Problem 1425 - magnetic field and multiple scattering
Summary: magnetic field and multiple scattering
Status: RESOLVED WONTFIX
Alias: None
Product: Geant4
Classification: Unclassified
Component: processes/transportation (show other problems)
Version: other
Hardware: All All
: P5 trivial
Assignee: John Apostolakis
URL:
Depends on:
Blocks:
 
Reported: 2013-01-14 19:01 CET by michel.maire
Modified: 2013-04-03 16:42 CEST (History)
0 users

See Also:

Attachments
picture of 20 events (5.79 KB, image/png)
2013-01-14 19:01 CET, michel.maire 		Details
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Description michel.maire 2013-01-14 19:01:17 CET 
Created attachment 200 [details]
picture of 20 events

G4Transportation saves smooth trajectory AlongStep before multiple scattering is invoked. In novice/N03, with the following commands, we see the attached picture.

 #this macro can be executed at any time during an interactive session:
 #
 # Idle> /control/execute magfield.mac 
 #
 /N03/det/setNbOfLayers 1
 /N03/det/setAbsMat Water
 /N03/det/setAbsThick 40 cm
 /N03/det/setGapMat Air
 /N03/det/setGapThick  0 cm
 /N03/det/setSizeYZ   40 cm
 #
 /N03/det/setField -5 tesla
 #
 /N03/det/update
 #
 /vis/viewer/zoom 1.3
 #
 /gun/particle proton
 /gun/energy 500 MeV
 #
 /run/setCut 1 km
 #
 /run/beamOn 20
Comment 1 John Apostolakis 2013-04-03 16:42:03 CEST 
Saving the smooth trajectory before the displacement was seen as a desired feature when we created it. It allows a user to identify the discreteness of the stepping - what process causes a deflection or displacement.

It is also the way in which Geant4 works - we store the intermediate points as calculated by integrating with the field and then apply the deflection and displacement at the endpoint.

In addition, the energy loss is not taken into account during the integration in the magnetic field - so getting a very accurate picture anyway requires having smaller steps.

If this is not the issue, could you please explain what you believe the problem is ?