Again I have to mention that the pancake detector is really sensitive for this kind of radiation. BUT the radiation source must be really close. It looks that the particles are annihilated by anything metallic. But putting any metal at the paper will actually not change the counts (from other side than what is measured) - counts are still clearly elevated.
On the other hand I have tried other tests to exclude some static electricity charging by grounding surface of the paper. And grounding is not affecting it at all.
Moreover my Pancake detector is powered by Ludlums survey metter - from batteries. I like this survey meter a lot because it is really immune to any kind of RF.
Great thing about the Pancake detector is that you can really see discharges so there is no doubt about radiation presence.