The process name "Transportation" at boundary means sometimes "Transportation + msc"?

Geometry, Fields and Transportation
1

Dear All,

Nice to meet you.

There’s something I want to confirm.
At the boundary of a substance, there exists an event where the post process is “Transportation” and the momentum reverses before and after that step.
Is it correct to understand this as “Transportation and msc”?

When reading the manual, it feels like “Transportation” and “msc” can occur simultaneously, so I’m thinking that’s what it is.

However, is there an easy way to identify this as “Transportation” and “msc” without selecting events based on the post process being “Transportation” and the momentum being reversed?

Thank you very much in advance,
Kazu

2

When you look at G4StepPoint::GetProcessDefinedStep(), you are seeing only which Discrete or “PostStep” process had the shortest interaction length for that step. There are multiple Continuous processes, including both Transportation and MSC, which are applied AlongStep every time, and there can even be multiple processes (e.g., Decay) which get applied at the end of the step.

When Transportation is reported as GetProcessDefinedStep(), that means that the track reached the boundary of the current volume before any other process’s interaction length was reached.

1 Like
3

Thank you very much, Michael

However, I could not get it completely, yet.

When Transportation is reported as GetProcessDefinedStep(),
that means that the track reached the boundary of the current
volume before any other process’s interaction length was reached.

I had also thought so, but I have few events which I am not getting.
Is it possible to check [Hit 10] in the analysis log?
This shows the Compton scattered recoil electron (Hits information in SD).
Here, x of SD boundary range is -0.025 to 0.025 and gamma is coming from right above.
(x is horizontal, y is vertical, z is gaze direction.)

     |SD|   gamma
     |  |   /
     |  |  /
     |  | / 
     |  |
     |  |
     |  |
     |  |

I hope to hear your opinions, thank you.

From here, analysis log

Event Number (GetEventID() + 1) : 14017

Number of hits : 22
<<<<<<<<<< [Hit 1] <<<<<<<<<<
Track number             : 1
Parent track number      : 0
Track particle ID (name) : 22 (gamma)
prePosition (mm)         : +0.02500, +0.02500, +0.00000
postPosition (mm)        : -0.00699, -0.00699, +0.00000
preMomentum (MeV)        : -2.47487, -2.47487, +0.00000
postMomentum (MeV)       : -2.44376, -1.53763, +0.29707
Pre Energy (MeV)         : 3.50000
Post Energy(MeV)         : 2.90250
Creator process          : NULL
Pre process              : Transportation
Post process             : compt
<<<<<<<<<< [Hit 2] <<<<<<<<<<
Track number             : 1
Parent track number      : 0
Track particle ID (name) : 22 (gamma)
prePosition (mm)         : -0.00699, -0.00699, +0.00000
postPosition (mm)        : -0.02500, -0.01832, +0.00219
preMomentum (MeV)        : -2.44376, -1.53763, +0.29707
postMomentum (MeV)       : -2.44376, -1.53763, +0.29707
Pre Energy (MeV)         : 2.90250
Post Energy(MeV)         : 2.90250
Creator process          : NULL
Pre process              : compt
Post process             : Transportation
<<<<<<<<<< [Hit 3] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : -0.00699, -0.00699, +0.00000
postPosition (mm)        : -0.01013, -0.02354, +0.00071
preMomentum (MeV)        : -0.03111, -0.93725, -0.29707
postMomentum (MeV)       : -0.16611, -0.94351, -0.15707
Pre Energy (MeV)         : 0.59750
Post Energy(MeV)         : 0.58608
Creator process          : compt
Pre process              : NULL
Post process             : msc
<<<<<<<<<< [Hit 4] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : -0.01013, -0.02354, +0.00071
postPosition (mm)        : -0.01279, -0.04047, +0.00476
preMomentum (MeV)        : -0.16611, -0.94351, -0.15707
postMomentum (MeV)       : -0.07540, -0.74280, +0.59045
Pre Energy (MeV)         : 0.58608
Post Energy(MeV)         : 0.56936
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 5] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : -0.01279, -0.04047, +0.00476
postPosition (mm)        : -0.00818, -0.05361, +0.01293
preMomentum (MeV)        : -0.07540, -0.74280, +0.59045
postMomentum (MeV)       : +0.18143, -0.62395, +0.40248
Pre Energy (MeV)         : 0.56936
Post Energy(MeV)         : 0.40843
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 6] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : -0.00818, -0.05361, +0.01293
postPosition (mm)        : +0.00366, -0.06482, +0.01831
preMomentum (MeV)        : +0.18143, -0.62395, +0.40248
postMomentum (MeV)       : +0.22435, -0.62753, -0.33088
Pre Energy (MeV)         : 0.40843
Post Energy(MeV)         : 0.39162
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 7] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.00366, -0.06482, +0.01831
postPosition (mm)        : +0.01032, -0.07698, +0.01837
preMomentum (MeV)        : +0.22435, -0.62753, -0.33088
postMomentum (MeV)       : +0.51036, -0.49042, +0.10526
Pre Energy (MeV)         : 0.39162
Post Energy(MeV)         : 0.36831
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 8] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01032, -0.07698, +0.01837
postPosition (mm)        : +0.01678, -0.08819, +0.02409
preMomentum (MeV)        : +0.51036, -0.49042, +0.10526
postMomentum (MeV)       : -0.10913, +0.23606, +0.65851
Pre Energy (MeV)         : 0.36831
Post Energy(MeV)         : 0.36215
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 9] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01678, -0.08819, +0.02409
postPosition (mm)        : +0.02143, -0.07939, +0.03569
preMomentum (MeV)        : -0.10913, +0.23606, +0.65851
postMomentum (MeV)       : +0.38610, +0.52617, +0.17110
Pre Energy (MeV)         : 0.36215
Post Energy(MeV)         : 0.33536
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 10] <<<<<<<<<< !!! this step finalized by "Transportation", but momentum is largely changed.
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02143, -0.07939, +0.03569
postPosition (mm)        : +0.02500, -0.07452, +0.03727
preMomentum (MeV)        : +0.38610, +0.52617, +0.17110
postMomentum (MeV)       : -0.02942, +0.46865, +0.46471
Pre Energy (MeV)         : 0.33536
Post Energy(MeV)         : 0.32421
Creator process          : compt
Pre process              : msc
Post process             : Transportation
<<<<<<<<<< [Hit 11] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02500, -0.07452, +0.03727
postPosition (mm)        : +0.02484, -0.07072, +0.04137
preMomentum (MeV)        : -0.02942, +0.46865, +0.46471
postMomentum (MeV)       : -0.22240, +0.39813, +0.47340
Pre Energy (MeV)         : 0.32421
Post Energy(MeV)         : 0.32159
Creator process          : compt
Pre process              : Transportation
Post process             : msc
<<<<<<<<<< [Hit 12] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02484, -0.07072, +0.04137
postPosition (mm)        : +0.02239, -0.06872, +0.04719
preMomentum (MeV)        : -0.22240, +0.39813, +0.47340
postMomentum (MeV)       : -0.22173, +0.31015, +0.52269
Pre Energy (MeV)         : 0.32159
Post Energy(MeV)         : 0.31343
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 13] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02239, -0.06872, +0.04719
postPosition (mm)        : +0.02125, -0.06765, +0.05272
preMomentum (MeV)        : -0.22173, +0.31015, +0.52269
postMomentum (MeV)       : -0.22903, +0.12603, +0.58326
Pre Energy (MeV)         : 0.31343
Post Energy(MeV)         : 0.30732
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 14] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02125, -0.06765, +0.05272
postPosition (mm)        : +0.02000, -0.06401, +0.05821
preMomentum (MeV)        : -0.22903, +0.12603, +0.58326
postMomentum (MeV)       : -0.19219, +0.27531, +0.52223
Pre Energy (MeV)         : 0.30732
Post Energy(MeV)         : 0.29310
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 15] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02000, -0.06401, +0.05821
postPosition (mm)        : +0.01835, -0.05911, +0.06204
preMomentum (MeV)        : -0.19219, +0.27531, +0.52223
postMomentum (MeV)       : +0.38575, -0.12003, +0.46121
Pre Energy (MeV)         : 0.29310
Post Energy(MeV)         : 0.28715
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 16] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01835, -0.05911, +0.06204
postPosition (mm)        : +0.02054, -0.05885, +0.06741
preMomentum (MeV)        : +0.38575, -0.12003, +0.46121
postMomentum (MeV)       : -0.46698, +0.04818, +0.37397
Pre Energy (MeV)         : 0.28715
Post Energy(MeV)         : 0.27727
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 17] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02054, -0.05885, +0.06741
postPosition (mm)        : +0.01694, -0.06022, +0.07402
preMomentum (MeV)        : -0.46698, +0.04818, +0.37397
postMomentum (MeV)       : -0.30323, -0.27443, +0.40449
Pre Energy (MeV)         : 0.27727
Post Energy(MeV)         : 0.25841
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 18] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01694, -0.06022, +0.07402
postPosition (mm)        : +0.01523, -0.06552, +0.07749
preMomentum (MeV)        : -0.30323, -0.27443, +0.40449
postMomentum (MeV)       : +0.16035, -0.53758, +0.08627
Pre Energy (MeV)         : 0.25841
Post Energy(MeV)         : 0.25272
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 19] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01523, -0.06552, +0.07749
postPosition (mm)        : +0.01414, -0.07222, +0.08048
preMomentum (MeV)        : +0.16035, -0.53758, +0.08627
postMomentum (MeV)       : +0.03122, -0.20754, +0.51403
Pre Energy (MeV)         : 0.25272
Post Energy(MeV)         : 0.24359
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 20] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01414, -0.07222, +0.08048
postPosition (mm)        : +0.01784, -0.07340, +0.08658
preMomentum (MeV)        : +0.03122, -0.20754, +0.51403
postMomentum (MeV)       : +0.44141, -0.12257, +0.28783
Pre Energy (MeV)         : 0.24359
Post Energy(MeV)         : 0.23320
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 21] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.01784, -0.07340, +0.08658
postPosition (mm)        : +0.02344, -0.07527, +0.08708
preMomentum (MeV)        : +0.44141, -0.12257, +0.28783
postMomentum (MeV)       : +0.49540, -0.13363, +0.12782
Pre Energy (MeV)         : 0.23320
Post Energy(MeV)         : 0.22435
Creator process          : compt
Pre process              : msc
Post process             : msc
<<<<<<<<<< [Hit 22] <<<<<<<<<<
Track number             : 2
Parent track number      : 1
Track particle ID (name) : 11 (e-)
prePosition (mm)         : +0.02344, -0.07527, +0.08708
postPosition (mm)        : +0.02500, -0.07569, +0.08748
preMomentum (MeV)        : +0.49540, -0.13363, +0.12782
postMomentum (MeV)       : +0.38198, -0.02778, +0.36300
Pre Energy (MeV)         : 0.22435
Post Energy(MeV)         : 0.22356
Creator process          : compt
Pre process              : msc
Post process             : Transportation

==============================================================
analysis log end.


FYI, most data are like following...

Event Number (GetEventID() + 1) : 1
Number of hits : 1
<<<<<<<<<< [Hit 1] <<<<<<<<<<
Track number             : 1
Parent track number      : 0
Track particle ID (name) : 22 (gamma)
prePosition (mm)         : +0.02500, +0.02500, +0.00000
postPosition (mm)        : -0.02500, -0.02500, +0.00000
preMomentum (MeV)        : -2.47487, -2.47487, +0.00000
postMomentum (MeV)       : -2.47487, -2.47487, +0.00000
Pre Energy (MeV)         : 3.50000
Post Energy(MeV)         : 3.50000
Creator process          : NULL
Pre process              : Transportation
Post process             : Transportation

Event Number (GetEventID() + 1) : 2
Number of hits : 1
<<<<<<<<<< [Hit 1] <<<<<<<<<<
Track number             : 1
Parent track number      : 0
Track particle ID (name) : 22 (gamma)
prePosition (mm)         : +0.02500, +0.02500, +0.00000
postPosition (mm)        : -0.02500, -0.02500, +0.00000
preMomentum (MeV)        : -2.47487, -2.47487, +0.00000
postMomentum (MeV)       : -2.47487, -2.47487, +0.00000
Pre Energy (MeV)         : 3.50000
Post Energy(MeV)         : 3.50000
Creator process          : NULL
Pre process              : Transportation
Post process             : Transportation

Event Number (GetEventID() + 1) : 3
Number of hits : 1
<<<<<<<<<< [Hit 1] <<<<<<<<<<
Track number             : 1
Parent track number      : 0
Track particle ID (name) : 22 (gamma)
prePosition (mm)         : +0.02500, +0.02500, +0.00000
postPosition (mm)        : -0.02500, -0.02500, +0.00000
preMomentum (MeV)        : -2.47487, -2.47487, +0.00000
postMomentum (MeV)       : -2.47487, -2.47487, +0.00000
Pre Energy (MeV)         : 3.50000
Post Energy(MeV)         : 3.50000
Creator process          : NULL
Pre process              : Transportation
Post process             : Transportation

Thank you for reading,

4

I would like to add Geant4 version and Physics List, just in case.

**************************************************************
 Geant4 version Name: geant4-11-00 [MT]   (10-December-2021)
                       Copyright : Geant4 Collaboration
                      References : NIM A 506 (2003), 250-303
                                 : IEEE-TNS 53 (2006), 270-278
                                 : NIM A 835 (2016), 186-225
                             WWW : http://geant4.org/
**************************************************************

<<< Geant4 Physics List simulation engine: FTFP_BERT

Best regards,
Kazu

5

Hi Kazu,

For every step that Geant4 simulates for a charged particle we expect both multiple scattering and ‘transportation’ (a ‘process’ that sees the geometry boundaries) to be active. In the case of multiple scattering it will alway propose a change in the particle’s direction (except if the step length was zero).

The transportation examines whether a boundary exists before the shortest length which physics processes indicate they will occur - for discrete interactions. ( Not that for some process implementations it could indicates just that its approximations are only good for this length.). If it finds such a boundary before the ‘shortest physics limit’, it will ‘win’ the contest to determine the size of the current step. Nevertheless other Geant4 processes whose effect is cumulated along the step, including multiple scattering in particular, will be given the chance to effect the state of the track - contributing to the final momentum direction and energy.

So indeed in the case of ‘Hit[10]’ the Transportation found the boundary, and the Multiple scattering proposed a change in direction which meant that the particle ‘bent back’ into the current volume.

6

Dear John and Mike,

With your guidance, I’ve gained a deeper understanding for Geant4. Thank you!

I was checking the behavior of electrons leaving the SD.
So, at first, I felt that if it’s coming back inwards, it should be labeled as “msc” rather than “Transportation”.
But now I think this might just be due to my lack of experience with Geant4.

I appreciate the invaluable insights you provided, thanks again!

Best regards,
Kazu