If there's anything to pick on this picture, the 'blue light' is a sign of the Core going supercritical, and it blasting enough radiation. At such, you shouldn't be able to see the light unless you're there, in person, because it's actually Cherenkov's Radiation that happens in your eyeball.
That's the real life object called the demon core. In short, when the top half drops down on the bottom half a metric fuckton of radiation gets released.
To give a more detailed explanation, itās a subcritical core of plutonium that was originally going to be used in a nuclear bomb. In fact, it couldāve been the third nuclear bomb to drop on Japan if they hadnāt surrendered. However, they didnāt know whether or not the core was close to criticality, so being the scientists that they were, they decided to fuck around and find out. Now, the problem with Rufus (that was his original nickname) was that there was a VERY fine line between Rufus entering delayed criticality (which is easily controllable) or prompt criticality (a sudden, uncontrollable blast of nuclear energy). This latter fact would be demonstrated to great (and terrible) effect in the two experiments aimed to prove Rufusā criticality.
The first incident involved Harry Daghlian placing tungsten carbide bricks around Rufus, in order to measure the readings off of the neutrons being reflected. He then accidentally dropped one of the bricks on top of Rufus, it entered prompt criticality, and Harry was hit with 200 rads of neutrons and 110 rads of gamma rays. He died 25 days later from acute radiation syndrome.
The second incident, however, truly earned Rufus the title of the āDemon Coreā. Louis Slotin and seven other colleagues used the same neutron reflection method in order to measure how close it was to criticality, but this time they used two half-spheres composed of beryllium instead of bricks, with manually lifting and lowering the top half via a thumb hole at the top in order to modulate the neutron multiplication rate. However, shims were needed to keep the halves separated, as if they were allowed to close completely, the neutrons would be trapped and Rufus would go into prompt criticality. They did not use shims or the thumb hole. Instead, Louis used a flathead screwdriver to fulfil both functions, allowing the two halves to rest on one side for 180Ā° and twisting the head around to change the distance between them. Slotin was so enraptured with his own (incredibly dangerous) method, that he took to showing it to others, usually in his stereotypical cowboy attire. On May 21st, 1946, as Slotin was lowering the top half, the screwdriver slipped by a fraction of an inch, enclosing Rufus completely. Rufus hit critical, and a blue flash of radiation and heat hit Slotin. In half a second, Louis flopped the top half off, which, aided by the initial heat, prevented more radiation from coming out and ceasing Rufusā critical state. Unfortunately, the damage was done. He was hit by 1000 rads of neutrons and 114 rads of gamma rays. Slotin died nine days later. However, thanks to his quick thinking and absorbing most of the rays, the other researchers survived the ordeal.
On one hand, the deaths were both horrible, tragic accidents, caused by the hair trigger nature or hands-on criticality testing, with the latter being a gross example of negligence. On the other hand, it gave medical researchers unprecedented and never before seen data on how radiation dosing works in the human body, from several subjects placed at different ranges to the different effects of varying levels of radiation.