MCNP: Declaring two sources in two cells

[lee phong]

Dear all,
I am a new user of MCNP, I have a problem declaring 2 sources F-18 and I-131 in 2 different cells. I only know how to declare each source for each cell, but when combining them into one declaration, I don't know how to do it. Here are my two source declarations. Please help me. Thank

 

[Alex A]

Welcome to physicsforums lee phong!

I don't think there is a real disadvantage to doing two runs with different sources and combining the results. This also has the advantage that some mistakes are easier to spot and if you want to change the source strength of one relative to the other you don't need to rerun the simulation.

If you wrote, or fully understand the F-18 sdef, then you understand everything you need to extend this to a second source. The file uses dependent variables to emit photons, with one probability distribution (d12) and electrons with another (d13), the iodine is a photon source you can rename this to make d14 and add those lines. Then extending SI11 to be L P E P, extend SP11 for the strength. And extend DS10 to DS10 S 12 13 14

Does that make sense? If the iodine was an electron source too it might be SI11 L P E P E, and then all dependent variables of PAR would need 4 entries.

With three entries, you need a dependent variable for POS. DS15 L ax ay az bx by bz cx cy cz
Where a is the position for the F-18 photons, b is the position of the F-18 electrons (the same) and c is the location for the I-131 photon source. In sdef pos becomes pos=fpar=d15 from the default 0 0 0.

You may need another dependent variable for CEL, since the sources seem to be in different cells but it will work exactly the same way.

If anything isn't clear, just ask.

 

[lee phong]

Thank you, for your guidance. This my declaring for the sources:
SDEF PAR= D1 ERG = FPAR = D2 CEL = D3
SI1 L P E P
SP1 1 9.67300E-01 1.93460E+00 $Probality of I-131 & F-18, respective
DS2 S 10 11 12
SI10 L 0.029458 0.029779 0.284305 0.364489 0.636989 0.722911$Photon energy of I-131
SP10 D 0.0138 0.0256 0.0614 0.817 0.0717 0.0177 $ Probality of I-131
SI12 L 5.11000E-01 $Photon energy of F-18
SP12 D 1 $ Prob of photon F-18
SI11 L 2.495E-01 $Mean of electron energy F-18
SP11 D 1 $Prob of electron energy F-18
SI3 L 2 3 $Cell discrible
SP3 D 1 1 $Prob of each cell
This is my describe of the sources. Is it right ? But my outp file noticed "fatal error" with "d1" and "p" in SI1 L P E P.
Please help me

 

[Alex A]

CEL=D3 needs to be a dependent variable, you also don't have a POS yet. SI1 L P E P, is the same as SI1 L 2 3 2. But don't bother to fix this, it can't work in mcnp5. Setting PAR to a distribution works in 6 and X but not in 5. You can have sources in different cells but only one particle type at a time.

Doing two or more runs, multiplying the tallies by the activity of that source and summing the source results is still a good plan. You will need to split the F-18 sdef.

 

[lee phong]

Ok, thank you. I found some problems with MCNP5. My problem with F-18 and I-131 liquid mixing in 2 tanks and each tank has a different ratio volume F-18: I-131. So I separated it into 2 runs with photon energy (insert 511keV of F-18 in I-131) source and electron source of F-18. Also, I describe POS for CEL=D3 and the probability each cell follows the ratio volume. Is that right?

 

[Alex A]

That is right. If you are happy to share your input file, I or people in the forum might be able to offer more advice.

If you want a better simulation you could use volume sources instead of point sources. How complicated this is may depend on the shape of your tanks, and you might need to do more runs to get the final answer.

 

[lee phong]

Great thank for your support