Radioisotope Decay Simulation in MCNP6

[frhnsaif]

TL;DR Summary

Decay of Radionuclide in MCNP6

Hi all
I am a new user of MCNP.I want to simulate radioactive decay of Bi-213 (whole decay chain till stable element) in two concentric spheres of water (let say 5um and 10 um).I want to calculate energy deposited in big sphere(10um) if source is distributed in inner sphere(5 um) .What physics models i need to include in input file. I am specially confused about defining a SDEF.In don't know how to define Source which is emitting alphas and betas at a time with different probabilities.

Thanks
Farhan

 

[Alex A]

Welcome to physicsforums Farhan,

I have a few suggestions, other people may have better advice. You don't need to simulate the electrons and the alphas at the 'same time'. You can do two separate runs, which would get you energy deposited per alpha, and energy deposited per electron then you can multiply by the activity and the electron/alpha probability and sum the result. There are fewer places for mistakes to hide when done this way.

If you need a mixed simulation you can make the PAR variable a distribution. This isn't difficult and would just use probability bins but how energy is locked to a particle I would need to look up.

If you can share your input file, there may be people with a lot more experience than can comment. If so you can rename it to add .txt and the forum will then let you attach it to a post.

 

[frhnsaif]

Thanks for your guidance. Please check appended input and guide
Thanks

 

[Alex A]

That looks fine to me.

 

[frhnsaif]

The problem is absorbed dose calculated is much lower as compared to the GEANT4.In GEANT4 it is in order of 10-2 .but in case of MCNP it is much lower(10-15) order.

 

[Alex A]

What are the units for the GEANT result? With X the result is MeV per gram per source alpha particle and I get values in the 10^8 range. Are you getting a different value?

Sanity check, 10um of water would probably stop alphas, and this and this is 3 orders smaller than 1cm, so 9 orders higher stopping power per gram. This sounds about right.