Comment by FiatLuxDave | Hacker News Reader

Comment by FiatLuxDave | Hacker News Reader

So, I have complicated feelings about this.

I'm only a few years older than David Hahn. In the early mid nineties, I was also building a nuclear reactor on the down-low. I got my first neutrons a few days before I turned 21. My name is even David as well. So, my friends would always compare me with him as soon as they heard his story.

I've always felt a bit of kinship with him, particularly his desire to learn-by-doing about nuclear physics. I've also felt a bit of jealousy at the press he got, pity for the mess he got himself into, and I'm not sure what to name the feeling (sadness? derision?) for some of the mistakes that he made. I'm not sure that I would have done better at his age, trying to do what he was doing.

There were things I did that were different from him, that I guess led me to a different fate. I made sure not to break any laws (deuteron colliders are under a different set of rules than radioisotopes). I went to college, which was probably easier for me than for him. I involved other people in my project, including getting VC funding. I sure never made a mess like he did.

I also made some similar mistakes. I wasn't even aware that high voltage power supplies would make x-rays. I was shocked and scared when Spence, our 'adult supervision' engineer, brought in a Geiger counter and showed us that we were making a fair amount of x-rays. I learned a lot of radiation safety on-the-job, quickly. Without Spence, who knows how badly I would have irradiated myself before learning on my own?

We always avoided publicity. Part of that was because we didn't want people freaking out that we were doing "nuclear stuff" in a rented office by the railroad tracks in Tallahassee. Our landlord knew, and was cool with it, but we were nervous about how the general public would react. So we kept things private.

I used to feel that maybe it was a mistake to keep my fusion project so secret. It certainly didn't help my career to be a failed founder with no published papers, without even a press release to point to for my years of work. But when I look at how the mistakes that David Hahn made followed him his whole life, and which weren't all that different from mistakes I made in my youth, I think maybe my decision wasn't so bad. "Radiation Safety Officer" happens to be one of my job titles these days.

Rest in Peace, David.

Thanks for your personal story. It was fascinating.

Do you think you could write about it at length in the future? I'd love to read more.

Maybe some other place. This is David Hahn's thread, not mine.

What kind of high voltage power supplies? Now you've got me worried as I played around with Tesla Coils, spark gaps, neon sign transformers a lot as a kid...

I think once you start getting potentials over 10 kV, the Schottky effect starts to give minor x-ray emissions.

The more major or typical source is from tubes. Most tubes at high voltages will emit x-rays, even if that is not their intent, from an emitted electron striking the anode. This is why CRT TVs usually used thick leaded glass, to block the x-ray emissions.

Well, the penetrating depth depends upon the voltage, and there needs to be space for the electrons to accelerate (this means vacuum or air, dialectric insulation in the air gap cuts it down). Anything above around 15 kV has 'potential' for x-rays which can penetrate beyond your skin and do some damage. We were working with 180 kV power supplies, with a 10 inch vacuum-filled free fall distance for the electrons, so we got a goodly amount of rays.

You can get x-rays off of Tesla coils, spark gaps, etc., but usually the dose rate is fairly low. It is worth measuring though, especially if you will be exposed for a long time or its close to your body. Typically it will be below around 1/100th of your yearly exposure limit per hour. So, if you are playing with one for an hour, no biggie. If you are planning on putting one on your 40 hour/week work desk, think again.

I once made a helmet for Halloween with a pair of Tesla Coils, one on each side of my head. The helmet was conductive, and it would look like the sparks from the coils were going through my head. This was not what I would call 'safe' (body-mounted high voltage can go badly wrong), but it was a lot of fun for one night. I made sure to keep the voltage below 20 kV, and reduced my exposure time by only running it when I wanted to impress people (mainly cute girls).

Hi. Newbie here, but I've been following this story. It sounds rather tragic.

This might be slightly off-topic, but is there any possibility that someone could conceivably "weaponize" an x-ray or gamma-ray emitter, e.g., for a terrorist plot?

I came across this article about an earlier half-baked plan from 2012. Some white supremacist had "allegedly planned to use a remote-controlled X-ray weapon hidden inside a van to vaporize Muslims in upstate New York and launch an attack on the White House." This seems to be stretching the limits of plausibility. (Obviously, this wouldn't have been some science fiction "disintegration gun.")

https://news.vice.com/article/this-kkk-guy-tried-to-build-an...

However, let's assume that we had some James Bond super-villain who had unlimited resources and a stable of highly-trained engineers and Nobel physicists as his minions. Would it be within the realm of plausibility to build such a thing? Or would this still be complete science fiction?

More specifically, could an emitter be be made that generates x-rays or gamma rays in a non-directional way so that everyone in the vicinity received a lethal radiation dose over the course of a few minutes? How much electricity would this take, and what type of potential range might it have? Would buildings or car doors tend to block the radiation? Would the victims somehow sense that they were being irradiated (e.g., a burning sensation)?

I'm not looking for technical blueprints or anything, of course. It's just a thought experiment. (Hi, NSA!)

Can you touch on ANY details of how this is possible with 'every day items'? When I think of a reactor, I think of something that looks super complicated and engineered, like CERN. It's hard for me to imagine how a reactor can be built by a boy in a shed... what materials did he need? What powers it? What (if any) safety measures are taken... even rudimentary ones?

You can read the book about The Radioactive Boy Scout:

https://www.amazon.com/Radioactive-Boyscout-Story-Nuclear-Re...

But IIRC the everyday items were smoke detectors with Americium and uranium from old painted clock dials. I think he found a full vial of dried uranium paint hidden inside some random old clock at an antique store.

Based on the details like deuterium fusion with high voltage, my guess would be that FiatLuxDave built a variant of a Fusor. It is a challenging project but not out of the reach of a dedicated high school student.

http://makezine.com/projects/make-36-boards/nuclear-fusor/

First nuclear reactor was basically a pile of graphite brics with nuclear fule placed at calculates positions.

You get to critical reactor with just assembling materials of correct chemical composition to a correct geometric configuration.

The most difficult part is probably acquiring the nuclear material.

I've never built one, though :)

https://en.m.wikipedia.org/wiki/Chicago_Pile-1

The physics what we are looking at is the fact that neutron capture requires neutrons that go at a very specific speed. So, the nuclear fule creates some initial neutrinos that go fast, the carbon slows it down to a sufficient speed that they are captures by rest of the fuel, which then causes more chain reactions.

This is the reason reactors are a bit delicate - not enough neutrinos or wrong speed - no reaction. Too much - booom.

Why do people keep repeating this? Reactors don't go 'boom'. They aren't thermonuclear weapons. The worst you'll get is a bunch of heat when the cooling system fails and a possible steam explosion.

It depends on the design of the reactor, doesn't it?

They aren't thermo-nuclear bombs. They are simple nuclear bombs.

The earliest types of nuclear bomb essentially smacked two sub-critical masses of nuclear material together to form a super-critical mass, or compressed a sub-critical mass to a greater density, such that it was super-critical at that higher density. Then the core material produces heat faster than it can be radiated away, and eventually explodes.

If the non-fuel components of the reactor are destroyed, there may be enough nuclear material present to combine into a super-critical mass. At that point, it will go boom unless someone acts quickly enough to stop it.

It just so happens that all reactors designed to actually be built are ultra-paranoid about not turning even a completely failed reactor into a nuclear bomb. In a backyard DIY reactor that is not following a design blessed by physicists and engineers, you might get a boom. You will more likely get a big, deadly, radioactive fire that drops toxic ash on innocent bystanders, but if you melt cylindrical fuel rods in a graphite moderator, and they pool in the bottom of a spherical containment vessel as one big, connected mass...

I will ask again: Why do people keep repeating this?

You keep throwing around ideas like "They are simple nuclear bombs". It's not like during WWII the US asked some physicists to make a weapon and they replied with "just put some of this in a box and drop it on Japan. Call us when you need more"

Here are multiple explanations as to why a reactor is not and can not be a bomb:

http://physics.stackexchange.com/questions/7149/why-does-nuc...

Did you get your education on nuclear power from the "The China Syndrome"?

"Boom" in this context I assume doesn't mean kilotons of TNT equivalent explosion, it means "criticality event resulting in the release of a lethal dose of radiation". At Los Alamos, Harry Daghlian was killed by the "boom" resulting from simply accidentally dropping a brick onto a core of nuclear material.

More on that:

https://en.wikipedia.org/wiki/Harry_Daghlian#Criticality_acc...

One of the design constraints of a bomb weapon is that it should not go off before you want it to explode.

Another constraint is that you have to be able to get it to the target area while someone is actively trying to stop you from doing it.

Finally, a weapon has to direct its energy such that it destroys the intended target, rather than dissipating most of it uselessly, or harming your own assets.

That's why the physicists didn't just say to refine some plutonium and lob it at the enemy.

There have been 60 criticality accidents, with 14 fatalities. None of these resulted in an explosion (excluding steam), but that does not mean that a criticality accident cannot cause an explosion. A lower critical mass will produce more "flash" than "bang". It can still make a boom. The pow from a cherry bomb is as much an explosion as that from a 500-lb military munition.

A failed reactor will not destroy any cities, like the first nuclear weapons. But it could destroy a back yard, and render the surrounding neighborhood uninhabitable for many years.

"Boom" was a bad imagery perhaps given the prevalence of nuclear weapons in the common thought, but not misplaced given the generality of the discussion - in this instance, I meant an interesting event consisting at least of a sudden spike in neutron flux and heat production.

A "reactor" in this instance referred to an assemblage of nuclear material and neutron moderator to create sustainable chain reaction. Without the cooling tanks and pumps required for power generation, or the compression mechanism required for a fission bomb.

If you assemble a particular configuration of nuclear material it will go super critical

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

What happens when the neutron flux increases depends on the circumstances.

As another commenter pointed out, even this can be lethal https://en.wikipedia.org/wiki/Demon_core

> First nuclear reactor was basically a pile of graphite brics with nuclear fule placed at calculates positions.

Well, there's also this. :) https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...

It's 'relatively' easy to build fusion chambers - people do so in their own homes. [1]

[1] https://en.wikipedia.org/wiki/Fusor

It wouldn't be inconceivable for a determined person with some electronics experience to make a cyclotron [1], which is a neutron gun that can produce radioactive material. Not sure if "reactor-in-my-garage" folks are doing this, or if the material it produces can be used in any subequent reactions.

[1] https://en.wikipedia.org/wiki/Cyclotron#Usage

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