# Struggling to understand cell cards in MCNP

#### zincsulphide

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#### PSRB191921

Hi,
you must take all the line "1 1 -1.0 2 -1 4 -3 5 -6"
it means cell number 1 ; material 1 ; Density 1 g/cm3 , after " 2 -1 4 -3 5 -6" is your geometry :
2 is the geometry 2 discribed in the block 2 : it is "PX -5" so it is normal plane to Ox with x=-5. you have +2 so you are on the right of this plane,
-1 is the geometry 1 discribed in the block 2 : it is "PX 5" so it is normal plane to Ox with x=5. you have -2 so you are on the left of this plane,

the instersection of "2 -1 4 -3 5 -6" gives a cube
line 8 is "100 2 -0.001293 (101 -102 -100)"
it means cell number 100 ; material 2 ; Density 0.001293 g/cm3

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I try a scheme :

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#### zincsulphide

Hi,
you must take all the line "1 1 -1.0 2 -1 4 -3 5 -6"
it means cell number 1 ; material 1 ; Density 1 g/cm3 , after " 2 -1 4 -3 5 -6" is your geometry :
2 is the geometry 2 discribed in the block 2 : it is "PX -5" so it is normal plane to Ox with x=-5. you have +2 so you are on the right of this plane,
-1 is the geometry 1 discribed in the block 2 : it is "PX 5" so it is normal plane to Ox with x=5. you have -2 so you are on the left of this plane,

the instersection of "2 -1 4 -3 5 -6" gives a cube
line 8 is "100 2 -0.001293 (101 -102 -100)"
it means cell number 100 ; material 2 ; Density 0.001293 g/cm3
I think I understand it now. So the surface card defines the geometry of each cell, and the cell card has numbers (6 numbers if the model is in 3D) that link to the surface card. Are the 6 cell card numbers in an order like x, x, y, y, z, z? For the last two numbers (5 and -6), why is the second number negative? Both top and bottom of the water phantom are on the +ve z axis. Is it negative because the geometry must be less than pz=20?

Do you mind if I upload an example that I am working on with an attempt at writing the cell and surface cards?

Just one more question. The dimensions of my model are in inches. As 5 inches is 5.08 cm, is it appropriate to round down to 5.0 cm or should I leave numbers exact? In my model I have one cell that is zinc sulphide (with a thickness of 0.0085 cm), so I'm unsure whether to round numbers up/down.

Thanks again!

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#### PSRB191921

So the surface card defines the geometry of each cel
yes

6 numbers if the model is in 3D
no : for a cube you have 6 planes so 6 Numbers. For a sphere one number. For a cylinder 3 Numbers (a cylinder and 2 planes) …

why is the second number negative
if you have a plane (e.g. PX=5) if the number is negative you define all the volume in the direction of -Ox if positive in the direction of Ox. For a sphere negative is the volume Inside the sphere and positive outside the sphere.

Do you mind if I upload an example that I am working on with an attempt at writing the cell and surface cards?
possible

The dimensions of my model are in inches
I Don't know what is "inch" I only used SI (metric) unit

#### zincsulphide

yes

no : for a cube you have 6 planes so 6 Numbers. For a sphere one number. For a cylinder 3 Numbers (a cylinder and 2 planes) …

if you have a plane (e.g. PX=5) if the number is negative you define all the volume in the direction of -Ox if positive in the direction of Ox. For a sphere negative is the volume Inside the sphere and positive outside the sphere.

possible

I Don't know what is "inch" I only used SI (metric) unit
Hi, I will send you a pm of my example because some of the information is from confidential files.

Thanks again

"Struggling to understand cell cards in MCNP"

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