The story so far...
Carbon 14 would be a good explanation for the detected radiation except for (as pointed out by Ryan), it is a weak emitter of beta below the threshold of the detectors.
But according to - https://en.wikipedia.org/wiki/Carbon-14
it can be detected if volumes are high enough. The G-M detectors probably operating at 3% efficiency.
If there was a lot of C14 there it could be an explanation for the tests.
So i hear you thinking, how does a peak in the Urals get much higher than normal levels of C14?
Because if a proportion of atmospheric C14 is ionised (somehow) and the peak has the reverse charge then it will collect.
Back to electro magnetism?