4 ms·

Despite it being so famous, and the memes, I still don't understand what Slotin was doing. So I get it, it was a demonstration of how to perform an experiment.

Despite it being so famous, and the memes, I still don't understand what Slotin was doing. So I get it, it was a demonstration of how to perform an experiment. But I can't understand how the screwdriver makes any sense at all. What's being measured? What does success and failure look like? What does the experiment produce, what data in what format? Because in my head, a proper experiment has data collection and precise measurements. Somebody's working on a data table that says "At position X, we measured value Y". But randomly wiggling stuff around with a screwdriver, I can't see how one can do anything of the sort. And I figure at this level, "more coverage = more radiation" is kind of a trivial point that doesn't really need to be demonstrated.

sho_hn 2y ago
My understanding is that he was demonstrating a technique for how to bring the system to near supercriticality, without causing it. I.e. the objective was to look at the measurement devices they had and monitor them, and build an understanding of what the data was showing. This would then (in principle) be repeated by others with more specific objectives later. Obviously they should've built a rig for that (at least), but I guess there was a "ain't nobody got time for that" attitude.
- dale_glass 2y ago
  Right, but shouldn't distance be a critical part of such a measurement? Like if we measure the amount of noise a device makes, we do it in a quiet room and at a standard distance. Without precision there's no useful data being generated. So that's the part that I don't get. Shouldn't there be a screw being turned precise amounts, precisely made shims, or at least calipers be involved?
  - sho_hn 2y ago
    I think it was more about being able to understand/read what the measurement devices were showing. The exact distance probably wasn't as important as the criticality could also vary with other variables (e.g. geometry). As in, you're trying to understand the situation as "shouldn't they have precisely nailed down all the parameters, if the goal is to measure when X starts happening". But it seems Slotin was more demonstrating "this is what you're going to see on the monitors when stuff is close to going boom". It wasn't about "this specific distance is a safe gap" and more "here's how you can tell whether the gap is safe". He was about to be reassigned out of the lab, and was demonstrating equipment to his designated successors.
  - davisp 2y ago
    Sometimes science doesn’t have to be precise to demonstrate a result. Consider trying to measure feedback from a microphone and speaker. You don’t have to be an expert to know that there’s a quick change in system behavior when the microphone gets too close to the speaker.
  - StableAlkyne 2y ago
    The honest truth is there's just a certain acceptable level of jank in a scientific lab. Not everything needs to be measured to a high precision to be useful, and it's always a balance of how much effort you want to expend versus how useful that extra accuracy/precision is. If all you care about is "when you're getting close to a critical mass, your instruments will look like this," you don't care that you have a wide swing in your data. You just want to show a difference from baseline.
  - stetrain 2y ago
    If the goal is to collect precise data and use it after the experiment to draw conclusions, update a model, etc. then sure. If the goal is to demonstrate to observers how the neutron output (reaction rate) increases as the reflectors are moved closer together over the source, then that isn't really necessary. This seems more like an incredibly dangerous version of a demonstration you might see at an interactive science museum or a classroom. You don't need precise measurements to demonstrate the relationship between two phenomenon.
  - rocqua 2y ago
    This is just proving 'move spheres closer means more neutrons'. It's something you quickly show someone to explain what you are going to do. The people watching will then get most of the same ideas you are suggesting, and figure out how to design a proper experiment around it. Presumably the experiment to be done later is about characterizing different cores. They had already done it for this core, and wanted to teach the principles to others.
lm28469 2y ago
It's all in the wiki: https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core > It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core using a thumb hole at the polar point. As the reflectors were manually moved closer and farther away from each other, neutron detectors indicated the core's neutron multiplication rate. The experimenter needed to maintain a slight separation between the reflector halves to allow enough neutrons to escape from the core in order to stay below criticality. The standard protocol was to use shims between the halves, as allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion. > Because in my head, a proper experiment has data collection and precise measurements. In your head yes, in early nuclear science it seems protocols weren't that important as long as it went boom in the end. As with many industries, regulations are written in blood
- dale_glass 2y ago
  I've read that and it doesn't really answer those questions. How can you measure the core's neutron multiplication rate if you're not exactly controlling the distance? Isn't the measurement going to be all over the place?
  - kstrauser 2y ago
    In a demonstration, not an experiment, it’s sufficient to have the Geiger counter go clicky at different rates while the demonstrator plays the sphere like a theremin. The point was to show it to people, not to collect data.
    - eichin 2y ago
      > plays the sphere like a theremin Wow, that's a brilliantly horrifying image. (Are there other analogous ones? Does anyone do musical timing of building demolitions, or something like that?)
      - 2y ago
deleted 2y ago
[deleted]
Grimblewald 2y ago
The problem with this image of science is that in order to properly collect things we have to properly understand things we could be collecting. We can certainly do our best, but sometimes unexpected things happen. Take x-rays and their incidental discovery via the effect of x-rays on nearby photo-film. Totally accidental data collection from work at the bleeding edge, which was work that has transformed society as we know it. Another point is that in order for things like the lab equipment to be sleek and well built, we need to understand needs. This means that any research that meets your criteria is quite likely not at the cutting edge of anything. Most cutting edge labs I know look more like someone raided the hardware/electronics store to build some abomination than the Hollywood sleek and shiny labs you might be picturing. The sleek well built shiny labs you are picturing tend to be corporate labs and the like, doing work on safe and predictable things with well defined scopes. Translating existing knowledge into marketable products is a lot easier than discovering genuinely new knowledge.
- dale_glass 2y ago
  This was after Hiroshima and Nagasaki, in a secret, government lab staffed by the utmost experts. It wasn't the "oh look, something funny happens if I do this!" stage of experimentation. This was after they understood what they were dealing with well enough to build and successfully use two bombs. And Slotin was supposedly about to move elsewhere and was working on passing on knowledge. That's why it's so weird to me.
  - Grimblewald 2y ago
    Experimentation is _ALWAYS_ at the "oh look, something funny happens if i do this" stage, otherwise it isn't experimentation/research but rather research/development. If we know what to expect, why experiment? Why waste resources?
Aardwolf 2y ago
Put a half-sphere reflective shield around a nuclear substance which will make the substance more reactive due to neutron reflections. Due to a slip-up with the screwdriver that was supposed to hold it up, accidentally fully drop down the shield, causing the too large radioactive reaction I think with his reaction afterwards to remove it again, he saved the others in the room, but not himself
alt187 2y ago
Nothing. Richad Feynman said they were "tickling the tail of a sleeping dragon". The only goal of these experiments was to see how close they could flirt with criticality.

sho_hn 2y ago

My understanding is that he was demonstrating a technique for how to bring the system to near supercriticality, without causing it. I.e. the objective was to look at the measurement devices they had and monitor them, and build an understanding of what the data was showing. This would then (in principle) be repeated by others with more specific objectives later. Obviously they should've built a rig for that (at least), but I guess there was a "ain't nobody got time for that" attitude.

dale_glass 2y ago
Right, but shouldn't distance be a critical part of such a measurement? Like if we measure the amount of noise a device makes, we do it in a quiet room and at a standard distance. Without precision there's no useful data being generated. So that's the part that I don't get. Shouldn't there be a screw being turned precise amounts, precisely made shims, or at least calipers be involved?
- sho_hn 2y ago
  I think it was more about being able to understand/read what the measurement devices were showing. The exact distance probably wasn't as important as the criticality could also vary with other variables (e.g. geometry). As in, you're trying to understand the situation as "shouldn't they have precisely nailed down all the parameters, if the goal is to measure when X starts happening". But it seems Slotin was more demonstrating "this is what you're going to see on the monitors when stuff is close to going boom". It wasn't about "this specific distance is a safe gap" and more "here's how you can tell whether the gap is safe". He was about to be reassigned out of the lab, and was demonstrating equipment to his designated successors.
- davisp 2y ago
  Sometimes science doesn’t have to be precise to demonstrate a result. Consider trying to measure feedback from a microphone and speaker. You don’t have to be an expert to know that there’s a quick change in system behavior when the microphone gets too close to the speaker.
- StableAlkyne 2y ago
  The honest truth is there's just a certain acceptable level of jank in a scientific lab. Not everything needs to be measured to a high precision to be useful, and it's always a balance of how much effort you want to expend versus how useful that extra accuracy/precision is. If all you care about is "when you're getting close to a critical mass, your instruments will look like this," you don't care that you have a wide swing in your data. You just want to show a difference from baseline.
- stetrain 2y ago
  If the goal is to collect precise data and use it after the experiment to draw conclusions, update a model, etc. then sure. If the goal is to demonstrate to observers how the neutron output (reaction rate) increases as the reflectors are moved closer together over the source, then that isn't really necessary. This seems more like an incredibly dangerous version of a demonstration you might see at an interactive science museum or a classroom. You don't need precise measurements to demonstrate the relationship between two phenomenon.
- rocqua 2y ago
  This is just proving 'move spheres closer means more neutrons'. It's something you quickly show someone to explain what you are going to do. The people watching will then get most of the same ideas you are suggesting, and figure out how to design a proper experiment around it. Presumably the experiment to be done later is about characterizing different cores. They had already done it for this core, and wanted to teach the principles to others.

lm28469 2y ago

It's all in the wiki: https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core > It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core using a thumb hole at the polar point. As the reflectors were manually moved closer and farther away from each other, neutron detectors indicated the core's neutron multiplication rate. The experimenter needed to maintain a slight separation between the reflector halves to allow enough neutrons to escape from the core in order to stay below criticality. The standard protocol was to use shims between the halves, as allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion. > Because in my head, a proper experiment has data collection and precise measurements. In your head yes, in early nuclear science it seems protocols weren't that important as long as it went boom in the end. As with many industries, regulations are written in blood

dale_glass 2y ago
I've read that and it doesn't really answer those questions. How can you measure the core's neutron multiplication rate if you're not exactly controlling the distance? Isn't the measurement going to be all over the place?
- kstrauser 2y ago
  In a demonstration, not an experiment, it’s sufficient to have the Geiger counter go clicky at different rates while the demonstrator plays the sphere like a theremin. The point was to show it to people, not to collect data.
  - eichin 2y ago
    > plays the sphere like a theremin Wow, that's a brilliantly horrifying image. (Are there other analogous ones? Does anyone do musical timing of building demolitions, or something like that?)
    - 2y ago

deleted 2y ago

[deleted]

Grimblewald 2y ago

The problem with this image of science is that in order to properly collect things we have to properly understand things we could be collecting. We can certainly do our best, but sometimes unexpected things happen. Take x-rays and their incidental discovery via the effect of x-rays on nearby photo-film. Totally accidental data collection from work at the bleeding edge, which was work that has transformed society as we know it. Another point is that in order for things like the lab equipment to be sleek and well built, we need to understand needs. This means that any research that meets your criteria is quite likely not at the cutting edge of anything. Most cutting edge labs I know look more like someone raided the hardware/electronics store to build some abomination than the Hollywood sleek and shiny labs you might be picturing. The sleek well built shiny labs you are picturing tend to be corporate labs and the like, doing work on safe and predictable things with well defined scopes. Translating existing knowledge into marketable products is a lot easier than discovering genuinely new knowledge.

dale_glass 2y ago
This was after Hiroshima and Nagasaki, in a secret, government lab staffed by the utmost experts. It wasn't the "oh look, something funny happens if I do this!" stage of experimentation. This was after they understood what they were dealing with well enough to build and successfully use two bombs. And Slotin was supposedly about to move elsewhere and was working on passing on knowledge. That's why it's so weird to me.
- Grimblewald 2y ago
  Experimentation is _ALWAYS_ at the "oh look, something funny happens if i do this" stage, otherwise it isn't experimentation/research but rather research/development. If we know what to expect, why experiment? Why waste resources?

Aardwolf 2y ago

Put a half-sphere reflective shield around a nuclear substance which will make the substance more reactive due to neutron reflections. Due to a slip-up with the screwdriver that was supposed to hold it up, accidentally fully drop down the shield, causing the too large radioactive reaction I think with his reaction afterwards to remove it again, he saved the others in the room, but not himself

alt187 2y ago

Nothing. Richad Feynman said they were "tickling the tail of a sleeping dragon". The only goal of these experiments was to see how close they could flirt with criticality.