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<p class="MsoNormal">All,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am having a problem with the backtoback helper keyword for pet photons. Perhaps I am doing something wrong you can point out. I have already looked in the user manual and the source code as well.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have a 1cm3 cube source within a large sensitive detector. I define the source like this:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">/gate/source/addSource src_1cmCentered<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/particle gamma<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/setType backtoback<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/monoenergy 511 keV<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/setForcedUnstableFlag true<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/setForcedHalfLife 6586 s<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/setActivity 640000 Bq<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/type Volume<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/shape Para<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/centre 0.000 0.000 0.000 mm<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/halfx 5.000 mm<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/halfy 5.000 mm<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/halfz 5.000 mm<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/angtype iso<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_1cmCentered/gps/confine 1cmCentered_phys<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">When I run this macro, I get approximately 640,000 in _Run.dat. But wait! I thought it would generate two photons for each!<o:p></o:p></p>
<p class="MsoNormal">To test, I deleted the macro line that sets backtoback and reran it. Nothing else changed.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now I still get approximately 640,000 in _Run.dat! <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I compared the hits output from each run and found that with the backtoback flag enabled, I get 55% more hits than I do with it deleted. I would expect 100% more…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any thoughts? What am I doing wrong? I want to make sure that 2 photons are actually being generated for every 1 Bq I enter. The fact that _Run.dat doesn’t change is a small matter if I can be sure the correct number of photons existed.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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