They were “tickling the tail of the dragon”, bringing two slightly sub critical masses close together to calibrate the reaction rate. The top piece slipped and landed on IN CONTACT WITH the bottom piece. This produced a spike of radiation so intense there was a brilliant flash of blue ÄŒerenkov radiation. In effect it became a nuclear reactor at full power, with no shielding, the scientist grabbed the top piece and removed it, stopping the reaction in its tracks.
I would love to know what this means. It is hard to grasp. And harder for knowledgeable people like yourself to break down into idiot terms for people like me lol The scary part is you probably think you’ve already broken it down into idiot terms lol. What does that say about me!!
http://en.wikipedia.org/wiki/Demon_core
First incident
On August 21, 1945, the plutonium core produced a burst of neutron radiation that led to Harry Daghlian’s death. Daghlian, a physicist, made a mistake while working alone performing neutron reflection experiments on the core. The core was placed within a stack of neutron-reflective tungsten carbide bricks and the addition of each brick moved the assembly closer to criticality. While attempting to stack another brick around the assembly, Daghlian accidentally dropped it onto the core and thereby caused the core to go critical, a self-sustaining prompt critical chain reaction. Despite quick action in moving the brick off the assembly, Daghlian received a fatal dose of radiation. He died 25 days later from acute radiation poisoning.
Second incident
On May 21, 1946, physicist Louis Slotin and seven other Los Alamos personnel were in a Los Alamos laboratory conducting an experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. The test was known as “tickling the dragon’s tail” for its extreme risk.
...Under Slotin’s unapproved protocol, the only thing preventing this was the blade of a standard flathead screwdriver, manipulated by the scientist’s other hand. Slotin, who was given to bravado, became the local expert, performing the test almost a dozen separate times, often in his trademark bluejeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be “dead within a year” if they continued performing it.
On the day of the accident, Slotin’s screwdriver slipped outward a fraction of an inch while lowering the top reflector, allowing the reflector to fall into place around the core. Instantly there was a flash of blue light and a wave of heat across Slotin’s skin; the core had become supercritical, releasing an intense burst of neutron radiation estimated to have lasted about a half second. He quickly flipped the top shell to the floor. The heating of the core and shells stopped the criticality within seconds of its initiation, but Slotin’s reaction prevented a recurrence and ended the accident. Slotin’s body’s positioning over the apparatus also shielded the others from much of the neutron radiation. He received a lethal dose of 1000 rads neutron/114 rads gamma in under a second and died nine days later from acute radiation poisoning.
Need to get to work, will address this later. (If I get distracted and forget -not unlikely! Feel free to remind me).
Ok, let me take a swing at clearing a couple things up. A subcritical mass means there isn’t enough radioactive material in one “lump” to initiate a nuclear reaction. It is still radioactive, because the isotopes are always decaying and giving off radiation, but there is no chance that it will start a reaction giving off massive amounts of radiation.
A critical mass happens when enough of the material is in one “lump” for a nuclear reaction to begin. Once that happens, you get nuclear fission, meaning the isotopes are not just decaying, steadily giving off “rays” of radiation over time, they are actually splitting apart at the molecular level, releasing huge quantities of energy and radiation every time that happens, and it will continue to happen in a chain reaction until all the fissile material is broken down into less reactive substances.
The raw amount of material is not the only factor, it also has to be in the right state and a proper shape for a chain reaction to start, but since they were building a nuclear bomb, the material they were working with was already in that configuration. All that was needed for a fission reaction to start was for the two masses to come into contact.
Go to the link below, from the Movie "Fat Man Little Boy". I don't know how accurate the movie was, but you will get the idea of the pieces coming in contact with one another....