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Comment by lofatdairy | Hacker News Reader

>I have worked in a plant where I had half a critical mass in this hand, barehanded and dressed in street clothes, and half in this hand, wearing a lab coat, and I’d put this half in a pocket on this side and this half in a pocket on this side and walk down the hall. If those two ever got together, there’d be a blue flash. They never got together because I was between them.

There's "our design docs are photos of whiteboards" normalization of deviance and there's whatever the hell this is. Absolutely bonkers that there wasn't a demon core-like incident.

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The article writes about it like it was an element of 1950s iconoclasm.

Unfortunately, it never really went away.

https://www.science.org/content/article/near-disaster-federa...

Cherenkov radiation is pretty common in nuclear engineering, and occurs naturally in a number of contexts. It’s not some forebear of doom.

Otherwise, a great article!

I got to see Cherenkov radiation once on a high school class trip with only water between me and the blue glow!

Being a teenager I asked “what would happen if I jumped into the reactor?”

The researcher (this was a medical and research reactor) laughs and says “well, if you just jump into the water and splashed around we’d have hell to pay with filling out an incident report to <something important sounding, I forget>, but physically you’d be fine since the water shields you from the radiation. If you did a swan dive down toward the glow your skin would all melt off before you got to the reactor” maybe he was just saying this for effect but it’s always stuck in my head that water is a really, really good insulator against radiation.

> water is a really, really good insulator against radiation.

Absolutely. There is this[1] horror story about a diver who was doing maintenance in a transfer pool next to two spent fuel pools. After he was done with the work he found an unidentified object at the bottom of the pool and was instructed to put it in his tool basket. The object was a broken piece of irradiated reactor component. They realised that something is very wrong when the diver was lifting the basket out of the water and the area radiation monitors started to alarm, so they lowered the basket back into the water.

On the 10th slide of the document there is a diagram showing the water's shielding as a function of distance. At 1.4 meters there is no dose they can measure while they measure extremely high doses at centimeter distances.

1: https://isoe-network.net/publications/pub-proceedings/sympos...

I think you need power densities much higher than the shielding of an MPRR you saw to melt skin away. You'd probably get some bad radiation sickness and maybe even die instantly within a short radius, but not have the Hollywood skin melt.

Relevant XKCD: https://what-if.xkcd.com/29/

""" So, as far as swimming safety goes, the bottom line is that you’d probably be ok, as long as you didn’t dive to the bottom or pick up anything strange.

But just to be sure, I got in touch with a friend of mine who works at a research reactor, and asked him what he thought would happen to you if you tried to swim in their radiation containment pool.

“In our reactor?” He thought about it for a moment. “You’d die pretty quickly, before reaching the water, from gunshot wounds.” """

Actually, at a depth of 3-5 feet the bullets wouldn't hurt you: https://www.google.com/search?q=bullets+in+water

All is fine until you see it in the air. ;-)

Good grief. That's the most infurisating thing I've read in a long time, and I already knew a lot of tha background/historical incidents.

I have worked in a plant where I had half a critical mass in this hand, barehanded and dressed in street clothes, and half in this hand, wearing a lab coat

So they were only wearing a lab coat on one half of their body? I'm confused.

Or maybe they had three hands, they're only mentioning two of them, and the lab coat is intact

One lab coat, one pair of jeans. Half core in lab coat pocket, half core in jeans pocket, to prevent the lab coat pockets from coming into contact if they were in opposite pockets of the lab coat.

Safety first!

What's wrong with design docs being on a whiteboard? Not every company has time to painstakingly draw pretty UML diagrams in Figma when there are features that need to be built!

A whiteboard is a great tool to quickly iterate towards a shared understanding of the design at that point in time.

But if you take a photo of it and think you're done with documenting your design, you A) lose most of the context of the decisions that were made to arrive at that design. And B) have ensured that your documentation will get outdated and become useless pretty soon. You've basically decided not to have design documentation but filled yourself into believing that you do.

If you are serious about documenting software design to help future developers understand the system, you really do need those diagrams in a digital, easily updateable format and with textual explanations of the underlying decisions. And if doing that seems more work than it's worth, do it anyway, just with less details.

You joke, but I once worked on a team where nobody was able to point me to any coherent high-level documentation of what the system actually _did_... they all just walked around referring to it by some proprietary name as though you were some type of misinformed dunderhead for not understanding them. It took two hours of a manager talking and filling up a wall-sized whiteboard for me to discover that it was just a hideously over-engineered amalgamation of a CDN and document repository. If they'd had a diagram, README, or had even been able to give me the one-sentence overview then I suspect that the project's head count and productivity would have looked much different.

This is all to say that if you 1) invent novel terminology for things that already exist, 2) don't document anything, and 3) run your team like a high school clique then you never have to worry about finding yourself out of a job. Thankfully my current gig has loads of video training and an interactive dictionary for proprietary terms in an attempt to combat this.

And all the silicon valley layoffs, likely filled to the brim with people that conscienciously documented their replaceability for their employer, will look at that "high school clique" and remark "that's how you deal with sociopathic management".

Yeah, eventually management will nuke the whole division, but at least it provides those with jobs a bit more runway.

How much of the bemoaning of such adversarial tactics by engineers themselves is simply annoyance at what it causes them at their jobs, or the fact they have internalized pro-management propaganda?

> They never got together because I was between them.

I don't know how confident I would be about this, given that our body is mostly made out of a very good neutron moderator (water)…

Alpha radiation can’t penetrate the skin

This has nothing to do with alpha rays (which are helium nuclei), but with neutrons, and fast neutrons are much less prone to generate a fission than thermal neutrons, so having a moderator in between your fissile material parts reduces the amount of fissile material you need to achieve criticality. That's how nuclear reactor work, by the way. And this is also what happened to John Bistline on the 4th of June 1945 at Los Alamos.

Edit: in fact the first ever recorded criticality accident ever recorded involved the water in the body of a scientist (Otto Frisch), though the water was acting as a neutron reflector here, and not as a moderator.

People walk around with a loaded gun in their pants. They just (usually) carefully manage not to pull the trigger.

Would it be better to walk down the hall twice? Slightly, sure. Turns out it wouldn't have made a difference that we know of.

Guns don't tend to go off just by the mere presence of another unexpected gun nearby, though.

They do tend to go off if people finger the trigger though.

Somehow I think it’s more likely people will fiddle with their loaded gun than with two halves of a nuclear bomb.

> I’d put this half in a pocket on this side and this half in a pocket on this side and walk down the hall.

I'm inclined to see that as uncomfortably close to fingering the trigger.

With one half in the pocket and the other in hand (while it's being placed into the "safe" other pocket) nothing prevents the latter from going unintendedly close the first.

Yep. Or you trip and fall, they spill out of your pockets, and someone helpfully fetches them for you.

What if two people walk down the hall doing the same thing in different directions? ... Oh I forgot my slide rule ... !#FLASH#! ... what was that!? Oh shit.

Half joking. Is the material and spatial separation of a lab coat enough to prevent a reaction between two lumps of plutonium of sufficient combined critical mass? It might be since it's so bad at penetrating anything solid, but I don't know.

Considering the original demon cores were held apart by a screw driver, the answer is technically yes.

It's still a horrifyingly unsafe thing to do.

https://en.wikipedia.org/wiki/Demon_core#/media/File:Ticklin...

Technically, it was the neutron reflecting sphere was was held apart by a screwdriver.

The Hollywood version of events: https://www.youtube.com/watch?v=AQ0P7R9CfCY