotopes are not in your library, you can try to find a material that you can substitute. That's a fairly complicated thing. And it's difficult to be confident if you don't have any data to guide you. Maybe if only some of those isotopes are present, you could build a partial model, maybe using the more common isotopes.

If you are keen, and need these isotopes, and you have the time, you could see if the data exists somewhere on line. Then you could learn the isotope library utils that come with MCNP. NJOY is one of them.
 
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