MCNP: Is this a valid way to define "two sources with different sizes"?

[BaoNgoc]

Hi everyone,

I'm a new user MCNP6 and want to define two source cells (cell 1 and cell 5), each with different sizes:

Cell 1 is a large concrete wall (500×400×300 cm)
Cell 5 is a thin granite inside concrete wall (20 cm thick)
Therefore, I want to use different RAD and `EXT` values for each source. I tried this setup:

To implement this, I’m using the following SDEF:
SDEF PAR=2 ERG=d1 L=d10 POS=0 0 0 AXS=0 0 1 CEL=d11 RAD=d12 EXT=d13

And these source distributions:

c ---Source: 1 = cell 1, 2 = cell 5
SI10 L 1 2
SP10 D 0.5 0.5            $ choose probably for each cell
c --- CELL
SI11 L 1 5
SP11 D 0.5 0.5
c --- RAD
SI12 L 420 320
SP12 D 0.5 0.5
c ---  EXT
SI13 L 200 150
SP13 D 0.5 0.5

Is this a valid way to define "two sources with different sizes" in one input file using SDEF?

Thank you very much.

 

[Alex A]

Hi @BaoNgoc,

Welcome to PhysicsForums. I'm a bit confused by L=d10, but I'm fairly sure the answer is no. Random numbers picked independently would be wrong half or more of the time.

There are advantages to doing the sources separately, it's simpler and more flexible. You could also define the source cells to be the same with a union of the cell definitions, but this is a bit 'hacky'.

The proper way to do it is to define dependent variables. Take a look at this example in p387 the manual for MCNP6.3.

SDEF CEL=D1 POS=FCEL=D2
C
SI1 L 101 102 103
SP2 0.4 0.2 0.4
C
DS2 S 4 5 6
C
SI4 L VOLUMER
SP4 1
C
SI5 L .1 .2 .3
SP5 1
C
SI6 L VOLUMER
SP6 1

VOLUMER is an unstructured mesh source. Don't worry about it except that to see that this contains sources in three cells (101 102 and 103) and three source distributions (d4 used in cell 101, d5 used in cell 102 and d6 used in cell 103). These could be point sources or volume sources.