I read a bit on radiation and criticality, so I have some familiarity with that. I was reading about the details of the criticality accident. From what I understand, he was trying to place a neutron reflector on top of the demon core, and kept it apart only with a screwdriver wedged between the two reflector halves. The screwdriver slipped, the reflector made contact with the core, and radiation was released.
My question is, was it the physical contact of the reflector that caused the radiation to be released? How? From what I understand, reflectors speed up fission kind of how a potato cooks faster when wrapped in foil. Is it really all that it takes to cause nuclear fission, and not some elaborate bomb or reactor mechanism?
In: Physics
Nuclear fission is caused by neutrons breaking apart uranium and/or plutonium atoms — creating atoms of lighter elements and generating a couple more neutrons in the process.
The key to a nuclear chain reaction is convincing those two neutrons to break apart another atom each, which release another two neutrons, and on it goes.
When this happens, the mass has gone ‘critical.’
When you have a ball of subcritical plutonium, most of the neutrons just end up flying out into space. When you introduce a neutron reflector, those neutrons bounce back into the mass to cause more fission.
In a nuclear reactor fission is managed by retractable neutron-absorbing control rods that keep the reaction from racing out of control.
When Slotin’s reflector slipped and fell on the plutonium pit, the reaction raced out of control and showered the surrounding area with neutrons. If the reflector hadn’t been removed, the pit probably would have heated to the point of melting.
An atomic bomb is little more than a bunch of high explosives that crush a subcritical mass into a supercritical mass — the plutonium (or uranium) atoms are shoved so close together the nuclear chain reaction builds exponentially to the point where the energy is explosively released in a matter of microseconds.
The amazing thing about such short timescales is that weapons designers add things like heavy metal tampers designed to contain the exploding reaction for just a few millionths of a second — long enough to get one or two extra neutron generations in and amplify the explosion by several orders of magnitude.
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