MCNP6.2 - SDEF position related keywords

[19matthew89]

TL;DR

It's unclear whether SDEF position related keywords could be dependent on POS

Hi everyone,

I have started delving into the "nightmare" of source definition and in my opinion, the MCNP manual here sounds even more cryptic and obscure than in other sections.

By the way, I have a question related what is reported in paragraph 5.8.1 of the MCNP® Code Version 6.3.0 Theory & User Manual. It says:
"None of the position-related keywords (i.e., CEL, SUR, RAD, AXS, EXT, X, Y, Z, and CCC) can be a dependent distribution of POS."
So from what I understand, none of the position-related keyword could be defined as dependent on POS, so namely expressions like "EXT=FPOS=D1" or "RAD=FPOS=D1" are not legit.

However, there are examples of this use.

For instance in the manual itself: the Example 10 (paragraph 5.8.6..10 at page 402) defines the source as

SDEF PAR=SF CEL=D1 POS=D2 RAD=FPOS=D3

.

So, according to your experience, is the command allowed and works? I ask because, I plan to define a pretty complicated surface source and at the moment the most intuitive way of defining it would be exactly via a FPOS.

Thanks a lot in advance

 

[Grelbr42]

My suggestion is to give it a whirl and use ptrac to see where the first thousand or so particles are created. Maybe you don't have to use the complete complicated source you intend for your final situation, just enough to demo that it will or will not work as you need.

 

[PSRB191921]

@19matthew89
yes you can use Fpos with MCNP "parameters depend of the position"
for example you want to simulate a source whose energy depends on the position you can write:

sdef pos=d1 par=p erg=fpos=d2
si1 L 0 0 0 0 0 10
sp1 1 1
DS2 S 3 4 $ energy is function of position
SI3 L 1.17 1.33 $ in (0,0,0) energy= 1.17 and 1.33 MeV
SP3 1 1
SI4 L .511 $ in (0,0,10) energy=511 keV
SP4 1

It is a simple example. You can imagine fpos for rad, cel, ...
hope your supervisor is ok with that

 

[19matthew89]

@19matthew89
yes you can use Fpos with MCNP "parameters depend of the position"
for example you want to simulate a source whose energy depends on the position you can write:

sdef pos=d1 par=p erg=fpos=d2
si1 L 0 0 0 0 0 10
sp1 1 1
DS2 S 3 4 $ energy is function of position
SI3 L 1.17 1.33 $ in (0,0,0) energy= 1.17 and 1.33 MeV
SP3 1 1
SI4 L .511 $ in (0,0,10) energy=511 keV
SP4 1

It is a simple example. You can imagine fpos for rad, cel, ...
hope your supervisor is ok with that

Thanks a lot! I will try it straightaway!
I'll check anyway the origin of particles via the Table 110 to be sure!
Absolutely...my supervisor is totally ok with that ;)

So...what about the comment in the manual then? What does it mean?
I ask also because, poring over the topic, I found this paper too (https://www.sciencedirect.com/science/article/pii/S0306454907001788) where the author caustically complains (section 3 and 4) that FPOS is misbehaving and not working.