A concern for securing the homeland is screening of incoming
containers for radio active materials.
A number of false positives are given by banana shipments,
due to the natural beta emissions from the 40K Potassium
constituent of bananas.
I set out to make a quick check of the visibility of such
sources.
I took a GoWalking step counter by Proline inc (< $5) and
wired two slender wires from the contacts which short by
pendulum action during walking/running exercise.
I connected them across the survey meter connector which
normally takes the audio click to the headphone.
This provided a plus one count for each jump of the analog
meter, and I judged it was counting essentially all the
separate pulses.
I placed the unshielded Geiger tube in a bunch of bananas,
where the counter added 108 in 15 minutes, then with the
tube pointing into room air I saw the count increase by 147
in 20 minutes. I concluded that these 1.32 MeV betas were
not in range of my detection.