Thanks for the message, Paul. <br>
<br>
I noticed that the timing for the lower end of the coincidences has a sharp cut off as one would expect. the problem is with the upper end. So if one were interested in count rates, I wonder what is the right method is to treat the randoms (with timing greater than the coincidence window):<br>
<br>a) ignore them by imposing a sharp cut off in the root analysis file. <br>b) Use all the parameters (detection position, energy etc) but assign a random time to make it fall within the coincidence window. <br><br>I list these obvious steps (a and b ) because it seems the no of events with the 'wrong' time is significant (about 8-9% for the NEMA scatter phantom with 2.2 mCi).<br>
<br>Total Randoms = 362852 <br>Randoms with TOF > 0 = 31539 (the wrong timing ones). <br><br>So is the 'correct' no of randoms (362852-31539) or 362852. <br><br>Thanks.<br>Karthik.<br><br>
<div class="gmail_quote">On Mon, Jun 30, 2008 at 2:15 PM, Paul Vaska <<a href="mailto:vaska@bnl.gov">vaska@bnl.gov</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
We have seen this as well and it seems like a bug. It looks like the coincidence processor is using a different time than the time reported in the output data. For example, if the coincidence code uses the exact event time and the output code reports the event time after time resolution blurring, then you can have events like this. But we've not proven that this is the specific cause.<br>
<br>
Paul<br>
<br>
Paul Vaska, Ph.D.<br>
Medical Department, Building 490<br>
Brookhaven National Laboratory<br>
Upton, NY 11973<br>
<a href="mailto:vaska@bnl.gov" target="_blank">vaska@bnl.gov</a> (631)344-6228 fax:(631)344-4146<div><div></div><div class="Wj3C7c"><br>
<br>
<br>
<br>
On Jun 30, 2008, at 1:45 PM, KB wrote:<br>
<br>
</div></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="Wj3C7c">
Hello all.<br>
<br>
Plotting (time1-time2) for all the randoms coincidences, I notice that the lower value is a sharp cutoff (just as I expect) but the higher value is over and beyond the coincidence window. With my coincidence window set to 6 ns, I see (time1-time2) values as high as 89 ns.<br>
<br>
I have plotted (time1-time2) and uploaded the plot here: http://<a href="http://img337.imageshack.us/img337/4598/gatetalkhm9.gif" target="_blank">img337.imageshack.us/img337/4598/gatetalkhm9.gif</a><br>
<br>
The relevant lines from my digitiser are:<br>
<br>
/gate/digitizer/Coincidences/setWindow 6.0 ns<br>
/gate/digitizer/Coincidences/minSectorDifference 7<br>
/gate/digitizer/Coincidences/MultiplesPolicy takeAllGoods<br>
/gate/digitizer/name delay<br>
/gate/digitizer/insert coincidenceSorter<br>
/gate/digitizer/delay/setWindow 6.0 ns<br>
/gate/digitizer/delay/setOffset 500.0 ns<br>
/gate/digitizer/delay/MultiplesPolicy takeAllGoods<br>
<br>
<br>
I am interested in knowing why I get randoms coincidences beyond the coincidence window. Thanks for any help.<br>
<br>
Karthik.<br></div></div>
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