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Question bug in tracking through concentric spherical layers? 

Forum: Geometry
Date: 15 Jan, 2009
From: Scott Nutter <Scott Nutter>

This message was originally posted in the tracking category and was requested to be moved here.

I have a model of the atmosphere consisting of layers of concentric hollow spheres of different densities (so sphere radii are very large). I think there is a problem with tracking at the surface of a large sphere when particles are normally incident. I start TeV electrons at the top of the atmosphere (400 km). When sending an electron in any direction except straight down, tracking occurs as expected through the successive layers. If straight down, the electron is sent to OutofWorld at the boundary between the first and second layers.

My layers are defined as concentric hollow spheres, with the inside and outside radii defined in the table below (spere radius). They all are placed inside the world volume "atmosphere." (Note that the inside radius of one sphere = outside radius of next smaller sphere, etc. The number of digits shown below may not reflect that.)

I recall an issue with tracking on spheres in the user's guide with the suggestion that a small gap be placed between layers to ensure proper tracking. I tried 1 micron above and below each layer in place, with no change, and increasing that gap does not help. The problem is still present for straight down electrons for larger gaps and any energy.

Specifics:  G4.9.2 (problem was there for 4.9.1.p03)
PhysicsList is from examples/electromagnetic/TestEm16.  All physics is turned off via the individual /process/inactivate commands.
Geometry (last few layers of atmosphere):
layer#    height above    sphere radius (km)   density
          Earth (km)       REarth+Height       (g/cm3)
372       95.091196862     6473.2281969     1.3831442574e-06
373       239.68927398     6617.826274      1.7531558941e-17
374       289.68927398     6667.826274      3.8538387204e-21
375       339.68927398     6717.826274      1e-22
376       389.68927398     6767.826274      1e-22
377       400              6778.137         1e-22

Electrons start at 400 km (top of layer 377) going down into layer 376, etc. Tracking output for a straightdown electron:

*********************************************************************************************************
* G4Track Information:   Particle = e-,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0        0        0 6.78e+09     1e+05        0        0         0 atmlayer376 initStep
    1        0        0 6.77e+09     1e+05        0 1.03e+07  1.03e+07  OutOfWorld Transportation
1 events processed

A normal event at incidence angles other than vertical will continue to track through the variable thickness layers (first few steps shown below for off-vertical incident track):

*********************************************************************************************************
* G4Track Information:   Particle = e-,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0        0        0 6.78e+09     1e+05        0        0         0 atmlayer376 initStep
    1 1.44e+07 -1.04e+07 6.77e+09     1e+05        0 2.05e+07  2.05e+07  atmosphere Transportation
    2 1.44e+07 -1.04e+07 6.77e+09     1e+05        0        0  2.05e+07 atmlayer375 Transportation
    3 8.53e+07 -6.14e+07 6.72e+09     1e+05        0 1.01e+08  1.22e+08 atmlayer374 Transportation
    4 1.58e+08 -1.14e+08 6.66e+09     1e+05        0 1.03e+08  2.25e+08 atmlayer373 Transportation
    5 2.32e+08 -1.67e+08 6.61e+09     1e+05        0 1.06e+08  3.31e+08 atmlayer372 Transportation
    6  4.6e+08 -3.31e+08 6.45e+09     1e+05        0 3.25e+08  6.56e+08 atmlayer371 Transportation
    7 4.83e+08 -3.47e+08 6.43e+09     1e+05        0 3.22e+07  6.88e+08  atmosphere Transportation
    8 4.83e+08 -3.47e+08 6.43e+09     1e+05        0        0  6.88e+08 atmlayer370 Transportation
    9 4.92e+08 -3.54e+08 6.43e+09     1e+05        0 1.34e+07  7.01e+08 atmlayer369 Transportation
   10 4.98e+08 -3.58e+08 6.42e+09     1e+05        0 8.11e+06  7.09e+08  atmosphere Transportation
   11 4.98e+08 -3.58e+08 6.42e+09     1e+05        0        0  7.09e+08 atmlayer368 Transportation

Note that the world volume "atmosphere" shows up from time to time.

Any help in getting this to work would be appreciated. Straight down events are good checks of geometry and physics since depth (g/cm2) is known.

Scott Nutter

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1 None: more info: geometry definition   (Scott Nutter - 15 Jan, 2009)
2 None: Re: bug in tracking through concentric spherical layers?   (Vladimir Grichine - 16 Jan, 2009)
1 None: Re: bug in tracking through concentric spherical layers?   (Vladimir Grichine - 16 Jan, 2009)
3 Ok: Re: bug in tracking through concentric spherical layers?   (Scott Nutter - 16 Jan, 2009)
1 None: Re: bug in tracking through concentric spherical layers?   (Vladimir Grichine - 19 Jan, 2009)
2 None: Re: bug in tracking through concentric spherical layers?   (Vladimir Grichine - 23 Jan, 2009)
4 None: Re: bug in tracking through concentric spherical layers?   (Scott Nutter - 27 Jan, 2009)
1 None: Re: bug in tracking through concentric spherical layers?   (Vladimir Grichine - 28 Jan, 2009)
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