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Question Synchrotron radiation path length cutoff? 

Keywords: synchrotron radiation path length cutoff
Forum: Physics List
Date: 04 Jan, 2007
From: Scott Nutter <Scott Nutter>

Hi -

I have been looking at the output of 
examples/extended/electromagnetic/TestEm16, which explores synchrotron radiation.
My application is in the atmosphere, so I am looking at very long distances (>100 km), 
high energies (>10 TeV), and low field strength (B_perp = 0.5 gauss). 

A histogram of the path length is created, and a statistic is printed out about it as well.
I extended the size of the histogram to look at path lengths beyond 1 km, but
to my surprise none were present.  There is a cutoff at 1 km.  For a 10 TeV 
electron in a field of 0.5 gauss, the mean free path is calculated to be 3.3 km.
However, statistics printout at the end of each event says ~500 m, which is 
expected for a flat distribution cut off at 1 km.

Why the cutoff at 1 km in path length?

Here is an input file which can be used with TestEm16 to see this cutoff. You must
modify the histogram upper ends to be on scale.

# $Id:,v 1.3 2006/05/24 12:58:49 maire Exp $
# Macro file for ""
# (can be run in batch, without graphic)
/control/verbose 2
/run/verbose 2
# inactivate other processes to make SynchrotronRadiation more visible
/process/inactivate msc
/process/inactivate eIoni
/process/inactivate eBrem
/process/inactivate annihil
/process/inactivate phot
/process/inactivate compt
/process/inactivate conv
/gun/particle e-
/gun/energy 10000 GeV
/testem/det/setSize 200 km
/testem/det/setMat Vacuum
/testem/det/setField 0.5 gauss
/run/beamOn 2000

Scott Nutter
Northern Kentucky University

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