About the example "4.2 Create an egs++ input file", i really don't understand why some programming mean?

[kstcmcjw]

Hello each elder of EGSnrc, About the example "4.2 Create an egs++ input file", i really don't understand why some programming mean. There are some problom pozzled me.

1. Why Z-planes has four numbers? X and Y position only has two? Three-dimensional graphics depend on the beginning and end of each direction to draw three-dimensional graphics, Why are there four points on the Z-Plane?
   

2. As we have define the energy of photons or electrons in 20MeV , why the "Media" has the cutoff energies? I think the maximum energy is 20MeV
   

3. And the figure only see the Ta plate , lack we have define the lead and the water's simulation?

i can't find where the "lead" the "water" is? and there is no lead and water in this figure!

4. The EGSnrc program’s execute interface after start, execution failed, and there is NO batch, why? i was really puzzled!

my slab.egsinp programming is:

###1.Run control
:start run control:
    ncase = 1e3
:stop run control:

###2.Geometry
:start geometry definition:
    :start geometry:
        name = slab
        library = egs_ndgeometry
        type = EGS_XYZGeometry
        x-planes = -5, 5 
        y-planes = -5, 5  
        z-planes = -10, 0, 0.1, 10
        :start media input:
            media = vacuum tantalum
            set medium = 1 1
        :stop media input:
    :stop geometry:
    simulation geometry = slab
:stop geometry definition:

###3.Media
:start media definition:
    ae = 0.521  
    ap = 0.01                   
    ue = 50.511                                
    up = 50                               
   
    :start tantalum:
          density correction file = tantalum
    :stop tantalum:

    :start lead:
          density correction file = lead
    :stop lead:

    :start water:
          density correction file = water_liquid
    :stop water:

:stop media definition:

###4.Source
:start source definition:

    pencil beam
    :start source:
        name = pencil_beam
        library = egs_parallel_beam
        charge = -1
        direction = 0 0 1
        :start spectrum:
            type = monoenergetic
            energy = 20                         
        :stop spectrum:
        :start shape:
            type = point
            position = 0 0 -10                  
        :stop shape:
    :stop source:
    simulation source = pencil_beam

:stop source definition:

###5.VIEWER CONTROL
:start view control:
    set color = lead 120 120 200 200
    set color = tantalum 120 255 120 255
    set color = water 0 220 255 200
:stop view control:

###6.AUSGAB OBJECTS
:start ausgab object definition:
    :start ausgab object:
        name = tracks
        library = egs_track_scoring
    :stop ausgab object: 
:stop ausgab object definition:

Thanks for your attention and answers!

[rtownson]

1. The 4 number define 3 regions, or 3 slabs where you can define a material. Between -10 and 0 is vacuum, between 0 and 0.1 is tantalum, and between 0.1 and 10 is vacuum. If you only defined between 0 and 0.1, then you would not see particle tracks anywhere outside the tantalum track, because the space is not defined! Particles outside any defined regions are discarded.
2. The media have independent cut-off energies because you may wish to change them for some more advanced studies. There is no reason to have them larger than your maximum energy in the simulation, so you could indeed reduce them to 20.511 and 20 MeV. However, there is little harm to having them a bit too large, the main effect is that it expands the interpolation grid (so don't have AE and AP at 100 MeV for simulations at 100keV).
3. It is possible to define materials that are not used in the simulation. In this case, yes there are some extra materials defined and not used. A material is only included in the simulation if it is actually assigned to a geometry region, as is the case for tantalum (where you see set medium = 1 1.
4. I copy/pasted your input file and it ran fine using egs_app for me. Can you try with egs_app instead of myapp? You may have to compile the application first. If it still fails, copy/paste all the output so I can look for other errors. Have you have any simulations run successfully yet? Try the existing example slab.egsinp in egs_home/egs_app.

[rtownson]

I see, I had forgotten that you saw this error from the start. Did you try with egs_app instead of myapp like I suggested? I'm not sure why you are seeing this error. Do you get any additional information with the error when you launch the simulation from the command line instead of using egs_gui?

[kstcmcjw]

Yesterday, i had a try of egs_app but failed, OK, i will have a try once more, and make printscreen step by step, by the way, your said egs_app is in this folder?

This is the running reslut:

Is my software will re-install? Or have something wrong?

[rtownson]

Yes that's the right folder. Did you compile egs_app first?

[kstcmcjw]

i first use the EGS_gui to run it, and as you see, whether i should use the cmd window?

[rtownson]

Since it seems like the simulation is actually running correctly, I would try running it using the command window to see if it gives you any extra output. Sometimes it will show slightly more information.

[kstcmcjw]

And i have another question: as we know, over 10MeV photon or electron have a collision with material may cause neutron, duo to photonuclear reaction. But in our experiment, simulation energy to 20MeV, but there seems no neutron created or mentioned, why? Whether the EGS software only simulation the elecrton, positron and photon except the other particles?

[rtownson]

EGSnrc can model photonuclear attenuation if you set the transport parameter: Photonuclear attenuation = On. By default it is off. However, EGSnrc does not actually simulate the transport of neutrons; only photons, electrons and positrons. So you will not see neutrons in the particle tracks.