I had no idea they were that detectable.

In HS in the late '50s I was the student lab assistant in a university soil physics laboratory. We had a neutron source sitting in a bucket of lead in the corner. After several months a grad student measured what was coming outside the lead. Not good, I don't remember the numbers, but it was immediately taken away by faculty members wearing lead.

Some time later I was sent to Eastern Oregon to pick up a neutron sample being used in soil moisture measurement. Ostensibly not trusting the shielding, I picked it up, put it into the trunk, and then pulled into a roadside stand and loaded watermelons into the trunk and back seat. A lot of watermelons, the suspension was seriously strained. I made sure to get a receipt.

After getting back to campus after hours, I unloaded the sample, piled watermelons in the office with the receipt, and lab, and gave watermelons away to everyone I knew.

I thought I was pretty clever. And sorta still do.