Beryllium

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Beryllium

Postby lutzhoffman » Fri Jul 30, 2010 2:29 am

Beryllium Be

I have always been fascinated by the worlds lightest practical metal, I say practical because Lithium reacts with the O2, and the N2, in the atmosphere, which renders it useless for most practical applications. Beryllium is also quite heat resistant, and very strong, with a melting point close to steel. Toxicity is a major problem which restricts the use of Be to those applications which do not require grinding, filing, sanding, or welding unless you are very very careful, with respirators, disposable glove boxes etc.

Beryllium in bulk metal form can be handled with similar precautions as lead, cadmium, or other toxic metals, although some sensitive to it will develop a skin reaction, similar to an allergic reaction. For the rest of us a simple hand washing is fine, on the plus side it does not accumulate in the body forever, and it will over time be eliminated from your body in sub toxic amounts.

Now to the fun part, what is it good for? Where do I start? One interesting property is its transparency to X-rays, you could almost think of Be as a block of X-ray glass. An example is a 1/8" thick Be sheet will barely be visible, with just a feint outline on an x-ray image set for the same settings as a finger or a hand, increase the energy just a little and it disappears from the image.

This brings us to a major use of Be, which is radiation windows. With its high strength, a Be window capable of withstanding even a full vacuum, will transmit X-rays down to 1KV, this makes it perfect for X-ray spectroscopy, and soft X-ray tube windows. Be also makes a great window material for high speed electrons. If you enclose a scintillator with Be, then you can exclude the light from the PMT, while still transmitting soft X-rays, and even low energy betas. Be is one of the few materials that can make a window thin enough to allow for the detection of Tritium beta radiation, which even mica window GM tubes normally fail to to detect. Thus if a Be window is added to a device like a fusor for example, then it will create a spectroscopic window which can be used to probe what is going on inside with the right detection equipment.

Since fabrication of Be into various shapes presents a problem for the home workshop, we are ofter reduced to buying a Be item which is a close general match, to the desired shape and thickness. Be windows from .5 to 1mm thickness can be had from old mammography tubes, and some other Be window X-ray tubes, like diffraction tubes - Which often contain 4 Be windows for each tube. Another neat source of very thin Be for use in fabrication radiation windows is the new Beryllium Tweeter speakers. These cost a bundle new, but they are very thin, and their dome shape can be taken advantage of for vacuum use. To mount the Be window into your fabricated form, you can use epoxy. I have had pretty good luck with slow setting aluminum filled metal bonding epoxy. Just clean the Be first with acetone, or with some other good solvent like MEK etc. Ebay is a great place to look for Be, it shows up often.

The nuclear properties of Be also make it very interesting, hit it with just about any accelerated ion species with enough energy, and lots of neutrons are liberated, which is why Be is the most common neutron producing target at above 1 Mev. This is not to say that nothing happens below this. With deutrons, even at 500KV, a Be target will produce 10E7 Neutrons per second per micro-amp. Drop the deutron energy to about 250KV and you still get 10E6 N/Sec. The worlds first visible amount of Pu239, was made by bombarding Uranyl Nitrate with Neutrons, produces from a cyclotron accelerated He++ plus Be reaction. The chemical properties of Pu were determined from these experiments, which was an amazing feat of micro chemistry with a milligram quantity.

Mixing just about any alpha source with Be, will give you neutrons. The amount is small like one Neutron for every 10-20K alphas when using radium, with an average alpha energy of 5.5 Mev. Today Am-241 (which is used in smoke detectors) has largely replaced Ra-226, mainly due to the annoying high energy betas, and gammas from Ra-226, and its extreme toxicity. Am-241 only has one low energy 59Kev gamma line, which can be filtered out with only 1/16" sheet lead, or even 1/8" inch of copper. Ideally the alpha emitter should be intimately mixed with the Be powder, but in reality this is not needed. A thin layer of Am-241 directly against a Be plate will give you significant neutron production, in a way much safer way than that nasty bone seeker Ra-226. Yes Am-241 goes to the bones also, but at least some is eliminated, and for other reasons of biology, its not quite as bad. So now you finally have a way to test that He3 tube that you scored on ebay, just collect some old smoke detectors, but remember do not take them apart since that's against the law : ) Overall Be is very interesting and a very useful metal, although with limited options for home shop fabrication. For some applications there simply is no substitute.*

*Just for reference tight weave graphite epoxy composite is also being used for detector windows, while not nearly as good as Be, it will do for many applications like low energy gamma, and X-ray detector window use, like in imaging.
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Re: Beryllium

Postby Doug Coulter » Fri Jul 30, 2010 10:36 am

We have managed to acquire some Be here from sources such as you mention, in various form factors. Most useful to us so far has been some fairly thin foil, about 4 mils thick.
Though Be is about as brittle as it gets, with care you can cut this stuff with scissors without breaking it, and it's what we use for neutron generators, with the source from
a staticmaster brush. These don't last as long as you might like, but for sheer "loud" they are hard to beat when new. A staticmaster source has the radioactive part as a thin film over
an piece of Al, and is just stuck on there with double sided tape adhesive, so it's easy to remove and have intimate contact with the little piece of Be. Air space means any alphas are losing energy to the air fast, so
having them touching is a fairly big deal. The way we build ours, a normal geiger counter doesn't see any other form of radiation coming through, only neutron detectors show that it's anything but an
inert chunk of stuff, as the Be foil is a little larger than the source and shields all it's other output. These are not very loud neutron sources, but enough to put some bubbles into a BTI if
left there overnight. We can count them some on our 3He setup as well, even though we have that setup with a high threshold to make it "numb" enough for use with an audio amp at full fusor outputs.
Our first staticmaster-Be source was simply a Be foil placed over the source in an unmodified brush source, and held on with scotch tape so we could easily turn it on and off.

Most machining of Be is done by grinding it -- and as Lutz says, that's for someone either really dumb, or very well equipped -- this stuff is really toxic, and particularly damages lung function, in some cases all too permanently. I did get tasked to sand some thinner while working at a local college (back in the '60s), and survived it, but maybe I was lucky? With what I know now, I sure wouldn't put it on a grinder in my shop.
The stuff is so brittle I'd not dream of handling it any other way -- a normal machine operation would just result in breaking it.

As Lutz points out, another use of it is for X ray windows, where it doesn't cause much loss that would "smear" lines on a spectrometer. We have a somewhat thicker piece of Be I may put over a hole in a flange so we can do spectra of the fusor outputs better. According to Kohl, Be is really tough to hard-join -- few things wet it without making even more brittle intermetallics, so brazing tends not to work, nor does welding in most cases. The basic brittleness and the fact that just about any two things don't have matching tempcos is a recipe for failure if the joint has nothing that can flex. Having said that, I have had fairly decent luck gluing smaller, thinner pieces with epoxy with a fairly low failure rate. Those pieces I was tasked to sand thinner were then glued over a hole in a glass pipe for an X ray pinch experiment, and they made a fine vacuum seal that let the X rays out.

Here's a pic of some sources we made here for detector testing. They can be "turned off" by removing the Be foil. I just milled a channel into some plexiglass to protect the guts from human contact, and threaded the back end so we could mount them in jigs with reliable placing.
Attachments
NSources.jpg
Pic of neutron sources
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Beryllium

Postby Jerry » Sat Jul 31, 2010 1:40 am

This stuff is way worse than lead. I woudnt be caught dead machining it. Its not the same as beryllium copper which is not too bad, toxicity wise.

http://en.wikipedia.org/wiki/Berylliosis

Here is an article on American Machinist about machining it:

http://www.americanmachinist.com/Classe ... SKEY=Issue
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Re: Beryllium

Postby Doug Coulter » Sat Jul 31, 2010 12:54 pm

Well, I and a lot of others work with lead all the time and no troubles. In reloading, you get more lead in you from cleaning brass than from melting and casting bullets -- lots more, from the lead compounds in the primers that get on the brass (which are easier to assimilate organically in the bargain). This has been tested when a reloader wound up with high lead levels -- it was his brass tumbler that was the source, not his bullet casting bench! I machine lead alloys, no problems there, the swarf just falls down in the ways, and I clean it up and send it to the bullet making bench for reuse -- as a metal, it doesn't get inside you easily or easily become part of you if it does. Lead acetate will, though. Or other lead compounds that are soluble.

This stuff IS way worse, but....I've lived through working it a good bit, just by being normally careful, as I am when grinding quartz on my lathe -- you keep the dust down! I use coolant so it winds up as mud that is easily wiped off later. And you don't stand there on axis inhaling it either. Common sense with any material, because even inert stuff like quartz dust will get you in the end (Silicosis). So far, zinc fume from careless welding is the only thing that has gotten to me here -- and I learned my lesson on that quick, it's not fun at all. Like having the flu, but all rolled into a couple of hours of extreme misery. At least it wears off, though, with little lasting bad effect. I also avoid breathing graphite dust when I machine that -- black lung is black lung even if it isn't from being a coal miner.

You don't want to be a mouth-breather around most things -- we have a nose for a reason and it really does a good job catching stuff in the air before it gets way into you -- so blowing your nose after working some things is a really good idea, and lets you know if you're somehow getting a lot in you -- so you can improve your other technique.

I am surprised anyone machines this stuff, not because it's toxic -- after all, there are those who machine Pu (with precautions of course, like inert atmosphere and remote control), but because all the samples I've gotten are so grossly crystallized that they snap between the fingers. I would suppose that some new technique in casting/alloying to prevent that has come about to allow that. If you look closely at the picture in my previous post you can see the crystals in a sample we got on ebay.
I've seen almost 1/4" thick pieces of Be snapped in my fingers. The stuff is very fragile, and makes quartz look elastic by comparison.

Although we don't need to be sued for our advice, personally I'd say most of that stuff "known to the state of California to cause X" is a little over the top, an excuse to not have to have common sense. (as is evidenced by other events there -- there is a distinct lack of sense in that population)

My Dad, who lived to a ripe old age had no such "protections" and used carbon tet extensively as a cleaner and flux remover when he was a technician, before he graduated to TCE! Now you can hardly buy the stuff.

I think in most cases "if it's not food, don't eat it" and "if it's not air, don't breathe it" works out fine as a rule. "Wash your hands, man!" And don't smoke when there are flourocarbon vapors in the air -- you wind up breathing elemental fluorine in that case. I would also say that the rules could be different for a hobbyist who may work with something a couple times in a lifetime, and someone who does it day in and day out. Some things accumulate with repeated small exposures, and you have to be tons more careful if you're making a career of working with them.

You want to talk nasty -- hexavalent chromium for hard chrome plating (Cr2O3 + H2SO4)....now THAT is evil, and it even looks like blood in the plating bath. I do that in a fume hood, you bet.
Even there, I use an anti-misting layer of oil and floating balls on the surface to keep the misting down, and just don't do it much, either -- it even destroys fume hoods from the inside out. That stuff stains you, then burns you, then gives you cancer.

I'd have to say it's my personal version of an evil substance, on a level with methyl mercury. At least it won't go through nitrile gloves easily.

Another one to avoid is the fumes from nitric acid and reactions with it. Unlike say, chlorine or ammonia, it doesn't irritate you quickly so you get out of the place instinctively before much damage is done, it doesn't even smell bad. But you wind up coughing up nitrated lung tissue for days if you inhale even a CC of that stuff -- avoid!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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