Beryllium
Posted: 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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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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