# MCNP Cylindrical Phantom Calculation Help

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1. Apr 22, 2017

### Mark Hamil

I'm new to mcnp and trying to perform this calculation, if anyone can provide some feedback to see if I'm even going in the right direction that would be much appreciated. The geometry is correct with only 1 transverse, the issue I am having is making sure my data block is correct and how I am to determine my output. This is the calculation, my code, and output. I've been going from the manual which has taken some time.

Calculation:
Auxier et al. performed computations of dose coefficients for NCRP 38 using a cylindrical phantom that was 30 cm in diameter by 60 cm tall. Portions of NCRP 38 have been copied as well as a part of an associated article in the reference book Radiation Dosimetry. The portion of Auxier’s book is provided as a reference which justifies the methods used in NCRP 38. Once he computed the maximum absorbed dose and dose equivalent in the cylinder for a given energy, he converted it to a dose coefficient by dividing by the fluence that was incident on the cylinder. You are to redo the computations from NCRP 38. You will then modify the methods used in NCRP 38 and perform some additional calculations. In NCRP38, the absorbed dose was calculated in parallelepipeds that are 2 cm x 5 cm x 30 cm.
Assignment: Compute the absorbed dose coefficients in the volume elements using Auxier’s compositions. Use the dose tallying volumes as described by Traverse 1 in NCRP 38. Using the +F6 tally is the quickest way to do this. Perform those computations for the following 4 neutron energies:
a. 1 keV b. 1 MeV c. 10 MeV d. 50 MeV
Compare your results with NCRP38 results. Note this will require you to divide the computed dose by the fluence incident on the phantom surface. The +F6 requires a MODE P E N H D T S A # to ensure that all the particles are tracked. An *F8 would give absorbed dose as well but tracks every particle in detail. The +F6 basically looks at the energy of the particles entering and leaving a volume and computes dose by the differences.

Code:
Cylindrical Phantom
c *********************Cell Block*************************************
17 0 16
18 5 -1 (-16 #(-1 -16) #(-2 -16) #(-3 -16) #(-4 -16) #(-5 -16) #(-6 -16)
#(-7 -16) #(-9 -16) #(-10 -16) #(-11 -16) #(-12 -16) #(-13 -16)
#(-14 -16) #(-8 -16) #(-15 -16))
19 5 -1 -1
20 5 -1 -2
21 5 -1 -3
22 5 -1 -4
23 5 -1 -5
24 5 -1 -6
25 5 -1 -7
26 5 -1 -16 -8
27 5 -1 -9
28 5 -1 -10
29 5 -1 -11
30 5 -1 -12
31 5 -1 -13
32 5 -1 -14
33 5 -1 -16 -15

c ********************Surface Block***********************************
16 RCC 0 0 0 0 0 60 15
1 RPP -2.5 2.5 -1 1 15 45
2 RPP -2.5 2.5 -3 -1 15 45
3 RPP -2.5 2.5 -5 -3 15 45
4 RPP -2.5 2.5 -7 -5 15 45
5 RPP -2.5 2.5 -9 -7 15 45
6 RPP -2.5 2.5 -11 -9 15 45
7 RPP -2.5 2.5 -13 -11 15 45
8 RPP -2.5 2.5 -15 -13 15 45
9 RPP -2.5 2.5 1 3 15 45
10 RPP -2.5 2.5 3 5 15 45
11 RPP -2.5 2.5 5 7 15 45
12 RPP -2.5 2.5 7 9 15 45
13 RPP -2.5 2.5 9 11 15 45
14 RPP -2.5 2.5 11 13 15 45
15 RPP -2.5 2.5 13 15 15 45

c ********************Data Block**************************************
m5 1000 6.169 $Hydrogen Mass Fraction 6000 1.258$ Carbon Mass Fraction
7000 0.107 $Nitrogen Mass Fraction 8000 2.333$ Oxgen Mass Fraction
c Sourse card
IMP:N 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
SDEF pos=0 0 0 x=d1 y=20 z=d2 vec=0 1 0 dir=-1 par=1 erg=0.001
si1 -15 15
sp1 0 1
si2 0 60
sp2 0 1
c
c Tallies
c
MODE N H D T S A #
f6: N P 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
E0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Output:
For my output Im going in to the MCNP command window. The file is in my desktop. I'm typing
cd desktop
mcnp6 i=calculation(this is the file name)
and it gives this

cd desktop

mcnp6 i=project
mcnp ver=6 , ld=05/08/13 04/22/17 12:43:44
Code Name & Version = MCNP6, 1.0
Copyright LANS/LANL/DOE - see output file

_/ _/ _/_/_/ _/ _/ _/_/_/ _/_/_/
_/_/ _/_/ _/ _/_/ _/ _/ _/ _/
_/ _/ _/ _/ _/ _/ _/ _/_/_/ _/_/_/
_/ _/ _/ _/ _/_/ _/ _/ _/
_/ _/ _/_/_/ _/ _/ _/ _/_/

warning. Physics models enabled.
error: searched directories:
.

C:\cygwin\MCNP_DATA

Expire parameter is data file pelxs.dat does not exist.

bad trouble in subroutine bcd_file_in of imcn

data file pelxs.dat does not exist.

2. Apr 23, 2017

### PSRB191921

Dear Mark,
First you have a cross-section problem : in "mode n" you cannot write a material "ZZ000" but "ZZAAA" (for example 8016 and not 8000).
Second I think that Aussier et al. and NCRP are old references. Why not used ICRP for dose calculation. You can also read, for more explanation the book "Antoni and Bourgois applied physics of external Radiation exposure : Dosimetry and Radiation Protection, Springer, 2017"
Third You must have an importance (imp) at 0 (end of transport)
Regards
PSR