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- RD Program during WWII to produce nuclear weapons
- Responsible for the development of the Fat Man and Little Boy bombs that were dropped on Japan, ending the war in the Pacific
- In addition to the two bombs the US used, there was a third core made of 14lbs of Plutonium named "Rufus."
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- Japan announces its intent to surrender
- Scientists given permission use Rufus, a 3.5" 14lb sphere of plutonium, to test the limits of nuclear material
- Scientists at the Los Alamos National Laboratory begin experimenting with Rufus to better understand the limit between the subcritical and critical state
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- Physicist Harry Daghlian performed an experiment using tungsten carbide bricks to surround Rufus.
- The bricks would act as neutron reflectors, decreasing the subcriticality of the plutonium.
- Physicist Richard Feynman described such experiments as "Tickling the Tail of a Sleeping Dragon."
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- Harry was able to stack the tungsten carbide blocks until his measurements indicated that Rufus was only slightly sub critical
- Realizing that the block he was placing on his reflector shell would be the final straw that pushed Rufus to a critical state, he began moving the block away from the core
- Unfortunately, Harry accidentally dropped the final block and it landed on the core, immediately putting Rufus into a critical state
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- Though Harry quickly removed tungsten to stop the reaction he received an estimated 404rem of neutrons.
- Harry was hospitalized for Acute Radiation Syndrome where he initially had symptoms similar to a bad stomach bug
- His symptoms improved for a few days before rebounding with extreme severity ending in coma and death 25 days after his exposure
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- After Harry's death, Canadian physicist Louis Slotin began conducting similar experiments with Rufus
- His approach involved using two beryllium half spheres as neutron reflectors that he would bring together using a screwdriver to help keep space between them
- He was warned about his approach to critical assemblies by his boss Enrico Fermi who said "You'll be dead within the year if you keep doing that."
- A few months later Louis died because of a second criticality accident involving Rufus
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- 9 months after the Harry's accident, Louis Slotin was giving a tour to Alvin Graves, the scientist would be replacing him
- Alvin saw the critical assembly (Rufus) and commented that he had never seen it demonstrated before
- While demonstrating the experiment, the screwdriver slipped and the two reflectors fell together, completely enclosing the plutonium and causing a prompt criticality event
- Knowing he had received a lethal dose of radiation, Louis simply said, "Well, that does it."
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- Pu239 emits neutrons as it decays. These are called delayed neutrons. Occasionally, these neutrons will strike other Pu239 atoms, causing them to split and emit even more neutrons, known as prompt neutrons
- Pu239 is said to be critical when there are enough neutrons to sustain a chain reaction of atomic fissions
- Prompt criticality is when there are sufficient prompt neutrons to sustain the chain reaction without the need for the delayed neutrons. This leads to an out of control reaction
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- After the incident with Louis Slotin, Rufus began to develop a sinister reputation. Not only had the core killed two people, but the similarities between the two were too much to be ignored.
- Daghlian's accident occurred on Tuesday the 21st. The next Tuesday the 21st that year was exactly 9 months later and happened to be the day of Slotin's unfortunate accident.
- Slotin also received medical treatment and eventually died in the exact same hospital room that Daghlian died in months before.
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- The tragic deaths of Daghlian and Slotin sparked a change in the nuclear industry as new safety procedures were implemented and workers developed a safety culture.
- Hands-on criticality experiments were effectively banned. Remote operation of robots and use of shielding are now standard
- Computers are used to simulate experiments before they are performed
- Double contingency: systems were safe unless two independent things failed at once
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You can invent all the tools you want, but the single most important change was people agreeing not to re-glorify risky behavior. That cultural shift — from ‘‘brave tinkerer’’ to ‘‘procedural scientist’’ — probably saved more lives than any single gadget.