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Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Many that did not die suffered other serious effects. Radiation burns leading to tissue necrosis or skin cancer, amputations, all sorts of nasty stuff. I believe it was one of Edison's glassblowers who tested x-ray tubes with his hands. Ended up having both hands amputated and still died. Many of this early equipment was not appreciably more powerful than a typical modern dental x-ray tube. You really can die or be severely disfigured by this stuff and by the time you know anything is wrong, it will be much too late. Think of a sunburn, arguably the most common type of radiation burn, the effects don't show up until hours after exposure. The difference with x-ray photons is that while UV from the sun is absorbed by the upper layers of skin, x-rays pass through the body and burn the tissue all the way through, blasting bits out of cell dna they happen to hit.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
James wrote ...
The difference with x-ray photons is that while UV from the sun is absorbed by the upper layers of skin, x-rays pass through the body and burn the tissue all the way through, blasting bits out of cell dna they happen to hit.
In fact, X-rays which pass through the body are much less dangerous than soft (low energy) X-rays, which are wholly absorbed, transferring all their energy into the tissues.
In diagnostic radiography, aluminium filters are employed to block these soft X-rays, which carry the greatest health risk, but contribute nothing to the image.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Yes, the absorption is what causes the damage, but even the soft x-rays penetrate much more deeply than UV photons. They are absorbed throughout the tissue rather than merely by the top layers.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
My father is a dentist and his clinic has an X-ray room. He said I can test my device there.
I planned to put my device in the room,turn it on and off using radio control.Will the room block radio wave?
Can a medical X-ray room provide proper Shielding?
Is the 2X2 vacuum tube really that dangerous?
Maybe I can take a few radiographs using my father's dental x-ray unit instead of building my own.The reason why I want to build my own is because dental X-ray unit seems only can take small pictures,smaller than a cell phone or other objects that is interesting to radiograph,and it is interesting to build homemade devices.
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
è¬æ˜•å“² wrote ...
My father is a dentist and his clinic has an X-ray room. He said I can test my device there.
I planned to put my device in the room,turn it on and off using radio control.Will the room block radio wave?
Can a medical X-ray room provide proper Shielding?
Is the 2X2 vacuum tube really that dangerous?
Maybe I can take a few radiographs using my father's dental x-ray unit instead of building my own.The reason why I want to build my own is because dental X-ray unit seems only can take small pictures,smaller than a cell phone or other objects that is interesting to radiograph,and it is interesting to build homemade devices.
It will probably block it, but you should shield it well anyway, better safe than sorry, and make sure you have a hardline to turn it off if need be, and yes, any x-ray tube can be dangerous, dosage accumulates over time.
I'd try using his first, if it works for what you want you can save yourself a lot of trouble.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
A vacuum rectifier tube is a really poor emitter of x-rays. Still potentially dangerous, but not nearly as much as a real x-ray tube I had assumed you were working with.
Dental x-ray machines are intended to image small objects, but the beam spreads just like a beam of visible light, so imaging larger objects is simply a matter of increasing the distance between the tube and subject and increasing the exposure time accordingly. An additional bonus is the greater the distance, the sharper the resulting image.
The nice thing about using a dental machine is they are very well shielded, and limited to about 70 kVp so scatter and leakage are minimal. My advice is to place the film cassette on the floor with the object you want to image on top of it, then point the tube straight down and take an exposure of a few seconds. If you are limited to shorter exposures, you can take several of them without moving anything and get the same result as a single longer exposure. If you want to experiment with radiography and have access to a dental system then this is the way to go. It may not be as exciting as building one yourself from scratch, but the results will be FAR better, and it is much safer being a properly constructed and certified apparatus.
You should be able to find a real x-ray film cassette with intensifying screens for under US$20 on ebay. There is a tradeoff between exposure time and image sharpness, with high speed stuff being less sharp and mammography offering the best quality, but pretty much anything will provide impressive results with practice. All silver halide film uses very similar chemistry, so you can develop x-ray film with ordinary photographic developer and fixer, and most can be handled under a red safelight.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
100kV sounds reasonable for a dental machine, but in practice it was probably operated at 60-70kVp. Usually the voltage is adjustable. For a larger general radiography machine utilizing a rotating anode tube, 300kVp is possible, but 100-125 kVp is much more typical. 300mA peak current is not too unusual.
Yes, a vacuum tube can emit dangerous amounts of x-rays. The dosage is cumulative, so while the output will be far lower than a proper Coolidge tube, you will have to run it longer to take a picture and your total dosage will be higher. Additionally they lack a proper target so radiation spews out from all sides instead of being mostly directed. Below 50kV you are unlikely to get much penetration, so you will need much longer exposure times for a given output. Additionally, the low voltage "soft" x-rays are heavily absorbed by tissue and are actually more damaging than those in the 60-80kV range. If you look closely at a dental x-ray head, there is an aluminum filter, usually 1.5mm thick to filter out most of the softer radiation.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
James wrote ...
Yes, a vacuum tube can emit dangerous amounts of x-rays. The dosage is cumulative, so while the output will be far lower than a proper Coolidge tube,
There are 'proper' Coolidge tubes like the legendary Svetlana transmission target BS7-W which is designed to operate between 3 kV - 15 kV at a maximum input of 20 mW. An inverted 2X2A - as in Radhu's recent experiments - has an output considerably greater than a BS-7, as you will see from my dosimetry notes in Radhu's X-ray thread.
James wrote ...
Below 50kV you are unlikely to get much penetration,
Much penetration of what, James? There is a great deal of X-ray imaging going on all the way down to the water window at 285–532 eV, part of a a big research migration to the Ultra-Soft kingdom below 5 keV.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Proud Mary wrote ...
James wrote ...
Yes, a vacuum tube can emit dangerous amounts of x-rays. The dosage is cumulative, so while the output will be far lower than a proper Coolidge tube,
There are 'proper' Coolidge tubes like the legendary Svetlana transmission target BS7-W which is designed to operate between 3 kV - 15 kV at a maximum input of 20 mW. An inverted 2X2A - as in Radhu's recent experiments - has an output considerably greater than a BS-7, as you will see from my dosimetry notes in Radhu's X-ray thread.
James wrote ...
Below 50kV you are unlikely to get much penetration,
Much penetration of what, James? There is a great deal of X-ray imaging going on all the way down to the water window at 285–532 eV, part of a a big research migration to the Ultra-Soft kingdom below 5 keV.
Here is a botanical study at 10 kV 8 seconds.
Ok, proper as in conventional medical diagnostic tubes, dental and general radiography, the sort that people usually think of when speaking of x-ray machines. Of course there are obscure exceptions.
Penetration of household objects, the sort of thing most people are likely to try imaging. Sure you can take pictures at lower voltages, but look around at the hobby radiography out there, most people are looking at things like cell phones, small appliances, light bulbs, clocks, pens, lighters and other things that image well in the 60-80kVp range using conventional and readily available medical imaging film and intensifiers. Certainly for any attempt at digital imagine you will need a fair bit of power. Even 4mA at 70 kVp is dim enough on a fast intensifier screen to need a long exposure with a sensitive camera.
It still remains true that a real x-ray tube designed for imaging will have a much smaller and more controlled focal spot than any vacuum rectifier I'm aware of. What use is a large emission if you have to block most of it with a collimator in order to get a sharp image? Yes I'm sure that with enough digging you can find some strange oddball tube that is technically a real x-ray tube that this statement does not apply to, but for the vast majority of cases it is true.
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Homemade X-ray machine question
