Since the radiation source is only exposed if it's indicating a potential main rotor crack, and it's not a very strong radiation source in the first place (so it's not like it allows long distance tracking), it seems like a minor risk -- if the radioactive capsule is exposed, the pilot is going to be returning to safe place to land.

Beta particles typically only travel a few meters in air before they lose most of their energy.

Why? It's not like it's gamma radiation.

Wait until you find out about smoke detectors. Or microwave ovens. Or light bulbs. Or anything with nonzero temperature.