MCNPX - problem in cross-section

Why does mcnpx not recognize the shell when I crop the cell in half? I put on a lead shield. I put everything (covering everything) and it worked. I cut half and the shield stop of work, but the cell is there.


upload_2019-1-21_13-8-4.png


10 2 -0.9500 (-1 2 -3) #20 imp:p=1 VOL=149.2256511 $ espessura / thickness
20 1 -0.964 (-5 6 -7) imp:p=1 VOL=353.4291735 $ mama / breast
30 3 -0.001205 (-9 -10 11) (1 : -2 : 3 : 5 : -6 : 7) imp:p=1 VOL=20.1061930 $ ar / air
40 4 -11.35 (-12 13 -14 -15) imp:p=1 $ chumbo / Lead
C ----- Acompanhamento -----
80 3 -0.001205 (-80) #10 #20 #30 #40 imp:p=1 $ Mundo-Interno / universe
90 0 (80) imp:p=0 $ Fim do Acompanhamento

C -------------Geometrias / geometries ----------------
C ------------ espessura / thickness ----------
1 cz 8
2 pz -2.5
3 pz 2.5
C ------------ mama / breast -------------
5 cz 7.5
6 pz -2
7 pz 2
C ------------ AR / air -------------
9 cz 8
10 pz 2.7
11 pz 2.5
C ------------ Lead --------
12 cz 8
13 pz 2.75
14 pz 3.75
15 px 0
C --- Fim de Acompanhamento / universe ---
80 SO 225 $ Mundo

area 0 100.53 100.53 0 88.35 88.35 0 100.53 100.53 100.53 0 0 0
mode P $ fotons / photons
C
C -------------- Monoenergetic - conic source ----------------
sc1 raio x monoenergetico para mamografia
SDEF POS=0 0 60 ERG=0.018 PAR=2 VEC=0 0 -1 DIR=d1
SI1 -1 0.991227901 1 $ histogram for cosine bin limits
SP1 0 0.99561395 0.00438605 $ frac. solid angle for each bin
SB1 0 0 1 $ source bias for each bin
 

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Hi,
if I understand your case "complete" you have 1 cm of lead between your source and your calculation cell. For 18 keV photon you have Something like exp(-1000) of attenuation (sorry the NIST site is closed and I don't have the attenuation factor) : It is impossible to have a photon in breast!
In "half" case I think you have diffusion in breast,
 
Hi,
if I understand your case "complete" you have 1 cm of lead between your source and your calculation cell. For 18 keV photon you have Something like exp(-1000) of attenuation (sorry the NIST site is closed and I don't have the attenuation factor) : It is impossible to have a photon in breast!
In "half" case I think you have diffusion in breast,
Thanks for help.

my idea is to close half of the breast to collimate the beam of conical radiation. but it only colimate when put complete lead. when cut de half, he stop the colimation.

What would be diffusion in the breast?
 

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