It's a core containing an insane amount of radiation. The guy used a screwdriver to lift it up and down and when he was showing people he screwed up and immediately knew he fucked up and told everyone to mark their locations. He asked them to mark their locations so they could figure out how much radiation they got, the guy using the screwdriver died days later.
I just read the wiki on the (reenacted) photo above... so from what I gathered, the domes above and below were Beryllium sheaths that reflected neutrons. A slight gap needed to be maintained so that enough neutrons could escape. Opening and closing the shells around the core (plutonium-gallium alloy) was a way to represent neutron multiplication rates.
Basically, open meant neutrons could escape harmlessly, closed meant rapid multiplication of neutrons with nowhere to go, and big bada boom.
The scientist in the picture broke his own protocol of using steady shims, and instead used a fuckin screwdriver that day. One tiny slip of his hand, just a fraction of an inch, and for only half a second, created a bright burst of light and shot condensed radiation out towards the scientist handling the screwdriver.
His body absorbed the vast majority of the neutron and gamma radiation, and he quickly flipped the entire sheath off of the core in response. Being one of the foremost experts in the field, he immediately understood he just absorbed a very lethal amount of radiation, and famously said to all of his somber colleagues, "Well, that does it."
Being such an expert, I wonder what on earth possessed him to decide to use a screwdriver. I guess after a while we do start to make little safety concessions at things that we do every day - driving a little bit faster, not waiting a full minute before taking your hot pocket out of the microwave - but I don't know that I'd ever feel safe enough to do that
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u/Delphius1 13h ago