[gate-users] Energy Spectrum Woes - Dual Head and 4 Head Designs & Number of Heads

Wed Sep 15 19:14:02 CEST 2004

Hi, Angela Foudray,

I checked your files and I think you don't need to worry to much about the 
energy spectrum problem.
We know that there are two singles in each coincidence data, let's call 
them s0 and s1. When Gate output
the coincidences data, the program should have some algorithm which 
decides which one should be 
output first and which one should be the second. We don't know what's that 
algorithm is, but we are
sure it's not based on the index of the rsector. In this case we can not 
say that s0 and s1 should
have the same distribution function. So the difference of the two energy 
spectrum plot from
the output coincidences file doesn't mean anything to us. What is 
meaningful for us is that the spectrum
of each sector (or module, crystal,...) should be the same. You can do the 
statistics of the spectrum
of the two sectors by yourself from the ASCII coincidence data, and you 
will see the two spectrum are
indeed identical.

You can check these four spectrum. Figures of coincidences1.gif and 
coincidences2.gif are plot with the 
coincidences data. Sector1 and 2 are plot according to the sector number.

Yuxuan Zhang

Dr. Yuxuan ZHANG 
Dept. Experimental Diagnostic Imaging
Univ. Texas, MD Anderson Cancer Center
1515 Holcombe Blvd, Unit 217
Houston, TX 77030-4095

Tel: +1-713-745-1671 
Fax: +1-713-745-1672

Angela M K Foudray <afoudray at stanford.edu>
Sent by: gate-users-bounces at lphe1pet1.epfl.ch
09/02/2004 02:58 PM
Please respond to GATE feedback and helpline for Users

        To:     GATE feedback and helpline for Users <gate-users at lphe1pet1.epfl.ch>
        cc: 
        Subject:        [gate-users]    Energy Spectrum Woes - Dual Head and 4 Head Designs & 
Number of       Heads

I forgot to mention why I used the subject I did for the last post - the 
energy spectrum problems at the 
high energy (700 keV) that I mentioned is most apparent in the dual head 
design, goes slightly away in 
the 4 head design, and is not apparent at all in a ring design of 20+ 
"heads".  In other words, the severity 
of this anomalous high energy peak seems to be a function of the number of 
heads in the system.  (In case 
you're wondering, we have /gate/digitizer/Coincidences/minSectorDifference 
1)

I'm attaching spectra (lower counts than the previous spectra I sent) for 
4,5,6 heads and a ring design.
I'll also send you the .mac file for the dual head ("dhci_sen10cm.mac").

You'll notice, even for the ring, the spectra are not similar in the low 
energy region ("sasens_ring_np60_oe.mac")...

Ange
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