12 ms·

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 th

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.

echelon 10y ago
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.
- FiatLuxDave 10y ago
  Maybe some other place. This is David Hahn's thread, not mine.
iamleppert 10y ago
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...
- planteen 10y ago
  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.
- FiatLuxDave 10y ago
  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).
- jacobsor 10y ago
  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-x-ray-weapon-to-kill-muslims-and-obama-feds-say 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!)
Exuma 10y ago
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?
- paulcole 10y ago
  You can read the book about The Radioactive Boy Scout: https://www.amazon.com/Radioactive-Boyscout-Story-Nuclear-Reactor/dp/1841152293 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.
- keenerd 10y ago
  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/ http://makezine.com/projects/make-36-boards/nuclear-fusor/
- fsloth 10y ago
  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 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.

echelon 10y ago

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.

FiatLuxDave 10y ago
Maybe some other place. This is David Hahn's thread, not mine.

iamleppert 10y ago

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...

planteen 10y ago
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.
FiatLuxDave 10y ago
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).
jacobsor 10y ago
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-x-ray-weapon-to-kill-muslims-and-obama-feds-say 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!)

Exuma 10y ago

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?

paulcole 10y ago
You can read the book about The Radioactive Boy Scout: https://www.amazon.com/Radioactive-Boyscout-Story-Nuclear-Reactor/dp/1841152293 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.
keenerd 10y ago
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/ http://makezine.com/projects/make-36-boards/nuclear-fusor/
fsloth 10y ago
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 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.