I recall reading about that event in the excellent book “Surely You’re Joking, Mr. Feynman!”
They had a shielded sphere, and they would use two screw drivers to pry the top half away, and could measure the increase in neutron production (I recall because the further away the top part got, the fewer neutrons were being absorbed, and you could measure the activity going up on a detector.
It was fun and games (with a very, very small amount of learning, but mostly the guy was doing it for jollies) and remained fun and games until one day he pried it up, and the top shifted off the screwdrivers, and they had a critical event.
Boom. It was only for a few seconds, but the daamage was done. What an awful way to die.
i’ll say! a whole life ahead of him, why do that? But why do people jump out of planes and drive race cars, and eat 20 buffalo wings at a time, er, that last one wsan’t about me!!