[Gate-users] Influence of the system shape?

[Chen, Yu]

Why do you expect the same effect for different geometries?

It seems that the effect you talked about here is mainly scattering if
your crystal size is not very small. 

One can judge it only if you put detailed information here, e.g.,
geometry setup: crystal size (xyz), gap between crystals, distance of source to crystal etc
energy distribution for different crystals in different setups etc.

Yu Chen, Ph.D.
University of Massachusetts Medical School
Division of Nuclear Medicine
55 Lake Avenue North
Worcester, MA 01655-0243
Phone:  (508) 856-6123
Fax:    (508) 856-4572



-----Original Message-----
From: gate-users-bounces at lists.healthgrid.org on behalf of Kiessling, Nicole
Sent: Wed 9/19/2007 5:16 AM
To: gate-users at lists.healthgrid.org
Subject: [Gate-users] Influence of the system shape?
 
Dear Gate-Users,

I found some strange results for the interaction of gamma radiation depending on the scanner system and I cannot find an explanation for it. 
This is what I did:
I want to analyse the cross-talk behaviour of LSO crystals. That's why I have modeled 7 crystals side by side and focused a caesium gamma radiation source only on the crystal in the middle. I have summed up the deposited energy in a special range from a neighbor crystal and set it in ratio with the corresponding energy from the crystal in the middle.
At first I used the sytem "scanner" with the shape "cylinder" defined by Rmax and Rmin. Later I tried to use a box instead of the cylinder. But I get different results using the different shapes and when I change the size of the shapes - even if I use the same random numbers and even if the rest of the scannersystem is defined as vacuum.
I would have expected nearly the same results because I thought that if I use vacuum there would not be any noticeable interaction (before I used air but there were a lot of interactions I did not want to get so I changed it into vacuum).

What can be the reason for this effect?
Which information is predetermined with the predefined system? 
Can anybody help me with this?

I would be very glad about every help.
Thanks in advance.

Kind regards,
Nicole



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