Using scoring commands changes optical surfaces?

Recording, Visualizing and Persisting Data
1

I created a simple project to simulate the expected non-uniform response in a plastic scintillator tile read out by two SiPMs attached to wavelength shifting bars. I created a setup with the panel and WLS bars with the appropriate optical surfaces, and did a sanity check in a visualization. So far, so good. The scintillation light is generated, is partially attenuated in the panel, and is trapped in the WLS bars.

To check the result more quantitatively, I added some scoring meshes to the ends of the bars where I want the SiPMs to be. I’m still learning in regards to using the scorers, so I started by prototyping with the commands interactively. Now if I place a scorer, draw it, and run a new event, the visualization changes drastically. Specifically, it seems like the optical surface properties of my volumes change. The scintillation light is no longer reflecting inside the panel, but passes straight through it as if there were no wrapping.

For instance, I open a gui session and run
/gps/particle mu-
/gps/energy 3 GeV
/run/beamOn 1

I then add a scorer and run again:
/score/create/boxMesh sipm1
/score/mesh/boxSize 7.5 7.5 0.5 mm
/score/mesh/nBin 1 1 1
/score/mesh/translate/xyz 27.005025253169418 28.065685424949237 0 cm
/score/mesh/rotate/rotateZ 45 deg
/score/mesh/rotate/rotateX 90 deg
/score/quantity/flatSurfaceCurrent sipm1current 1 0 0
/score/filter/particle phot opticalphoton
/score/close
/run/beamOn 1

On the left is the run before the scoring mesh is added, on the right is after. This is the only change I have made:

scoring_comparison
scoring_comparison1200×575 18.9 KB

Can anyone help me understand why this is happening? I can probably get the information I want out of the simulation without the scoring, but I would rather learn how to use the built-in tool for future projects.

Thanks for any help!

2

This sounds like this bug:

https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2113

which was fixed for 10.6. Which Geant4 version are you using? If earlier than 10.6 could you please try 10.6.

3

Hi Daren,

Thank you!

This was the culprit. I hadn’t upgraded since 10.5.0. Installed 10.6.2 and this problem disappears.

4

Hi, I’m trying to simulate a scintillator with a reflective skin, however when I place a scorer touching the surface of the crystal I get this error:

-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : OpBoun06
      issued by : G4OpBoundaryProcess
G4OpBoundaryProcess: Opticalphoton step length: 7.84205e-09 mm.
This is larger than the threshold 1e-09 mm to set status StepTooSmall.
Boundary scattering may be incorrect. 
*** Step size warnings stopped.

*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------

Could you help me understand what you did in order to get the photons out of the crystal and into de scorers?

5

This warning can almost definitely be ignored.

If you still have problems could you please open a new thread.

6

I tried to ignore it, but my scorers are not collecting hits. I also opened a new thread right before writing my previous answer, here is the link Scintillation scorer.

7

Ok, let’s continue the discussion in that thread.