[gate-users] set the tumor/background activity ratio

[Jin Zhang]

Hello, first thank Long and Corinne for answering my former question. 
Here I got another one to ask.
How to set the tumor/background activity ratio, say to be 5?
I tried to add another source (as background) with 5 times lower 
activity than that of the other tumor sources, and with the same size of 
the whole phantom. However, as my phantom is a half cylinder aligned 
along X axis, I cannot rotate the background source to overlap with the 
whole phantom though.
Is there any better way do this? I checked with the Gate manual, but 
didn't get any useful information yet. So asking here could be much better.
Thanks in advance and have a nice weekend!

Jin Zhang