4 ms·

I’ve read about this incident before, what I don’t understand is the parameters of the experiment. What were they trying to learn? Why re-do it multiple times?

I’ve read about this incident before, what I don’t understand is the parameters of the experiment. What were they trying to learn? Why re-do it multiple times? How could this get to the point where this guy was just holding a screwdriver and plopping the beryllium cap onto this core, after a different but similar experiment with beryllium bricks enclosing one of these plutonium cores also killed someone as it started to go critical… doesn’t that prove the point that yes, it will go critical?

Doxin 3y ago
As far as I understand it, it was initially an experiment to determine some figures around when things go critical. Then it turned into a demonstration. Then it turned into a party trick.
mannykannot 3y ago
I have been curious about that as well, as there does not appear to be anything precise about what Slotin was doing. The impression I have from what I have read so far was that he was still in the set-up stage of the experiment, which required an assembly that was close to criticality, and I'm guessing that, once that had been achieved, that actual experiment would be conducted with much greater precision. In this case, he was merely demonstrating the procedure to Alvin Graves, who was to take over Slotin's work, so there may have been no intention of making precise measurements. Raemer Schreiber, who was present in the lab working on something else, wrote "At first Slotin said that he didn't have the proper materials for one. Then he remembered that we had the 49 cores there so he said he would do one 'in about two minutes' in a beryllium tamper after we (Schreiber and Perlman) had finished our counts. I remarked that if he were going to do it in two minutes I was going to leave but would stick around if he took a half hour for it. This was not intended seriously since we all had confidence in Slotin's ability and judgment." In the context of what else I have read about the experiment, I think the "about two minutes" comment referred to how long it would take for Slotin to set up for the experiment. He also wrote "I had assumed that the approach to critical would be rather slow so continued to work on the initiator, thinking that when the multiplication got to an interesting point I would turn and watch." A near- but sub-critical assembly serves as a multiplier (amplifier) of any neutron flux it is exposed to, with the gain asymptotically approaching infinity as the assembly approaches criticality. Again according to Schreiber, Slotin was using a neutron-producing "driving source", and my guess is that setting up for the experiment involved adjusting the assembly until it was producing a sufficiently large multiplication of the driver's neutron flux. As to why this experiment had to be repeated, I get the impression that, at this stage, each bomb was custom-built (or at least the ones for the Bikini tests were), and its fissile core and the surrounding tamper had to be individually calibrated and adjusted. Beyond the description of what Slotin was doing at the time of the accident, I have not seen any description of how the experiment was performed in terms of what measurements were taken, or of its precise purpose. https://www.halflifeofgenius.com/slotin https://www.halflifeofgenius.com/slotin - thanks to toomuchtodo for the reference.
- MarkMarine 3y ago
  Thank you! Answers a nagging question I’ve had for a while.
tnecniv 3y ago
My assumption is that, when you work with this stuff every day, you become desensitized to it and underestimate the risk. When I was a freshman in electrical engineering, I was very careful about disconnecting power. By the time I graduated, me and others in the program would modify live circuits with wonton disregard. The voltages were too low for anything very bad to happen but I do know of at least one laptop that was sent into an emergency power shutdown mode and required some TLC to get it to boot again. You’d like to believe people would be more careful with plutonium cores, but people are lazy and careless.

Doxin 3y ago

As far as I understand it, it was initially an experiment to determine some figures around when things go critical. Then it turned into a demonstration. Then it turned into a party trick.

mannykannot 3y ago

I have been curious about that as well, as there does not appear to be anything precise about what Slotin was doing. The impression I have from what I have read so far was that he was still in the set-up stage of the experiment, which required an assembly that was close to criticality, and I'm guessing that, once that had been achieved, that actual experiment would be conducted with much greater precision. In this case, he was merely demonstrating the procedure to Alvin Graves, who was to take over Slotin's work, so there may have been no intention of making precise measurements. Raemer Schreiber, who was present in the lab working on something else, wrote "At first Slotin said that he didn't have the proper materials for one. Then he remembered that we had the 49 cores there so he said he would do one 'in about two minutes' in a beryllium tamper after we (Schreiber and Perlman) had finished our counts. I remarked that if he were going to do it in two minutes I was going to leave but would stick around if he took a half hour for it. This was not intended seriously since we all had confidence in Slotin's ability and judgment." In the context of what else I have read about the experiment, I think the "about two minutes" comment referred to how long it would take for Slotin to set up for the experiment. He also wrote "I had assumed that the approach to critical would be rather slow so continued to work on the initiator, thinking that when the multiplication got to an interesting point I would turn and watch." A near- but sub-critical assembly serves as a multiplier (amplifier) of any neutron flux it is exposed to, with the gain asymptotically approaching infinity as the assembly approaches criticality. Again according to Schreiber, Slotin was using a neutron-producing "driving source", and my guess is that setting up for the experiment involved adjusting the assembly until it was producing a sufficiently large multiplication of the driver's neutron flux. As to why this experiment had to be repeated, I get the impression that, at this stage, each bomb was custom-built (or at least the ones for the Bikini tests were), and its fissile core and the surrounding tamper had to be individually calibrated and adjusted. Beyond the description of what Slotin was doing at the time of the accident, I have not seen any description of how the experiment was performed in terms of what measurements were taken, or of its precise purpose. https://www.halflifeofgenius.com/slotin https://www.halflifeofgenius.com/slotin - thanks to toomuchtodo for the reference.

MarkMarine 3y ago
Thank you! Answers a nagging question I’ve had for a while.

tnecniv 3y ago

My assumption is that, when you work with this stuff every day, you become desensitized to it and underestimate the risk. When I was a freshman in electrical engineering, I was very careful about disconnecting power. By the time I graduated, me and others in the program would modify live circuits with wonton disregard. The voltages were too low for anything very bad to happen but I do know of at least one laptop that was sent into an emergency power shutdown mode and required some TLC to get it to boot again. You’d like to believe people would be more careful with plutonium cores, but people are lazy and careless.