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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hi Ashley.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>That happens when you have positron escaping your
phantom without any interaction and when it happens too often. The clean solution
is to put a medium around your phantom and a<st1:PersonName w:st="on">tt</st1:PersonName>achSD
to it. At first I would a<st1:PersonName w:st="on">tt</st1:PersonName>achSD to
air (default) of world object. If your world dimensions are too small to stop
positrons, add more dimension to it. Then there are dirty solutions: (i) run
a simulation on a slower computer – I had run the same simulation on two
different machines with same gate and geant4, lower speed healed the problem, (ii)
add a shell of water or plastic around your phantom if you may, (iii) add
remote lead box around your system and a<st1:PersonName w:st="on">tt</st1:PersonName>achSD
to it.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>To check the problem, try to see the histogram
Positron_anihilation_distance_mm in the top structure of root file (above
singles and coincidences) – run: “root filename.root” and
then “TBrowser t” from the prompt. It will tell you how far your
positrons passed from creation. But for that you need a clean closed root file,
so first overdo the positron shielding.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>I hope that helps <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoAutoSig><st1:PersonName ProductID="Marcin Balcerzyk" w:st="on"><st1:PersonName
w:st="on"><font size=2 face=Verdana><span lang=ES-TRAD style='font-size:10.0pt;
font-family:Verdana'>Marcin</span></font></st1:PersonName><font size=2
face=Verdana><span lang=ES-TRAD style='font-size:10.0pt;font-family:Verdana'>
Balcerzyk</span></font></st1:PersonName><span lang=ES-TRAD><o:p></o:p></span></p>
<p class=MsoAutoSig><font size=2 face=Verdana><span lang=ES-TRAD
style='font-size:10.0pt;font-family:Verdana'>Univesrsitad Complutense de Madrid<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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