NST Troubles & X-ray Protection

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Jeff Duncan
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NST Troubles & X-ray Protection

Post by Jeff Duncan »

Hello all,

After roughly 3 months of absence due to academics (Finals, SAT, College applications, etc), I have finally been able to resume studying fusion technology in the hopes that in the following months, I construct a fully functional demo fusor that, with time and patience, can be turned into a neutron producing fusor. I successfully constructed Maker Magazine's “star in a jar” (I understand that this is hardly advanced and virtually considered an art project) and ran the apparatus a couple of times before taking the aforementioned long break. I carefully stored away my materials, and upon my return to my experimentation, I found that the NST had secreted some oil while it was stored away. Below are pictures; I wanted to ask some of the experienced folks on here what this was and what it means for the NST’s future capabilities.
Image of NST that secreted oil after being stored
Image of NST that secreted oil after being stored
Additionally, though this may seem absurd, I ran the apparatus powered by the 15Kv, 30ma NST with no X-ray protection. Was this irresponsible? If so, where can I research how to determine when exactly X-ray protection is required and how to protect myself properly?

Thanks,
Jeff.
JoeBallantyne
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Re: NST Troubles & X-ray Protection

Post by JoeBallantyne »

Welcome Jeff!

I suspect that you bought that NST used, maybe off eBay or some other online forum. Which means you have no idea how it was used before you bought it. I bet that someone else had it immersed in an oil bath, and when you let it sit for a few months, some of the residual oil inside dribbled out.

The best way to figure out if there is any issue with the transformer, is to just fire it up again. I doubt that the oil leaking out is going to have affected its performance at all, as my understanding is that NSTs are typically potted with black sticky stuff that you have to get very hot before it will start to melt. Per some of Richard Hulls previous posts on depotting NSTs.

Fire up the NST and see if it works. I suspect it will work just fine.

As far as x-rays, well you are going to make copious amounts of them in any fusor type setup. The good and bad news is that with an NST the x-rays will be very low energy (<15keV) which is good, because it means they are less dangerous, but the bad news is that most detectors won't even be able to detect such low energy x-rays. Most detectors start seeing xrays at about 15keV and above. That is about where a standard geiger counter pancake probe starts picking them up. I don't know whether any of those low energy x-rays got through the glass of your MAKE fusor. I suspect that some of them probably did. It also depends on what kind of glass and how thick it is. Some materials are better transmitters of xrays than others.

Your exposure will mostly be determined by 1) how high you ran up the voltage on the NST with your variac, and 2) whether or not you had a full wave rectified setup, or a half wave rectified one, and 3) how close you were to your fusor when you were looking at it and how long it was running. Higher voltage == worse. Full wave rectified == worse. Closer == worse. Longer == worse. Hopefully you didn't have a full wave rectified setup, that you were running at 100% of the variac output, while looking at it from 6 inches away for several hours...

If you only had a half wave rectified setup, then your max voltage was only 7500V which means the max xray you could have made is 7.5keV, and if you didn't run the driving variac all the way up to its max, then it was even less than that.

What's done is done, and your exposure whatever it was is now baked in. You are still alive, have no cataracts yet, and it is what it is.

The best thing you can do, is make sure you understand the x-ray risks going forward, and protect against them. If your chamber is stainless, then you only have to worry about xrays going through the metal at >30kV on your power supply. If you go much above that, then you need to encase your fusor in lead sheet. If you are going above 10kV, then you should make sure you get some leaded glass to cover your viewport, as xrays will pour out of that even at 15kV. If I were you I would get leaded glass to cover your viewport for ANY voltage you run. Just use leaded glass. It is scary when you put a pancake probe up to your viewport at 20kV applied, and listen to your meter scream. Then you put the same probe up to the same viewport behind a piece of leaded glass, and you get mostly silence. Just background from elsewhere at 30-45 cpm.

Leaded xray glass is good. Use it.

The MAKE setup is not a good one for xrays, as the walls of the chamber are non leaded glass. Which meeans there is little to no shielding of any xrays. The MAKE setup is also not good safety wise, because it is not enclosed in a wire cage - like most glass bell jars are - and so it is also an implosion risk. I would be more worried about getting glass shards in my eye from an imploded MAKE chamber, than from low energy x-ray exposure.

Although your picture was not of the pump, and the text on the pump is therefore not clear, it looks like when you built the MAKE setup, you also bought a single stage vacuum pump. (It looks like it says Single Stage Vacuum Pump on the side of the pump.) Do the MAKE build instructions tell you to get a single stage pump? Is your pump single stage? If so that is very unfortunate, because for probably $50 or less extra cash, you could have gotten a 2 stage mechanical pump that will pull down to 4 microns, which is low enough to do fusion with a single pump setup.

I would suggest that you investigate building a KF based fusor with the Kozyvacu 2 stage TA500 pump, if you want to do fusion on a budget.

I am writing a thread about building one now here: viewtopic.php?t=15444

Joe.
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Dennis P Brown
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Re: NST Troubles & X-ray Protection

Post by Dennis P Brown »

I will only add that a NST will never hold a 15 kV voltage during operation with a plasma. This is a near short condition and a NST drops its voltage rapidly under those conditions - if you want to check this, measure the voltage under real operational conditions (Richard did this and use to have a thread on this very topic.) So, your exposure to x-rays was extremely small.
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Ryan Ginter
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Re: NST Troubles & X-ray Protection

Post by Ryan Ginter »

Along with the voltage sag Dennis has noted, the single stage pump may also have been a blessing in disguise. The higher the pressure in the chamber, the lower the speed electrons will reach while accelerating away from the grid.

Have any users on the forum actually measured X-ray emissions during glow discharge mode?
JoeBallantyne
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Re: NST Troubles & X-ray Protection

Post by JoeBallantyne »

Well, I didn't actually keep track of any numbers, but I most certainly did do the test I spoke of in my earlier post, where at 20kV or so applied voltage on the cathode with a plasma lit up, I stuck a 2" pancake probe directly in front of the viewport on my fusor, and the meter started counting like mad. Continuous stream of beaps, and the meter went off scale. I don't remember checking if it went off scale on every decade, but the counts were high enough that I decided there was NO WAY I was going to not have a piece of leaded glass covering the viewport.

The counts you get will be directly proportional to the current you are pushing through the fusor. The more current, the more x-rays, as the vast majority of the electrons that get accelerated and hit the anode are going to spit out a photon proportional to their energy upon impact. It takes 6.25e18 electrons to give you an amp, so 10mA is 6.25e16 electrons. Which generate basically that many photons on impact - that's a lot of xrays.

Not something you want to mess around with.

Joe.
Ryan Ginter
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Re: NST Troubles & X-ray Protection

Post by Ryan Ginter »

Since you say you didn't track any numbers, I'm guessing you don't remember what the chamber pressure was at the time. Do you remember any visual characteristics of the plasma? I would expect X-ray production in glow-discharge mode to be lower than in star mode. The chamber pressure will have a large impact on X-ray energy. More collisions with air molecules will result in a lower final velocity when producing bremsstrahlung radiation. The emissions range from zero at atmospheric pressure and increase in magnitude as pressure decreases, but I am uncertain at which point it becomes a concern.

Most Make Magazine style fusors use single stage HVAC pumps connected to chambers with plastic components, silicone seals, and vinyl tubing. I would imagine they have very poor vacuum performance.
Last edited by Ryan Ginter on Thu Jun 06, 2024 7:35 pm, edited 1 time in total.
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Richard Hull
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Re: NST Troubles & X-ray Protection

Post by Richard Hull »

All older neon transformers of the two knob ended ones are cast into the case with plain old molten asphaltum.

Oddly for those who say I use to have a post on the dip in Neon voltages, I found it instantly in the high voltage FAQs forum. Read the
FAQs!!

viewtopic.php?t=10333

Richard Hull
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Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
JoeBallantyne
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Re: NST Troubles & X-ray Protection

Post by JoeBallantyne »

Ryan - the fusor I ran that pancake probe experiment on with a plasma lit up at 20kV on the cathode was most likely at 12-17 microns pressure. On that fusor, any pressure less than 12 microns or so, and the plasma goes out at 20kV, and with more than 17 microns or so, and the current gets so high my power supply shuts down.

While varying the pressure in the chamber will definitely change the frequency distribution of the fusor's photon output (UV, x-ray, and for very high voltage fusors gamma ray), IMO to some degree, that change in photon frequency distribution is irrelevant. I don't really care how many more x-rays star mode produces than glow discharge mode. The reality is that there is a plasma lit up in both cases, and there is bremsstrahlung x-ray production both in the plasma, and when electrons are accelerated from the plasma or the cathode to the anode.

The bottom line is that fusors can and do produce dangerous levels of xrays, and the best practice is to just shield for them.

Period.

Joe.
JoeBallantyne
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Re: NST Troubles & X-ray Protection

Post by JoeBallantyne »

Now, I will say that I agree that most MAKE fusors likely have an atrocious level of vacuum (possibly hundreds of microns), based on what most of the pictures of the plasma in them look like. (Where the plasma is mostly lit up right around the wires themselves, and is not even centered in the cathode.)

Furthermore, if the builders followed what the MAKE article says to do, they only built a half wave rectifier. So if they use a 15kV NST, the absolute maximum voltage output is 7.5kV, and if they use a 12kV NST as specified in the article, then that max goes down to 6kV.

At very high pressures the NST is very much going to be current limited, and running at significantly reduced voltage output. Which means possibly that the most energetic x-rays a MAKE fusor with bad vacuum can produce is something on the order of 2 to 5 keV. But the current is going to be pegged at 30mA or so. So there will be lots of low energy x-rays produced. How many of those get through the glass, and how dangerous it is, I can't say.

The MAKE article at least tells the builders to not run their machines for more than a couple minutes at a time. Mostly probably to limit implosion risk.

Joe.
Ryan Ginter
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Re: NST Troubles & X-ray Protection

Post by Ryan Ginter »

I didn't mean to suggest all caution should be cast aside. I find it doubtful that the typical demo fusor could produce significant radiation aside from UV, but as you've said, shielding is always the best practice. If anything, the operation time of a demo fusor should be limited to reduce UV exposure. Anyone looking to experiment with high voltage in a vacuum should at a minimum possess a mica windowed Geiger counter.

As far as the 2 to 5 KeV X-rays go, it is my understanding that clothing and the dead layer of skin outside the body is enough attenuate most of them before reaching the living cells beneath. I suppose the eyes could be at risk but the glass of the fusor should do a fairly good job of stopping them. X-rays below 5 KeV are also fully attenuated after traveling through one meter of air, but even at a distance of one foot they are reduced by around 75%, and nearly by 100% for 1-4 KeV.

Of course, all of this only applies to the Make Magazine style fusors. Any more serious endeavor will pose a radiation risk. In such a device, the power supply becomes the primary factor for the intensity of radiation produced. A fusor will never produce gamma rays via bremsstrahlung though. While most graphics commonly describe a transition between X and gamma rays as frequency increases, X-rays do not transition into gamma rays. Both are the same type of particle and can occupy the same energies, the only differentiation between the two is the source. Gamma rays originate from the nucleus or annihilation events.
JoeBallantyne
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Re: NST Troubles & X-ray Protection

Post by JoeBallantyne »

If you are running a fusor at over 100kV, then you will produce photons with energies in eV up to whatever voltage you are using.

What do you call a photon with an energy of more than 100keV?

Is there some name other than gamma ray?

Maybe there is, but I don't know what it is.

I understand that normally radiation that is emitted from the nucleus is called gamma radiation, but my understanding is that it is not incorrect to call any photons with an energy higher than 100keV gamma rays.

They aren't x-rays at that point, because 100keV is the nominal upper bound on x-ray energy.

I'm pretty sure that a 200kV fusor is going to make both x-rays and gamma rays.

IMO it is definitely somewhat confusing that we have all these different names for different frequency bands of light.

But we do. Lots and lots of them. If you include names of colors there are probably hundreds of names of light frequency bands.

They just be photons. All of em.

Joe.
Last edited by JoeBallantyne on Fri Jun 07, 2024 12:46 am, edited 3 times in total.
Ryan Ginter
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Re: NST Troubles & X-ray Protection

Post by Ryan Ginter »

Above 100 KeV they are generally referred to as High-energy X-rays. I agree that the naming conventions are somewhat pointless, especially when improper use is the common practice. They are the same particle in the end, so it really doesn't matter.
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Dennis P Brown
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Re: NST Troubles & X-ray Protection

Post by Dennis P Brown »

The difference between a Gamma Ray and X-ray is not really energy (through there is a difference - X-ray's have an absolute limit, Gamma's really don't except in extreme (many GeV) and even that theoretical limit has been possibly exceeded.) The definition is how they are produced. Gamma Rays are solely produced via nuclear process's - commonly via a nucleus transition (through not solely via that methodology.) X-ray's are solely produced via electrons - generally from inner electron orbital/shells.

When it comes to radiation, best to error on the side of caution. In a fusor (yes, metal walls, avoid the window port, distance) I've tended to agree with those here that consider above 25 kV as a region to get serious about extra shielding (through again, error on side of caution); above 30 kV very concerned and certainly shielding is always a good idea for any fusor. But above 15 kV, as Joe points out, time to use detectors for certain.
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Jeff Duncan
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Re: NST Troubles & X-ray Protection

Post by Jeff Duncan »

Hey guys.

Thank you all so much for your input. The activity and consideration in this forum is something I'm very appreciative of. It's good to hear that, for the most part, my exposure to X-rays was minimal. I'll definitely use this lesson in the future to always protect myself properly.

Mr. Ballantyne,

Your assumption regarding my vacuum pump is correct, as it is a single-stage. I'm taking a look at the link you provided. Fusion on a low budget has always been my goal, considering I'm in high school and my funds are limited. Additionally, the

Thank you,
Jeff.
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