Simulation of Pu-238 Decay

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SUMMARY

This discussion focuses on simulating the decay of Pu-238 using MCNP6.1.1b, specifically addressing the complexities encountered with the F6 tally and the SDEF card configurations. The user reports an output of 0.21667 MeV per gram, resulting in a total decay heat of only 22 watts, significantly lower than the expected 62.5 watts for a Pu-238 pellet. A suggestion was made to remove the ACT option and use PAR=sa to ensure accurate alpha decay information is utilized, which may resolve the discrepancies in the simulation results.

PREREQUISITES
  • Understanding of MCNP6.1.1b simulation software
  • Familiarity with F6 tally and SDEF card configurations
  • Knowledge of alpha decay processes and related parameters
  • Basic principles of radioactive decay heat calculations
NEXT STEPS
  • Investigate the functionality of PAR=sa in MCNP6.1.1b
  • Learn about the implications of removing the ACT option in MCNP simulations
  • Research the correct setup for F6 tally in radioactive decay simulations
  • Explore decay heat calculations for different isotopes, focusing on Pu-238
USEFUL FOR

Students and researchers in nuclear physics, particularly those working on simulations of radioactive decay and energy production from isotopes like Pu-238 in radioisotope thermoelectric generators (RTGs).

omarkhairallah
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Hi everyone, In my graduation project i am trying to simulate the decay of Pu-238 (in RTGs) and the dose from it on mcnp6.1.1b. I used the F6 tally and (PAR=sa) in the SDEF card to simulate the decay of alphas and also set the mode to ( MODE a e p ) to put the gammas and betas in consideration ( if any interactions could produce one of them and contribute to the total dose).

But i am facing some complexities, when using the F6 tally, the output is 0.21667 Mev per gram, which is when multiplied by the grams of the cell (145.6) and converting to watts, it's only 22 watts while the pellet of Pu-238 should produce 62.5 watts (In one RTG pellet) of decay heat, i want someone to help me with this because i dont know what's wrong.

You can find my input file attached.
 

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Hi @omarkhairallah,

Welcome to PhysicsForums.

I don't know what par=sa actually does. It's new in 6.1.1 and it looks up alpha decay information from decay tables and CINDER. I don't understand ACT either. When I use par=a erg=5.5 and remove ACT to make it run on my version the tally when multiplied by the mass is 5.4999 MeV. Which is trivially what it should be. Try removing ACT and if that doesn't fix it then the spontaneous alpha option isn't doing what you think it is.
 
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