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Forum: Event and Track Management
Re: Question Question re stopping power of lead (Neil Fazel)
Re: Feedback Re: Question re stopping power of lead (Neil Fazel)
Date: 11 Sep, 2011
From: Robert Penny <Robert Penny>

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Hi Neil,

For what it's worth, as the gamma energy goes above 1.1 MeV, pair =
production starts to kick in as a gamma absorption mechanism.  This is =
more apparent in high-Z materials like lead.  This may be what you're =
seeing.  Not quite sure if you'll actually get a turning point with =
increasing energy, but it will certainly flatten out the increase in =
penetration with energy in this regime.

You can always do a quick and dirty independent estimate of stopping =
power for gammas as a function of energy using the NIST XCOM photon =
database.

http://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html

-Rob.


-----Original Message-----
From: douglas@slac.stanford.edu on behalf of Neil Fazel
Sent: Sat 9/10/2011 4:44 PM
To: eventtrackmanage-g4hn@slac.stanford.edu
Subject: Re: Question re stopping power of lead
=20

*** Discussion title: Event and Track Management

I found out the problem. I had omitted /gun/particle e- from my macro
and it was using the program's default particle. Since I had used ExN03
to build my program, the default particle was a gamma not electron. For
some reason, the absorption of gammas in lead increases with increasing
energy.

Neil

-------------------------------------------------------------
Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or =
unsubscribe) at:=20
http://hypernews.slac.stanford.edu/HyperNews/geant4/get/eventtrackmanage/=
1026/1.html=20


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<P><FONT SIZE=3D2>Hi Neil,<BR>
<BR>
For what it's worth, as the gamma energy goes above 1.1 MeV, pair =
production starts to kick in as a gamma absorption mechanism.&nbsp; This =
is more apparent in high-Z materials like lead.&nbsp; This may be what =
you're seeing.&nbsp; Not quite sure if you'll actually get a turning =
point with increasing energy, but it will certainly flatten out the =
increase in penetration with energy in this regime.<BR>
<BR>
You can always do a quick and dirty independent estimate of stopping =
power for gammas as a function of energy using the NIST XCOM photon =
database.<BR>
<BR>
<A =
HREF=3D"http://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html">http://=
physics.nist.gov/PhysRefData/Xcom/html/xcom1.html</A><BR>
<BR>
-Rob.<BR>
<BR>
<BR>
-----Original Message-----<BR>
From: douglas@slac.stanford.edu on behalf of Neil Fazel<BR>
Sent: Sat 9/10/2011 4:44 PM<BR>
To: eventtrackmanage-g4hn@slac.stanford.edu<BR>
Subject: Re: Question re stopping power of lead<BR>
<BR>
<BR>
*** Discussion title: Event and Track Management<BR>
<BR>
I found out the problem. I had omitted /gun/particle e- from my =
macro<BR>
and it was using the program's default particle. Since I had used =
ExN03<BR>
to build my program, the default particle was a gamma not electron. =
For<BR>
some reason, the absorption of gammas in lead increases with =
increasing<BR>
energy.<BR>
<BR>
Neil<BR>
<BR>
-------------------------------------------------------------<BR>
Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or =
unsubscribe) at:<BR>
<A =
HREF=3D"http://hypernews.slac.stanford.edu/HyperNews/geant4/get/eventtrac=
kmanage/1026/1.html">http://hypernews.slac.stanford.edu/HyperNews/geant4/=
get/eventtrackmanage/1026/1.html</A><BR>
<BR>
</FONT>
</P>

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