Questions about the egs_lattice geometry

[ZhouzhouzhouDaxia]

Hello experts,
I tried to use the egs-lattice to build a simulation geometry for test, but the track information and dose information both indicated that the beams could only interact with only one sub geometry at the center of base geometry. The sub geometries were supposed to be placed at different positions based on the description of egs-lattice. Here is the ptracks figure and egsinp code using the egs-lattice. In order to demonstrate the problem, I set vacuum as the material of base geometry. Here is my egsinp code and ptracks figure from egs_view using the egs-lattice. I wonder whether I made a mistake on my script or something goes wrong in the egs-lattice.

###############################################################################
:start geometry definition:
################################### 
:start geometry:
        library  = egs_box
        box size = 1.2e-4 1.2e-4 1.2e-4
        name = world
        :start transformation:
            translation = 0 0 0
        :stop transformation:
        :start media input:
            media = vacuum
        :stop media input:
:stop geometry:

:start geometry:
        library  = egs_spheres
        radii    = 5e-5
        name     = phantom
        :start transformation:
            translation = 0 0 0
        :stop transformation:
        :start media input:
            media = vacuum
        :stop media input:
    :stop geometry:

:start geometry: 
        library  = egs_spheres
        #radii    = 4.4e-8
        radii = 1e-5
        name     = microcavity
        :start media input:
            #media = HfSBU
            media = hf
	    :stop media input:
:stop geometry:

:start geometry:
        library           = egs_lattice
        type              = hexagonal
        name              = phantom_w_microcavity
        base geometry     = phantom
        subgeometry       = microcavity
        subgeometry index = 0
        #spacing           = 1.47e-7
        spacing = 4e-5
:stop geometry:

:start geometry:
        name        = slab
        library     = egs_genvelope
        base geometry = world
        # Inscribed geometries must be strictly inside the envelope
        # No touching of surfaces!
        inscribed geometries = phantom_w_microcavity
:stop geometry:
simulation geometry = slab
:stop geometry definition:

################################
############SOURCE
###################################
:start source definition:
    :start source:
        library = egs_parallel_beam
        name    = the_source
        charge  = -1
        :start shape:
            library = egs_circle
            midpoint = 0 0  
            radius = 5e-5
            :start transformation:
            translation = 0 0 -6e-5
            :stop transformation:
        :stop shape:
        direction = 0 0 1 
        
        :start spectrum:
            type = monoenergetic
            energy = 0.01  # we approximate the Co-60 spectrum by monoenergetic
                           # 1.25 MeV photons
        :stop spectrum:
    :stop source:
    
    
    simulation source = the_source

:stop source definition:


:start media definition: # Only 1 media definition block allowed
# Defining media in the input file like this is called "pegsless" mode
### Cutoff energies, in MeV
ae = 0.512 # lowest energy for electrons (kinetic+0.511)
ap = 0.001 # lowest energy for photons (kinetic)
ue = 50.511 # maximum energy for electrons (kinetic+0.511)
up = 50 # maximum energy for photons (kinetic)

### Water
:start water:
density correction file = water_liquid
:stop water:
#:start water2:
#density correction file = water_liquid
#:stop water2:
### Hafnium
:start hf:
density correction file = hafnium
:stop hf:
:start HfSBU:
density correction file = HfSBU
:stop HfSBU:
:stop media definition:

##################################### Run control
:start run control:
    ncase = 1000000
:stop run control:

##################################### Scoring options
:start scoring options:
    calculation type = dose
    :start calculation geometry:
        geometry name = world
        cavity regions = 0
        cavity mass = 1
    :stop calculation geometry:
    :start calculation geometry:
        geometry name = phantom
        cavity regions = 0
        cavity mass = 1
    :stop calculation geometry:
    :start calculation geometry:
        geometry name = microcavity
        cavity regions = 0
        cavity mass = 1
   :stop calculation geometry:
:stop scoring options:

:start ausgab object definition:

:start ausgab object:
name = tracks
library = egs_track_scoring
score electrons = yes
score positrons = no
score photons = yes
# start scoring = 0 # default is 0
# stop scoring = 1024 # default is 1024
# buffer size = 1024 # default is 1024
:stop ausgab object:

:start ausgab object:
name = dose
library = egs_dose_scoring
dose regions = 0 1 2
volume = 1 1 1
:stop ausgab object:

:stop ausgab object definition:

###################################### Transport parameters
:start MC transport parameter:
      # You can include here any of the transport parameter options
      # understood by EGSnrc
:stop MC transport parameter:

[mchamberland]

Maybe @MartinMartinov can chime in, but I believe this behaviour in egs_view is just an artefact of how egs_lattice is able to transport particles so efficiently. The egs_lattice documentation mentions particles are always scored in the central sub-geometry and dose cannot be distinguished between sub-geometries. So, this is what egs_view is showing you. It does not mean particles are not correctly transported through its sub geometry.

[rtownson]

Thanks @mchamberland I was thinking this too, but your comment reminded me that egs_view only uses howfar, so it should function correctly.

The actual issue is that egs_view shows you the simulation geometry which is set to slab, whereas the particle tracks are just recorded for the last calculation geometry, which is set to microcavity. Since microcavity is just a sphere at the center, that's why you are just seeing tracks from only the center sphere! If you want to simulate the whole geometry, you would have to use a calculation geometry for slab. In egs_ chamber, when you use calculation geometries, the simulation geometry input is ignored (and only used to tell egs_view which geometry to view).

[MartinMartinov]

Reid has the right read on what's happening.

[ZhouzhouzhouDaxia]

Thank you so much! I did make a mistake using the calculation geometry. Now the problem is solved.