[Gate-users] Interaction depth and attenuation coefficient

[Rajaram, Ramya (H USA)]

Hello Gaters,
 
I am trying to simulate a NaI crystal, with no collimator (nothing at
all in the SPECThead except the crystal) to find out the mean
interaction depth in the crystal and the attenuation coefficient from
the log plot of counts versus depth into the crystal.
The attached file has the macro and the output/analysis. From the
Singles tree in ROOT, the variable "globalposZ" was plotted. As one can
see in the attachment, this plot always shows a sudden drop in the
counts at a certain depth into the crystal with the drop being worse
when crystal thickness is reduced. As a result, all data points can't be
used to estimate the attenuation coefficient. Also, even if only the
linear portion of the graph is used, the value of the attenuation
coefficient is much less than what NIST says it should be for NaI at 140
keV.
What could be wrong - can somebody help me? I really appreciate any
comments/suggestions.
 
Thank you,
 
Ramya
 

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