4 ms·

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!)

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!)