X radiation exposition

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Arnau Vivet
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X radiation exposition

Post by Arnau Vivet » Tue Dec 12, 2017 4:49 pm

Hello,

I’ve been doing some tests with my fusor earlier and I’m now worried about my own safety, I run this fusor on about 50 KV 10 miliamps in a vacuum about 1000 microns for about one minute at aproximatelly one meter of it, is there any formula I can use to determine the level of X ray radiation I’ve been taking, is it really bad?

ian_krase
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Re: X radiation exposition

Post by ian_krase » Tue Dec 12, 2017 5:00 pm

Get a Radiation meter. (you should have one already. Not very expensive.)

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Dennis P Brown
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Re: X radiation exposition

Post by Dennis P Brown » Tue Dec 12, 2017 5:20 pm

I agree you need a Geiger counter or at least a dosage badge (either of these can be obtain rather inexpensively as old CD units; just remember, you often get what you pay for - so, having surplus units will not prove if you have a threat; only that one might be present.) So, unless you buy calibrated units, any radiation device will only give an approximate idea on the dangers.

Your voltage and current are capable of creating a dangerous x-ray flux/hazard so shielding is very likely required and should have been installed regardless of knowing the threat level - that should have been common sense obtained by reading on this subject.

To get the formula to calculate the possible radiation levels simply Google x-rays on the wiki and read the article - then cross reference to absorption of radiation; certainly, first read the FAQ's here on radiation hazards!

Your particular threat is dependent on a number of parameters (for a fixed voltage/power.) You also need to know the chamber material, and thickness; also, ditto for any windows. Then using geometry and these values you can calculate the x-ray threat (No, this is not easy for an accurate number - to get an upper bound, ignore all this and just calculate the threat with no material except air from a xray flux created by that power/voltage on a steel target. Again, that is why a radiation measuring device is essential for any units operating above NST levels.) Without that information on your device/chamber, it isn't possible to evaluate the threat by anyone; critically - remember, dosage is cumulative so singular time events alone does not capture the total danger! Total dosage matters immensely and that requires adding up all the time from all exposures.

This is a good lesson in the dangers of using any high voltage/power device and not reading the FAQ's on the hazards of radiation nor assuming that one can just use high voltage systems without any research relative to safety. Remember this: YOU AND ONLY YOU ALONE ARE RESPONSIBLE FOR YOUR SAFETY AND DETERMINING ALL DANGERS!

That said, it is not likely that for one exposure for one minute at one meter distance you were irradiate enough to posse a short term health hazard; however, I am guessing since I am assuming you have a steel chamber and had only a single exposure.

Arnau Vivet
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Re: X radiation exposition

Post by Arnau Vivet » Tue Dec 12, 2017 6:12 pm

Oh, okey, you see I already knew that it was producing X rays, I just got so hyped when it worked that I couldn’t think clearly enough to think about the consequences, I’m a bit scared now but I think it will be enough by not turning it on again. Thanks

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Jim Kovalchick
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Re: X radiation exposition

Post by Jim Kovalchick » Tue Dec 12, 2017 7:30 pm

1000 microns? I have never heard of a fusor running at so high a pressure.

ian_krase
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Re: X radiation exposition

Post by ian_krase » Tue Dec 12, 2017 8:12 pm

Yeah, unless you have known good voltage instrumentation, you may not have been at that voltage.

Beware of CD radiation meters and dosimeters. The most common and inexpensive ones are only sensitive to seriously hazardous radiation (made for nuclear war...) as opposed to the substantial but not immediately dangerous doses you may get from a powerful but poorly shielded fusor. The CDV meter that's actually a geiger counter (with a detachable probe over the handle) is a good option, but in modern times there are many better options you can DIY.

Arnau Vivet
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Re: X radiation exposition

Post by Arnau Vivet » Tue Dec 12, 2017 9:26 pm

Yeh, my fusor doesnt make any fuion because of the low vacuum achieved and I also use normal air in it’s tests, but even though I think it does produce x-rays because of the high voltage

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Dennis P Brown
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Re: X radiation exposition

Post by Dennis P Brown » Tue Dec 12, 2017 10:54 pm

Your poor vacuum certainly would be an issue if you had deuterium. In any case, as you see, your next focus should first be shielding - learning what you need and where to use it. Then, consider getting a better vacuum (leaks? or is your pump not a two stage?) With good shielding and being careful, radiation issues can be minimized even without a detector.

Maybe after addressing these issues, your need for deuterium gas can be addressed.

Even then, that isn't sufficient since one must be able to measure any neutrons produced.

In any case, your power supply sounds fusor capable so you have a good start that few beginners generally have. Just be extremely careful with that supply - it is also extremely lethal voltage/power wise regardless of the x-rays. Use only HV proper cables rated to at least 50 kV and be certain any fusor is properly grounded - read the FAQ's on the safety of high voltage for fusors (NEVER allow your transformer to float!) I use shielded/grounded high voltage cables to be certain my system is safe. Also, my x-former is in a metal, grounded case (which my HV cable shielding is connected to.)

Finally, before you burn out your x-former, read about using a ballast resistor in the HV circuit when arcing across/creating a plasma in poor vacuums (that is you have a very high conduction path to ground - translation: you have shorted your x-former to ground - a great way to melt the secondary windings without a ballast resistor) - there is a FAQ just for that ballast issue as well as on how to properly wire in a milli-amp meter (critical for all fusor operations.)

I would fix those issue before trying to run the x-former again through a plasma.

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Re: X radiation exposition

Post by Niels Geerits » Tue Dec 12, 2017 11:29 pm

The current voltage and pressure combination you mentioned seems unlikely to me. See the following FAQ viewtopic.php?f=24&t=2795 At 1 Torr and 5mA you he only had about 400V across his fusor. Your voltage was probably also in the ~1kV range.

As for a formula. You can come up with one pretty simply if we assume a high vacuum and therefore a large mean free path: Find the single electron energy: E=e*V (e is the electron charge), this is the energy of the highest energy X-Rays your fusor can produce. Calculate the number of X-Rays being produced per second from the current: j=I/e. Now calculate the X-Ray flux by dividing this number by the internal area of your fusor: J=j/(4pi*r^2)=I/(4*pi*e*r^2). Next you will have to look up the x-ray xsection of your fusor shell material, at the relevant energy, and then calculate the macroscopic xsection of the fusor shell. OR there should also be tables that show how much steel you need to reduce the x-ray dose to half, one fourth, one eigth etc. from that and your fusor shell thickness you can calculate how many X-Rays leave the fusor. Call this J'. Finally calculate the X-ray flux through you (Jy) Jy=J' * (r_fusor^2/r_you^2), Where r_fusor is the radius of the fusor and r_you is the distance between you and the center of the fusor. Jy is the number of X-rays per m^2 per s going through you. Now you have to calculate the number of x-rays that are absorbed by your body per second and multiply this by the X-Ray energy to obtain the energy absorbed by your body per second: P_abs=Jy*A*e*V (A is the area of your body, this is a rough estimation which is more accurate if you are "far away" from your fusor. Also note that I am being lazy under the guise of being conservative by assuming that all x-rays will be absorbed by your body). Now just multiply this by the exposure time and divide by your body mass to obtain the dose in Sieverts: D=P_abs*t/m=J' * (r_fusor^2/r_you^2)*A*e*V*t/m.

I dont know how close these calculations will get you to your actual dose but it should give you an upper limit if I am not mistaken. If you cannot calculate J' just assume J'=J, this will also give you an (even higher) upper limit.

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Dennis P Brown
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Re: X radiation exposition

Post by Dennis P Brown » Wed Dec 13, 2017 2:09 am

Good overview for calculating worse case x-ray threat; issues of solid angle and that very few electrons are at the max voltage will drastically reduce the actual x-ray's at the highest level but it is best to work with upper bounds for first level calculations as you point out.

The thread you reference has little to do with the voltage that can be maintained by large transformers designed for plasma work. The example they used was a NST which always has low voltage output soon after the plasma ignites. My x-former has no issues holding 32 kV at 15 microns as well as 23 ma or higher (recent work posted the other day had 50 kV at 50 microns and 4.2 ma) - in the thread you posted their experiment does not relate to real fusor x-formers because their x-former is designed to have its voltage drop to a few hundred voltages at plasma start up; of course, that is why any NST (even if their voltage was raised high enough at their start) would not be useful to work for a fusor.

Once must be careful distinguishing between break downs like arc's (30 kV/cm in air) and steady plasma's (lower pressures at various voltages) - this is more complex a problem and hard to generalize; issues like their system's geometry/electrode configuration and actuate pressure and x-former design all will come into play determining their voltage/current and pressure for given conditions.

As for a full amp at 50 kV, that is more likely just a mistake as I mentioned previously.

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