DISCLAIMER!!!: This project can be EXTREMELY dangerous if you do not know what you are doing, in the case of this system, the x-rays are really the least of the problem, assuming you have something to protect yourself with. However a flyback transformer can give you a nasty shock that could even kill you in some cases. The X-ray emission from this project is not dangerous if you understand the physics and protect yourself from it. Regardless, shielding is a necessity. I am NOT responsible for any damages to people or property if you attempt this.
This is an Instructable covering the first part of a project I have wanted to do for some time now. After watching various videos and studying up on how x-rays were produced and interacted with the world around them, I decided I would very much like to experiment with them, as I have a well vested interest in high energy physics and electronics. I did not wish to spend many hundreds of dollars or possibly thousands on a real x-ray setup, as I wanted to experiment now and wished to see if I could produce them cheaply, reliably, and repeatably with parts I already had or could very easily acquire.
As for background, X-rays are very high energy photons produced when an accelerated electron strikes something and returns to its ground state. So to produce them, you must accelerate electrons to an appropriate energy to release an x-ray. This energy is measured in electron volts, or eV. There are also two categories of x-rays that we will associate with; Soft x-rays, and hard x-rays. "Soft" or "Low energy" x-rays are produced at around 800 eV to 5 KeV, while so called "Hard" or "high energy" x-rays are produced at energies greater that 5 KeV, upwards to 100 KeV. Soft x-rays are produced by this project, and are unable to penetrate objects as well as hard x-rays, and are often absorbed in air or your object of study. Therefore they are not typically used for imaging, due to scattering and absorption. Hard x-rays can be absorbed or pass through different materials, and their different rates of attenuation can show images when projected at a screen sensitive to x-rays. Essentially like shining a light on something and creating a shadow, materials that attenuate hard x-rays more readily will show up white, as x-rays have not penetrated through that material and made it to your imager, Whilst when hard x-rays do penetrate through, they hit your imager and leave no shadow. The x-rays produced by this system will typically be absorbed in air or water due to their relatively low energy, and are not useful for imaging, however you can still measure these x-rays, and I will speak more of this in the other part of this project, the detector.
*soft x-rays can be considered much more dangerous due to their higher rates of absorption, so care must be taken, and shielding worn or placed between you and the emitter.*
So came the first component; the tube. I am an avid collector of different valves and interesting vacuum or gas filled electron tubes. It so happened that I had a High voltage beam triode, which when operated in a cold cathode configuration, meaning the cathode was not boiling off electrons due to thermionic emission, I could accelerate electrons to an appropriate High energy for x-ray production.
Step 1: The Source
My source is a High voltage beam triode from RCA, The 6BK4C 6EL4A. This tube is very well suited for this since it has; 1. A physically far apart Anode and Cathode, this will prevent arc out and degradation. 2. A well documented datasheet that states its level that it produces X-rays at. 3. It is robust, and simple.
There is one drawback to this particular tube, and that is that it is a revised version of a previous tube. It is a revision equipped with leaded glass to reduce x-ray emission. Nevertheless the stated production rate is somewhere in the neighbourhood of 2 rads per hour. The leaded glass will not prove to be a terrible hindrance, as the tube is quite active.
Step 2: The Power Supply
The tube isn't going to produce x-rays when it wants to, the electrons must be accelerated. To do this DIY I chose the trusty ZVS flyback driver. The ZVS, or zero voltage switching driver is a tried and trusted way to produce high voltages reliably and cheaply, you can read more about the circuit I used here https://www.instructables.com/id/ZVS-Driver/ as it has many many uses other than this.
After mucking about with the turn ratio on the primary and feedback winding and changing values of inductors, etc. I had reached an appropriate output voltage of 27,000 volts, My triode is stated to produce x-rays as low as 16,000 volts, so this is perfect. Other than changing values and flybacks, my ZVS circuit is Identical to the schematic of the Mazilli ZVS, I am not sure of the exact value of my inductors, as they were stock I had in my parts bin. Mess around! if you are building a ZVS driver, Just mess with it! They will always give you something to go by, even if it is disappointing.
Step 3: Detection and Safety
When you build something like this, It is important to protect yourself appropriately and Detect them to test if you were successful. This is harder than It might sound, as I ran into an interesting failure mode.
I am using a Russian SBM-20 based Geiger counter kit that the awesome Jeff Keyzer "MightyOhm" sells, This tube is sensitive to 1 KeV Emissions and also provides me with a serial interface for measurement and datalogging.
For protection I wear a lead radiology jacket that was donated to me by a very generous individual. If you can not afford one of these jackets or no one has donated one, A sheet of lead may be used, but with lead, you must be careful with your placement of shielding. Being soft x-rays, most will absorb in air over distance, however those that make it to you will be absorbed in your skin, so shielding is quite important.
The failure my first trials experienced were that of false reading. My Geiger counter is open framed, so it is susceptible to Ion wind discharges or corona from exposed wires at close distances. so for appropriate measurement the Geiger counter must be a at least 4 inches away, for the sake of assurance I put mine 5 feet away. The first iteration of this device did not successfully produce x-rays, as the power supply only output 10,000 volts. To low to produce enough x-rays in this tube. This led to a redo and retesting, this time with distance and higher voltage, resulting in x-rays being successfully produced. I will be gathering long exposure pictures of the tube glass fluorescing and hopefully the fluorescence of my x-ray intensifier. I will follow up with more information as this project is completed.
Step 4: Measurement Results
Here are the results of testing my X-ray generator intensity with an SBM20 Geiger Muller Detector at three feet away in 2 and 5 second bursts:
CPM: counts per minute
uSv/hr: microsieverts per hour
CPS: counts per second
CPM: 23 uSv/hr: 0.14
Two second generator burst at three feet away:
CPM: 2300 uSv/hr: 12.72 (counter switches to fast measurement mode)
Five second generator burst at three feet away:
CPS: 84 CPM: 3996 uSv/hr: 22.77 (counter is switched in fast mode)
Step 5: WIP
This project is a Work in progress, and is in the process of having data gathered. I will be shooting video and long exposure pictures of the device operating, to see if I can catch my x-ray intensifier cassette glowing and also catching the tube glass fluorescence. I have gathered some data of x-ray energies in counts per minute, and dosage rates in millisieverts. The final part of this project is a detector made from a retired high performance liquid chromatography machine detector, called a fluorescence detector. I have put a peice of intensifier film inside the Photomultiplier chamber and hope to see activity with this, This is a halted project for the time being however as I am in the process of moving, and in other projects.
For more updates more frequently refer to my blog, http://Spectrhz.wordpress.com