Because a couple of theories predict 14C (Fisher, Bazhutov) when natural carbon is present. Secondly betas without gammas are observed. Of course it might be something else too. Do you have suggestions?
I see. That makes sense. I take it your point about betas without gammas is that there are no excited levels that are populated after the beta decay? If the daughters are light elements, I suppose any excited levels might be very low-lying.
My own initial thought: short-lived unstable decay daughters from the breakup of small amounts of U, Th, Ag, Cd and Pb which might be present in the anthracite, and perhaps breakup of nuclides in the electrode material, whatever that is.