Trying to develop an X-ray generator using a pyroelectric crystal, for less than 100$
Ok, so things so far have been going exactly as I figured......that is painully slow.
I received the vacuum pump and as luck would have it, it's a total piece of garbage.
The vacuum gauge on it when it came looke like it had a rough life, so I had to replace it. Turns out that a vacuum gauge witht he correct scale is kind of hard to get in my country. Only 1 or 2 online shops that have it in stock.
This is how the original gauge looked. No glass on it and the indicator needle buggered off to some better place.
This is the pump I got. It's from ITE (german-chineseium grade vacuum pump, from what I can gather from the datasheet) and it's a Blue-Tec MK-60.
Here's the specs on it
So after about a week, the new vacuum gauge came and lowe and behold....it was nothing like the description.
On the left is the gauge from the store's pic. On the right is the very one that I got. But, ignoring my frustration, at least I was closer to testing my pump.
The next thing that got in my way of firing up the pump was a lack of proper fittings. After being delayed 1 week because of my half-arsery and ordering the wrong kind of fitting (Ordered by mistake a 1/8 NPT fitting instead of a 1/4 NPT), when I actually got to order the right one, it never came. No one phoned me to say if they have it in stock or not, no mails, no nothing.
Because my frustration grew eve more, I decided to go at it caveman style and plug the pump's inlet with what I hoped to be and airtight seal made from a small round piece of rubber gasket, wide enought to cover the 1/4 hole of the fitting.
And, of course, when you're on a roll, why stop, right? Turns out that the vacuum pump doesn't go all the way down to the specified vacuum.
I bought some vacuum pump oil and flushed the pump twice (the old oil was OK, but it looked more like motor oil than vacuum pump oil) but still it only went down to about 250 mbar, which is way more that the required 0.05 mbar. Also, the oil that came with the pump had some grime in it, probably because the pump inlet was left open in a shop somewhere.
So, as of now, I either have a leak in the system (probably the rubber is not sealing well) or the pump is actually FUBAR from being run with the wrong kind of oil and/or because of debris still inside it. I can only verify this by actually putting a 1/8 NPT plug on the inlet and running it like that but alas. these seem to be as rare as hen's teeth.
To be continued.....
I haven't done any work on this because I'm stuck looking for a suitable vacuum pump that doesn't cost an arm and a leg.
The vacuum level isn't that high, but most chinesium-grade pumps I've seen don't look that promising.
I may have found one that fits the bill, both in price and performance. It's a second hand, 2 stage pump. Hope it also works. Sometime next week I'll find out if this is really the case or I just threw away 50 Euros.
I've also been thinking about the set-up and fittings I'm going to use. I basically want a set-up that's easy to disassemble and also holds a vacuum. Kind of much for them, but I'll test this out once I have the pump (if it works)
To get the for factor as small as possible, the only way to go, as far as I've seen or read is by using a pyroelectric crystal. This has the advantage of taking up a few cubic centimeters of space and uses voltages somewhere between 5 and 12 V. Perfect!
Ok, so what is a pyroelectric crystlal, I hear you ask? Well, it's a crystal (most common ones are Lithium Niobate or Lithium Tantalate) that when subjected to a temperature differential, charges inside the crystal matrix start wandering about and elctrons wil be emmited from the Z-plane of the crystal matrix. In other words, you heat up the crystal from the bottom, for example, electrons gather to the top of the crystal and will be emitted outwards. Without any additional acceleration voltage.
If you don't believe me, (and it's understandable, because I didn't until I tried it) here's a scope shot of a quick experiment I did.
The set-up is pretty simple. I took a slither of Lithium Niobate crystal, hooked one end to the ground of a scope and I left the the top of it floating near the positive of the scope's input (just a straight BNC cable, attenuation X1).
Whenever the crystal was exposed toa temperature differential, electrons started spewing from it and would appear on the scope as soem very narrow pulses. The slither was heated using a regulat heat gun, set to about 100 degrees C. A few 2 second shots of hot air on the crystal generated the scope shot you see.
Now, please take into account that what I've done here is just proof of concept (for myself at least) to see if I have something tangible here.
As you can see from the scope shot, a lot of pulses show up, so tht means that indeed, electrons do indeed escape from the crystal. No, these are not X-rays. At least not yet. These are just run of the mill electrons :D. For the actual X-rays, a few more things are needed.
Also, bear in mind that electrons are only emitted when the crystal has a tempeerature differential across it. Once the crystal uniformly heats up, there are no more emmisions from it.
Ok, so now that I have some proof that I'm not just chasing green unicorns, I can get on to bigger and better things.
X-rays are actually generated when an electron collides with another material (i.e. the atoms inside that material). So, basically, if I take the slither of crystal and put it in a medium where electrons can travel unimpeeded (say, in a vacuum) then have those electrons slam into something, X-rays will be genrated.
Granted, those will be some very low energy X-rays, but hey.... if you want to go handheld, it's better than lugging a whole grandma's basket filled with tubes and tranformers.
What I want to do next is build a vacuum enclosure, stick the crystal in it , get some vaccum inside it then have a small window where X-rays can escape from.
I figured that aluminium foil, copper foil and mica are some good candidates for the window material.
I know it doesn't look like much, but hopefully those fittings are going to be my vacuum chamber. Why go for those, instead of a glass envelope? because I wnt to experiment with this, meaning I might want to try different crystal orientations and different window materials, therefore I want something that seals adequately under vacuum and can be easily taken apart. Will it really work ? I don;t have a clue, but I hope it does. All I can do i just hope and speculate, as at the moment I don't have a vacuum pump.
Speaking of vacuum, there seems to be a sweet spot for the vacuum level for this thing. That seems to be somewhere between 1-10 Pa of pressure (or 10^-2 to 10^-3 Torr). I'll try to aim for anything under 5 Pa, but as I'm a noob regarding this kind of stuff, again, I can only hoep for the best right...Read more »