Comment by no-s

I had a loaner machine (RS-6000 minicomputer) that would have unrecoverable ECC errors when the cover was on. The tech would come and try to diagnose it, but with the cover off, everything would work fine. He'd swap the memory anyway and put the cover back on. within a few hours the memory bank would be failing again. Turned out the machine had been a loaner in a lab where it had acquired some alpha-emitting goo on the inside of the side panel. The lab had just run it with the side panel off to solve the problem, never noticing the goo, never mentioning it to IBM when they packed it up to ship.

It's a long story but the gist is after multiple board swaps, realizing we'd isolated the panel as the fault, I noticed the goo and on a hunch checked it with a scintillator, deducing it was alpha when cardboard blocked it. Turns out the ultra-precious-metal IBM heat sink on the board had an open path that effectively channeled the alpha particles into one of those multi-chip carrier thingies, which featured exposed chips.

As for why I had a scintillator lounging in my desk at a portfolio management company, don't ask. Let's just note the iconic IT anti-hero of that era was the Bastard Operator From Hell, and leave it at that.