Bananas are not typically very high on the danger scale except in exotic (and universally embarrassing) circumstances.
In fact, that’s another thing we could use bananas for scale with. Probably driving to work is equivalent to several kilobananas worth of danger daily :)
Anyway, I think the positron should be about 44keV if that helps you calibrate your magnets. The typical banana should produce something on the order of a positron every 10 seconds (although I used much rounding for the sake of brevity). Most commercial positron sources e.g. used in hospital PET scanners, are many times stronger than that!
exotic (and universally embarrassing) circumstances.
As someone who tried to push a banana up their ass in uni - it doesn’t work.