[Gate-users] Re: 100KeV peak

[Maria Holstensson]

Hi Park MinJae,

The peak at 100 keV could be your backscatter peak.
Gamma rays that have been compton scattered in one
of the materials around the detector and redirected back
at an angle of ~180 degrees will have an energy of hv', which
can be calculated:

hv' = hv / (1 + 2*hv/m0c^2)

where hv is the energy of the primary gamma ray (140.5 keV),
and m0c^2 is 511 keV. In the case of 99mTc this will result
in a backscatter peak at around 91 keV. When the scattering
angle is less, the energy of the scattered photon is higher.


I hope this helps,
Maria





>>> gate-users-request at lists.healthgrid.org 13/03/2008 11:00 >>>
----------------------------------------------------------------------

>Message: 1
>Date: Thu, 13 Mar 2008 16:20:42 +0900
>From: "Park MinJae" <MJ at ToTi.us>
>Subject: [Gate-users] ROOT file merge...
>To: <gate-users at lists.healthgrid.org>
>Message-ID: <000001c884da$bef7d8b0$2335dbd2 at mjnm2>
>Content-Type: text/plain;	charset="us-ascii"


>Dear GATErs,

>moreover, I tried to validate the energy spectrum shape of Tc-99m

>
http://ftp.toti.us/gate/root_merging/energy_spectrum_compare_root_merged_by_

> filemerger_and_experiment.jpg
>there is a peak at 100KeV at energy shape of experiment ...but I
can't
>figure it out...

>
http://ftp.toti.us/gate/root_merging/energy_spectrum_compare_root_merged_by_

>script_and_experiment.jpg
>however, there is more peaks at under 10KeV, 30KeV, 110KeV...

>I guess 100KeV peak might be from superposition of 90KeV and
110KeV...
>90KeV is characteristic x-ray from NaI crystal...
>110KeV is characteristic x-ray from lead shielding...
>however, the probability is quite low...

>any idea about 100KeV peak?

>thanks,
>MJ



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