Making 'The Blue Flash': How I reconstructed a fatal atomic accident | Hacker News Reader

Making 'The Blue Flash': How I reconstructed a fatal atomic accident

bbc.com

92 pointsHooke61 comments

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?

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.

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 - thanks to toomuchtodo for the reference.

Thank you! Answers a nagging question I’ve had for a while.

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.

https://en.wikipedia.org/wiki/Demon_core

https://en.wikipedia.org/wiki/Louis_Slotin

A careless slip led to a fatal accident in the Manhattan Project - https://news.ycombinator.com/item?id=36798594 - July 2023 (1 comment)

The Demon Core and the Strange Death of Louis Slotin (2016) - https://news.ycombinator.com/item?id=36022373 - May 2023 (59 comments)

The Demon Core and the Strange Death of Louis Slotin - https://news.ycombinator.com/item?id=25317021 - Dec 2020 (1 comment)

Demon Core: The Strange Death of Louis Slotin (2016) - https://news.ycombinator.com/item?id=20744425 - Aug 2019 (22 comments)

Demon Core - https://news.ycombinator.com/item?id=20205876 - June 2019 (55 comments)

The blue flash - https://news.ycombinator.com/item?id=11754713 - May 2016 (1 comment)

Demon Core: The Strange Death of Physicist Louis Slotin - https://news.ycombinator.com/item?id=11749742 - May 2016 (34 comments)

"A careless slip" is really understating it. "A completely irresponsible and reckless indifference to safety" would be more like it.

If you want to look at it with 21st century eyes, sure. Things were VERY different back then though. What you would call prudent and common sense safety measures, they would have called something that you would think they should be fired for saying. And the boss would have sided with them.

What evidence do you have for this? There seems to be a lot of romanticism for an imagined can do spirit, and either people died, as they did in this case, or people understood risks and took action to mitigate them.

Not the GP but I’ll answer on their behalf:

- https://uk.news.yahoo.com/us-military-once-detonated-nuclear... (5 volunteers stood directly below a detonation)

> In the aftermath, the five men shake hands, congratulating each other.

> "My only regrets right now," Col. Bruce says, "are that everybody couldn't have been out here at ground zero with us."

- https://www.telegraph.co.uk/global-health/terror-and-securit... (Around 22,000 British servicemen, along with soldiers from New Zealand and Fiji, took part in the tests)

> Safety guidance on the day was, he recalls, scarce: personnel were advised to wear a hat and make sure their sleeves were rolled down. The men were then ordered to “sit down with your back towards the blast area and cover your eyes.”

> Despite assurances given at the time that the tests posed little risk to health (via radiation exposure), a significant number of veterans went on to experience significant repercussions.

- https://www.livescience.com/1698-atomic-bomb-test-exposed-ci... (First Atomic Bomb Test Exposed U.S. Civilians to Radiation)

> Because of its importance in the war, the Trinity test was conducted in secret. Little was known about the dangers of radiation exposure in the 1940s, so local residents were not warned or evacuated in advance of—or even following—the test. As a result, people in surrounding areas were exposed to radiation by breathing contaminated air, eating contaminated foods, and drinking affected water and milk. Some ranches were located within 15 miles of ground zero, and commercial crops were grown nearby.

The stories about these are not romanticised. They’re conveying our ignorance. There is nothing romantic about people dying from radiation.

Oh the immediate parent to me seemed to suggest something like this was all a good thing, but thank you for driving the point home that it was a bad thing, even at the time.

The assembly that killed Slotin was supposed to be used with safety spacers to avoid this specific accident type. He would have been alive if he used them. Fermi infamously warned the physicists, including Slotin, that they will be dead within a year.

Not sure if you saw the sibling comment but in case you haven't:

> Enrico Fermi himself had warned Slotin that he would be “dead within a year” if he continued (the way he was working)

Some risks were absolutely known.

No, it's that familiarity breeds contempt, even when the consequence is death. Writing it off as "irresponsible and reckless" downplays that this wasn't someone being an idiot, it was a standard human behavior.

I think even at that time not everyone would agree and would have actually called him an idiot...

"Enrico Fermi himself had warned Slotin that he would be “dead within a year” if he continued—but the exigencies of the Second World War had privileged expediency over safety. "

It was irresponsible and kind of reckless.. especially after a similar thing had happened: "Nine months to the day before Slotin’s accident, Daghlian had been working with the very same plutonium core, performing a different criticality experiment that used tungsten-carbide blocks instead of the beryllium tamper.* He dropped one of the blocks, and the core briefly went critical. Daghlian took nearly a month to die."

My standard human behavior might have been proactively that of the guard: "But when the core started to glow and people started yelling, he promptly ran out the door and up a nearby hill. " :D

( https://www.newyorker.com/tech/annals-of-technology/demon-co... )

I don't want to cry clickbait, but I really thought radioactive material was going to be involved here. Like, setup the accident again with a machine handling the screwdriver. I was very dissapointed to read about an artist's rendition of the accident.

As you can see in other comments, this is a very interesting topic! I think that the shared article adds relativley little, though.

...you thought someone was going to be able to get a critical amount of fissile material (originally plutonium) and bring it together using a machine???

I cannot possibly express how thankful I am that doing so is just about impossible for any layman.

Famously, they tried to recreate it once. And slipped. And people died

What about the title implies only laymen were involved? I had no idea going into it who would be doing what.

You thought nuclear security professionals were going to recreate an incredibly expensive nuclear disaster which killed a guy, except actuated by a machine with the humans at a safe distance? And that would have been more educational than just building a model of the thing with a painted foam core?

Journalists -and scientists for that matter - don't usually have access to highly enriched fissile material. Nobody would get permission to do this without a very, very good reason.

Sure, and maybe there's a way to approximate it? I don't know. I'm not particularly well versed on this topic, but when I hear "reconstruction of Foo" I imagine, well, a reconstruction of it. Not an artists visual interpretation of it. This is the first time I've ever seen a recreation in a purely visual sense.

I'm with you. Love the topic. The pictures look excellent. Clearly this is a talented artist. I think a more accurate title might have been "I Painted Pictures of Pictures of Aspects of the Blue Flash." There really wasn't much recreated here.

Looking at how they worked with radioactive materials back then, it feels rather amazing that we're still here today.

I guess articles like these are starting to pop up as we approach August 6...

What is August 6?

The anniversary of the Hiroshima bombing.

The day of the Hiroshima bomb.

https://en.wikipedia.org/wiki/Hiroshima_Peace_Memorial_Cerem...

The US throw nukes on Japan. August 6. Hiroshima and three days later, August 9. Nagasaki.

Don't forget there are "lost" nuclear bombs all over the world including North Carolina.

"oh well we can't find it, we're got plenty more anyway, what's the worst that could happen someday when everyone forgets it's there"

https://www.bbc.com/future/article/20220804-the-lost-nuclear...

> a B-52 broke up while flying over Goldsboro, North Carolina, dropping two nuclear weapons to the ground. One was relatively undamaged after its parachute deployed successfully, but a later examination revealed that three out of four safeguards had failed

Okay, that's scary. I can just imagine someone looking to improve efficiency or cost savings thinking that four safeguards is over-engineered.

Sam Harris podcast episode 210[1] had guests William J. Perry, former Secretary of Defense and founding member of Nuclear Threat Initiative[2], and his grand daughter Lisa Perry, Communications Director at At The Brink[3], to talk in large part about that scary aspect of nuclear weapons, and how an accidental nuclear war is more likely than a deliberate one.

[1] https://youtu.be/NVnwc4rZI_0?t=12m40s Episode 210 (no paywall)

[2] https://www.nti.org "focused on reducing nuclear and biological threats"

[3] https://atthebrink.org Podcast about the modern situation with nuclear weapons

My understanding is that all of the safeguards worked as intended and characterizing them as 'failed' is a bit unfair.

The three that "failed" were designed to prevent the bomb exploding on the runway (before take-off), on the plane (before being dropped), or in the air (before the plane could escape).

Since this event involved a plane taking off, dropping the bomb, and the bomb parachuting to the ground - it was largely indistinguishable (to the bomb) from an actual intentional event. Only the cockpit Safe/Air/Ground selector prevented detonation.

Note that the cockpit selector did fail in other incidents, arming bombs while still in the 'safe' position due to a short circuit elsewhere.

Here's a fun/terrifying Wikipedia rabbit hole for you:

https://en.wikipedia.org/wiki/List_of_military_nuclear_accid...

I think my favorite is when we accidentally dropped a nuclear bomb in someone's yard in South Carolina.

August 6, but more importantly the last few weeks there has been a flurry of articles about the Manhattan Project and the a-bomb, probably due to the release of the Oppenheimer movie.

> Looking at how they worked with radioactive materials back then, it feels rather amazing that we're still here today.

Nowadays, the dangers of exposure to radiation have been well publicised and I'd guess that most people over-estimate the dangers as plutonium can be handled quite safely (unless it goes critical of course). They used to regularly carry plutonium core halves in their lab coat pockets - one half either side of their body.

From https://worksinprogress.co/issue/the-most-dangerous-substanc...

> Plutonium needs to be handled with care. You must avoid a critical mass. If you are machining or grinding plutonium as is required in reprocessing used nuclear fuel for solid-fuel reactors, you should avoid breathing the dust. But because it is a slowly decaying alpha emitter with very inefficient body uptake, it is one of the more easily handled toxic substances known to man. Our fear of plutonium is totally overblown.

By my calculations, under some reasonable assumptions, the 'demon core' at the time was still a ~16.9 GBq alpha and gamma emitter when not undergoing a chain reaction (maybe more since its earlier criticality accident may have meant it had a higher proportion of shorter half-life elements).

Calculation: Assuming 7% Pu240, 93% Pu239, (-(log 0.5 / (6560 * 365.25 * 24 * 3600)) * 6.02214076E23 / 240 * 0.07 -(log 0.5 / (24100 * 365.25 * 24 * 3600)) * 6.02214076E23 / 239 * 0.93) * 6.2 / 1E9 = 16.89 GBq.

Admittedly, in the scheme of things, that's not that high, but criticality aside, handling it unshielded on a regular basis is not something that would be considered acceptable these days, especially not for a 'demonstration'. In 2023, when a 19 GBq sealed source (i.e. only slightly more activity) was lost in Western Australia when it fell from a truck, it sparked a massive search of a vast region, and the public were warned to keep a distance of 5 m. Obviously, they were worried someone would put it in a pocket or something for an extended period of time, and brief exposures wouldn't be that significant - but industrial radiographers working with similar sources, for example, would not get close to the source while it is unshielded and open.

The amount of alpha radiation isn't a problem as that'll be stopped by a layer of skin etc. Plutonium mainly emits alpha with only a little gamma.

I'm still confused about what was actually being done and why. Like what's the purpose of this experiment? What are the outputs, what does a successful result look like and what does a failure look like?

So I take it that positioning the reflector over the plutonium core generates more or less output from the sphere. Was somebody measuring that? But if so surely the actual precise distances involved are important?

So if the point is "how close do we have to get to get to X output", then surely distance measuring is of critical importance, and a screwdriver is completely unsuitable for that task.

Now I get it was a demonstration, so the actual data output may not have been important. But still, the person you're teaching needs the actual useful results when they do the experiment for real, so surely they will need something other than a screwdriver?

The author is an author and an artist who wrote and illustrated an article about the accident. The goal of the reconstruction he has done is to provide realistic drawing models

dale_glass is asking what goal Slotin had in 1946, not what goal Platts-Mills had today.

oh my bad

[repost]

i was fascinated with the criticality accident that claimed Slotin's life when i first learned about it. in particular, the schematic estimating everyone's distance to the apparatus and how much radiation they may have been exposed to: https://en.wikipedia.org/wiki/Louis_Slotin#/media/File:Sloti...

there was a second sketch made from that drawing which i also found fascinating. it doesn't add any additional information or analytical ability, but is just a sort of interesting and slightly dark translation of a rote schematic diagram into an artistic rendering of the event: https://en.wikipedia.org/wiki/Louis_Slotin#/media/File:Sloti...

I searched around for awhile trying to find the purpose and/or author of that second sketch but to no avail. however i did use it as the cover for an EP i released. please enjoy!

https://open.spotify.com/artist/37U37SYaXf1varqMgmpHkc?si=zE...

You can see this in the movie Fat Man and Little Boy

https://www.youtube.com/watch?v=AQ0P7R9CfCY

I love the "draw chalk outlines around your feet so I can work on if you're going to die or not since we know I am" moment.

Fabricated though, like the falling cup. The story as told by Schreiber in his memo on the accident is here:

https://www.halflifeofgenius.com/slotin

What? You mean that the producers of a film used creative licensing to tell a story of a “based on actual events” event is not 100% exactly what happened because what happened is really boring so they spiced it up a bit?

You want to nit pick that the telling of the story has been tweaked, but you totally let the fact the actual incident didn’t happen until well after Fat Man and Little Boy had both already been dropped and the war was over, so the incident had nothing to do with the Trinity Test?

Golly, that is a lot of hostility. I know how movies work, and just thought you and other readers may be interested in reading the non-dramatized retelling, having read it for the first time myself earlier in the day. FWIW, I didn’t think it was really boring, I thought it was interesting, especially to compare to the film retelling, hence why I shared it here.

Wowee.

Wowee? Hostility? Your fact check got fact checked. You come out like your clearing the story, but you only told part of the story that was convenient to your narrative. You took some creative licensing just like you’re critiquing someone else’s decisions.

My "narrative?" Holy cow, I have no idea what your problem is. Your reaction is unreasonable and I have to assume doesn't actually have much to do with what I posted. You are quite apparently reading an attitude into my post that I absolutely did not write into it. My sharing the true story behind a fictionalized retelling you enjoy was not meant as an attack on you or a smarmy "fact check," it was just to share the true story in context to the retelling. I read HN for intellectual curiosity and that's why I post things here too. This isn't the comment section on some politics website.

By the way, HN's community guidelines:

>Converse curiously; don't cross-examine. Edit out swipes.

>Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.

You have assumed bad faith and are swiping at me as you cross-examine your theory of why I "really" posted what I did, which is wrong. That's why I didn't break down the entirety of the movie's correspondence to reality, because you are imagining, and insisting, I was doing something here that I am not.

** edited out the rest because I won't argue about whether I was trying to pick an argument either. Take my word for it, you are completely wrong in your characterization of why I conversed with you with something I thought was of mutual interest. Good luck to you.

The infamous Demon Core[1].

[1] https://en.m.wikipedia.org/wiki/Demon_core

They didn't show that in Oppenheimer.

I thought this to myself as well after seeing Oppenheimer. As someone else has mentioned, it was shown in Fat Man, Little Boy. Each movie had different things that were or were not shown. FMLB didn't have the football field. There's only so much you can put into a 3 hour film where at least 7/8ths are in focus.

Edit: Diving down a rabbit hole, it looks like the scene in FMLB was based on the Louis Slotin incident from May 21, 1946. So some creative licensing from the producers, and probably why it is not in Oppenheimer

I wish I had something witty to add here, other than - "LOL". Thank you!

There's a saying in the camera department where the AC wants to buy a stop from the DP. I have always wanted to use that line, but I've never had a DP shoot that shallow for those kinds of scenes. In music videos, sure, but man! I haven't had the time to look into what was used to shoot that, but I'm wondering if they were shooting T-.95 it was so shallow.

What’s really interesting is how young everyone involved was.

When I got back from the army, I showed the girl I was staying with a picture of my sergeant and told her that was my boss. She said, "No way, he's too young to be a boss!" FFS, he was at least 25.

Look at the famous photo of the Enola Gay crew the morning of the bombing. Pictured and 12 of the 14 men who would be the first to drop a nuclear bomb. Half of them look like they should still be in highschool and the other half aren't looking much older either.

Oppenheimer wasn't there. This happened in 1946 and he had already resigned many months before

I was surprised they mentioned the bombing of Tokyo. Just short in a sentence, but still ..

https://en.wikipedia.org/wiki/Bombing_of_Tokyo_(10_March_194...

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