Author Topic: X-ray with tesla coil  (Read 208 times)

Offline Tardief

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X-ray with tesla coil
« on: June 28, 2019, 10:08:29 AM »
Hi,

Is it possible. To produce X-ray with a  tesla coil and neon tube? I am a bit concered about it. There is vacuum in it and plenty of space to accelerate the electrons.
What do you think?

Offline Mads Barnkob

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Re: X-ray with tesla coil
« Reply #1 on: June 28, 2019, 10:49:25 AM »
One of the best and most thorough guides on the dangers of Tesla coils is the list on pupman: https://www.pupman.com/safety.htm

Quote
5.0) Ultraviolet Light and X-ray Production

Ultraviolet light may be produced by the spark gap during operation of a tesla coil. The human eye has no pain sensors within it, so the bioeffects are felt later, when it is too late. (Ever look at the sun for a while, or watch a welder at work?) The light produced in a spark gap is essentially identical to that produced by an arc welder, containing substantial amounts of hard ultraviolet light. As any professional arc welder will tell you "Don't Look At The Arc!" Spark gaps produce a large amount of UV and visible light. The visible light is extremely bright, and the ultraviolet light will damage your eyes, and can cause skin cancer. The arc is so bright that you couldn't make out any detail anyway, so why bother? If you must study your spark gap, use welder's glasses. Generally, it is not too difficult to rig up a piece of plastic, cardboard, etc. that will shield yourself and others.

X-rays

X-rays can be produced whenever there is a high voltage present. Although a number of coilers have tested their coils for x-ray radiation and found none present that is not to say that x-rays cannot be produced, especially if vacuum tubes, light bulbs, and other evacuated vessels are placed near a coil. Here is a little information about X-rays.

X-ray Production

A number of vacuum tubes work pretty well as X-ray tubes, and several articles have appeared in Scientific American magazine in the distant past. X-rays are typically produced by slamming electrons into either the nuclei or inner shell electrons of atoms. The source electrons are usually boiled off a heated filament (cathode), and accelerated toward an anode via some large potential difference, typically 25-150 kV in the medical world. Basically, any time the voltage gets above 10 kV, there is a significant risk of X-ray production, and the risk increases with increasing voltages. You can also get some X-ray production via field emission, whereby electrons escape a cold metal due to very high local electric fields (the Schottky effect). This was probably the type of emission obtained by an amateur described recently on the list. For the remainder of this discussion I will limit my comments to conventional X-ray tubes, using a filament and anode, although most of it applies to both forms. The target or anode is normally a high atomic number material like tungsten. X-ray production is relatively inefficient, so most of the energy is wasted as heat (typically about 99% with good X-ray tubes). Tungsten works well because of its high melting point (to absorb all that wasted heat energy). If the potential difference between the anode and cathode is +100 kV D.C., a spectrum of X-rays will be produced with energies from zero to 100 keV. The graph of the number of X-rays produced (y-axis) versus X-ray energy (x-axis) has a negative slope with a Y=0 point at x = 100 keV. Hence, many more low energy X-rays are produced than high energy X-rays. Some of these low energy photons are absorbed by the tube housing. In a clinical X-ray machine, the tube is placed in a leaded shield with a window (hole) in it for the X-rays to escape through. This window has a piece of aluminum over it to further attenuate the low energy X-rays. In conventional equipment, the tube, housing and aluminum filter accounts for about 2.5 - 3.5 mm of aluminum equivalent material in the exit port. This effectively knocks out most of the low energy (<10 keV) radiation, which would be absorbed in the patient and could not contribute to producing an image anyway.

X-ray Absorption

High atomic number materials readily absorb x-ray radiation. There is an energy dependence here, as high energy X-rays are more penetrating than low energy x-rays. For example, the percentage of radiation which will pass through 10 cm (about 4 inches) of water is 0.04% at 20 keV, 10% at 50 keV and 18% at 100 keV. Compare this with 1 mm of lead (about 0.04 inches), which transmits 0.02% at 50 keV and 0.14% at 100 keV. The human body absorbs X-rays pretty readily (similar to water), but becomes more transparent as the energy of the X-ray increases. That is why we use 50-150 keV for many clinical procedures. The low energy X-rays are filtered out of the spectrum before they enter the patient, usually through the use of an aluminum filter, which lets the high energy X-rays pass through with little attenuation (except possibly to give you enough contrast to see what you want). Most of the x-rays are absorbed in the patient, with 1-5% exiting the patient typically. Low energy X-rays (0-15 keV) are totally absorbed in human skin near the skin surface, and would contribute substantially to patient dose if allowed to reach the patient. This is to be avoided in general!

Shielding

The best material is lead. Concrete and steel also work pretty well. Aluminum is a poor absorber of radiation, unless the radiation is very low in energy. Most plastics are similar to water in attenuating properties (quite poor).

Hazards

X-rays are capable of producing ionizations, which means that the electrons can be stripped off of atoms when an x-ray is absorbed in a material. This results in the production of chemically reactive free radicals, and the direct disruption of chemical bonds. This is generally bad in humans, causing cancer, leukemia cataracts, etc. However, due to natural background radiation levels, humans have built in radiation repair mechanisms and can handle low doses of radiation quite well. Bio-effects are not generally observed for doses of less than 25 rem. Skin reddening occurs with doses of around 300 rem or so. Natural background radiation levels typically contribute 0.2 - 0.5 rem per year. Most regulatory agencies recommend no more than 0.5 rem per year above background radiation levels for the general public. Occupational radiation workers can get 5 rem per year above background. The radiation from a well designed X-ray tube can be as high as 10-50 rem per minute of exposure, at a distance of 1/2 meter. The radiation source acts like a light bulb, decreasing in intensity via the square law with distance. Hence, don't stand close to a possible radiation source, use adequate shielding and minimize the exposure time. Incidentally produced radiation from metal objects other than X-ray tubes will generally be at much lower production levels, but should be avoided, nonetheless.

Regulations

In the U.S. the individual states regulate X-ray machines. They generally keep close tabs on clinical and industrial X-ray machines and aren't too impressed to see them in the hands of people without the appropriate licenses. If you happen across an old X-ray tube, you might consider releasing the high vacuum inside (very carefully, please) so that it is inoperable, and a little safer to handle for show and tell (and much more acceptable to the regulators). This can be done by making a small hole in the glass envelope with a file, keeping the tube wrapped in a large quantity of towels for implosion protection during the process. (It goes without saying that you should always have your favorite towel handy anyway [for you Doug Adams fans]).

Monitoring

At this point I presume you are wondering how to tell if that great apparatus in your basement or garage is producing X-rays. There are several ways to tell. First, go look for a surplus Geiger-Mueller counter at your local hamfest or make friends with someone in your local fire department, since many fire departments have radiation survey meters at their stations (in case we have a nearby nuclear explosion, etc.). (Don't bother with the fire department if your apparatus is likely to upset them!) In addition, nearly every hospital has a radiation safety officer who is likely to be more than willing to take a look at your toys, and will bring a radiation survey meter along. The standard method for monitoring radiation dose is via film badge and/or thermoluminescent dosimetry monitors, but these are not all that useful to the experimenter since they must be mailed back to the dosimetry lab for reading. In general, film is quite insensitive to radiation, and is of limited value in the experimenters setting unless you can leave the equipment on for a long time to get adequate exposure. Cloud chambers are great fun and can detect a variety of radiation particles, but get easily overwhelmed by devices that put out even low radiation levels. If you don't expect any radiation but still want to check, a cloud chamber can be used. Buy a thorium doped lantern mantle at your local camping store to use as a radiation check source to make sure your chamber is working okay before you power up your equipment. Another possibility is to construct an electroscope and place it near your apparatus. An electroscope measures the amount of charge using two thin metal foils which are charged up to a high potential, causing them to swing apart due to repulsion of like charges. Radiation ionizes the air in the electroscope chamber, causing a loss of charge on the foils. Naturally, this type of equipment has limited utility in the direct vicinity of high voltage equipment if electric fields are significant.

X-rays and Tesla Coils

I have monitored my various tesla coils using a number of different radiation instruments and have not seen measurable radiation levels. My coils produce 3 to 5 foot sparks in magnifier and conventional forms using up to 15 kV input, with power levels of no more than 1.5 kVA. Obviously, you don't want to get a survey meter too close to an operating tesla coil.

Finally, always keep safety in mind with all of this equipment. Humans are not able to sense X-ray and ultraviolet radiation. If you think you are producing some, use an appropriate instrument to find out for sure.

 
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Re: X-ray with tesla coil
« Reply #1 on: June 28, 2019, 10:49:25 AM »

 


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