how-to-x-ray

7/31/2019 How-to-X-Ray

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http://www.instructables.com/id/How-to-X-Ray/

Food Living Outside Play Technology Workshop

How to X-Rayby AdamMunich on April 14, 2012

Table of Contents

How to X-Ray ................................................................................................................

Intro: How to X-Ray .........................................................................................................

Step 1: Be safe: Radiation Sickness ............................................................................................

Step 2: Be Safe: Know thy Energy! .............................................................................................

Step 3: Be Safe: Pesky Particles ...............................................................................................

Step 4: Be Safe: Use Shielding! ................................................................................................

Step 5: What is a Coolidge tube? ...............................................................................................

Step 6: How do they produce X-Radiation? .......................................................................................

Step 7: Anode Current .......................................................................................................

Step 8: Thermal Limitations ...................................................................................................

Step 9: Generating an extra-high tension .........................................................................................

Step 10: Designing a CW ....................................................................................................

Step 11: Designing *the* CW ..................................................................................................

Step 12: Oscillators! ........................................................................................................

Step 13: How the ZVS works .................................................................................................. 1

Step 14: Designing a ZVS .................................................................................................... 1

Step 15: The transformer ..................................................................................................... 1

Step 16: The cathode PSU: Switch mode power conversion ........................................................................... 1

Step 17: Making an SMPS .................................................................................................... 1

Step 18: Assemble the Radiating Head .......................................................................................... 1

Step 19: Controlling the X-ray Head ............................................................................................. 1

Step 20: What should it all look like? ............................................................................................ 1

Step 21: Metering .......................................................................................................... 1

Step 22: Nothing to see here... ................................................................................................ 1

Step 23: Radiography: X-Ray Cassettes ......................................................................................... 1

Step 24: Radiography: Recording .............................................................................................. 1

Step 25: Radiography: Setting up a still life ....................................................................................... 1

Step 26: Radiography: Kilovolts-Peak ........................................................................................... 1

Step 27: That's about it! ...................................................................................................... 2

Related Instructables ........................................................................................................ 2

Comments ................................................................................................................ 2
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Author:AdamMunich author's website

Professional hard drive formatter.

Intro: How to X-RaySo you wanna learn how to x-ray? Well then do I have some information for you!

Preface:

Why did I write this instructable? Well, to have a shot at winning that objet 3D printer!

And why would I want that?

To set up a hackerspace of course! There aren't any wi thin 50 miles of my town, and that leaves those who wish to build things; people like my friends and I, sh*t out oluck. This is especially a pain when I'm trying to design a better, manufacturable, portable x-ray machine and have no access to a 3D printer!

I've spent the better part of two months writing this guide, just for the chance to give some geeks (me included) the tools they deserve. If you could vote for myinstructable, that'd be just awesome :-)

Warning:

X-rays can kill. At the very least, they can give you cancer, which also kills. If you do not fully understand the dangers of ionizing radiation, and are not competent enoto handle voltages exceeding 50,000eV do not, under any circumstances replicate what I have done here.

Step 1:Be safe: Radiation SicknessRegular radiation such as microwave, infrared and visible light typically doesnt have the energy needed to break chemical bonds, so we may sit out in the sun andget bombarded with a thousand watts and feel no ill effects. Once we reach ultraviolet though, this radiation now has enough energy to break those chemical bondsincluding the ones in our bodies. This means that high energy radiation such as that emitted from an x-ray tube can damage DNA, and in high enough doses may evcause radiation sickness.

Acute radiation sickness occurs when your body has absorbed a large amount of ionizing radiation, usually on the order of several sieverts. What makes radiation lethis the effect it has on DNA. When a high energy particle, be it a photon or some other particle collides with DNA i t breaks bonds and rearranges the bases. Normally ycells can repair this damage, but if a cell fails at that task it often commits suicide before it divides. For long living cells such as muscle this isnt too much of a problemsince the other cells have time to replace the dead ones. For short-lived cells though, this apoptosis becomes a major issue as cells are dying too fast to be replaced.

Such short lived cells include the mucus-making cells that line the intestinal wall. When exposed to enough radiation, these mucus cells start to die off en masse, and are not replaced. No mucus cells means there wi ll be no mucus, and no mucus means there is no protection from stomach acid. The intestine stops absorbing foodparticles, acid burns the tissue, and eventually you die of sepsis. If somehow you survive this ordeal, you will now need a bone marrow transplant since the short-livedbone marrow cells have died off. Radiation sickness symptoms include nausea, stomach pain and a lack of energy, and a detailed chart of symptoms can be found he

And thats why we shield ourselves from ionizing radiation! Keep in mind that it takes a very large amount of radiation to cause radiation sickness, not something afiestaware plate or even a radium painted clock could ever produce. However, a Coolidge tube is certainly capable of generating very intense radiation!
http://en.wikipedia.org/wiki/Acute_radiation_syndrome#Signs_and_symptomshttp://https//twitter.com/#!/adammunichhttp://member/AdamMunich/http://member/AdamMunich/


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Image Notes1. Radiation Dermatitis

Image Notes1. Clarence Madison Dally. The first man to die via x-radiation.

Step 2:Be Safe: Know thy Energy!In order to reduce the amount of radiation you are exposed to, shielding is put in between you and the radiation source. This shielding reduces the amount of radiationan acceptable level. What exactly is an acceptable level though? In the end, thats up to you to decide, but generally the idea is to go as low as reasonably practicableIn order to help determine what is an acceptable level, I have here a chart of activities that expose a person to radiation. [image 1]

There are multiple different types of radiation and each type must be treated differently when it comes to radiological protection. Some types require more shielding thothers and since this is a guide I will now do some explaining. First with particle radiation, then with electromagnetic radiation. But before we do that lets discuss ener

Radiation can have different energy levels, energies which are measured in electron-volts (eV). One electron-volt is defined as the amount of energy gained by oneelectron as it moves through an electric field of one volt. For example, green light photons usually have an energy of about 2.3eV, while blue light has an energy of 3e

More energetic radiation is able to cause more damage when it hits something, and this is why microwaves such as those emitted from cell phones (0.00001eV) causchemical damage while gamma rays which may have an energy of 5 million eV can cause major damage.

Generally higher energy radiation is harder to shield than lower energy radiation, but when it comes to particle radiation the type tends to play more of a roll whendetermining penetration. Usually particle radiation tends to be the least penetrating...


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Step 3:Be Safe: Pesky ParticlesAlpha decay is the most common method of radioactive decay. During alpha decay, the unstable element ejects a duly ionized helium nucleus known as an alphaparticle. In fact, all the helium on earth comes from the decay of uranium and other elements underground.

Although alpha particles are very high energy, often having energies in the MeV range, they are very large. Because of that they are stopped very easily. In fact an alpparticle cannot even make it past a piece of paper, or even skin for that matter. Alpha particles usually have a hard time making it through more than 3cm of air, sotherefore no special shielding is necessary for alpha radiation. Just dont eat an alpha emitter and you will be fine.

The next type of radioactive decay is beta decay, a process in which a neutron is converted into a proton and in exchange an electron and a neutrino is ejected. Theneutrinos are of no concern since they are small, light and neutral, and thus pass through any matter they encounter and fly off into space like a ghost. The speedyelectron known as a beta particle has a negative charge though, so it can interact with matter and thus pose a hazard. Fortunately beta particles are not very penetratiall that is needed to shield them is a piece of aluminum.

The last type of particle radiation is known as neutron radiation; something that is created when atoms are either fused together or fissioned apart. Unlike all other formof radiation, neutrons can actually turn things radioactive! This is because when a neutron smacks an atom it may stick to it, turning that atom into another stable isotoor possibly a radionuclide. Unless you are either playing with Farnsworth Fusors or uranium reactors neutron radiation is not much of a concern, but nonetheless it is bshielded with light materials of all things, materials such as water and aluminum. Large amounts of water make an excellent neutron moderator, but because of this thehuman body does too. Therefore neutron radiation is especially dangerous to living things so do everything in your power to avoid it.

While you're not going to encounter any particle radiation when playing with x-rays, it's always best to be informed!

Image Notes1. Mspaint skills!

Step 4:Be Safe: Use Shielding!Now that we have particle radiation out of the way its time for electromagnetic radiation: highly energetic photons. There are two types of electromagnetic radiation yoshould concern yourself about; gamma and x-rays.

First lets start with gamma rays. In certain radionuclides the atoms nucleus is left in an excited state after beta or alpha decay. This energy is then released via a veryhigh energy photon. By high energy I mean several MeV, and due to that gamma rays are very penetrative. It takes quite a lot of material to stop them, so lead is oftenthe material of choice for gamma shielding. If for some reason you have a very active gamma source use plenty of lead to shield it. Something like 5cm or more of thagrey metal should be sufficient.

X-Rays

The other type of electromagnetic radiation I have to discuss is x-rays. X-Rays are produced when electrons dump a large amount of energy into a single photon, thuscreating a very high energy light particle. X-Rays are a lot like regular light: they travel in straight lines, can be reflected somewhat, and scatter in the air much like agreen laser beam. When experimenting with x-rays, always make sure your lab is of light construction. While cinderblock walls are great for stopping x-rays fromescaping your lab, they are also great for reflecting them back at you! Its better to have them escape rather than to have them bounce around.

When possible, be sure to either point your x-ray beams down to the earth or up in the air: anywhere where it is unlikely to be intercepted by an animal or human. NEVpower up an x-ray tube in a shared residence or an apartment without full knowledge that the radiation will be contained, and NEVER intentionally expose yourself to xradiation.

It is important to shield yourself from x-rays to prevent overexposure! The amount of shielding required is entirely dependent on the energy and quantity of x-raybeing stopped. Lead is the ideal shield for x-rays because it is cheap, easily workable and has a high nuclear charge; something that lets it absorb electromagneticradiation very well. For convenience I have prepared this chart of energy vs. attenuation vs. amount of lead needed using the standards set by the International AtomicEnergy Agency. [Image 1]


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Image Notes1. ...Why does instructables always mess up my images?

Step 5:What is a Coolidge tube?Essentially, a Coolidge tube is a thermionic diode optimized for both high voltages and high powers. Like a thermionic diode, all elements are contained in a glassenvelope which has been evacuated to the hardest vacuum reasonable.

A Coolidge tubes method of operation deviates not too far from that of a diode. The heater is given a bit of current to warm it to incandescence, where the now hottungsten cathode boils off a cloud of electrons while simultaneously focusing them into a beam. These electrons are then attracted to the positively biased anode andmove towards it at a very high speed. Upon arrival at the anode, the high energy electrons lose energy through collisions with the metal atoms. Most of these electronswill do little more than heat the anode, but about 2% will generate x-rays in a process called bremsstrahlung.

Image Notes1. This is a coolidge tube that I drew up in paint

Image Notes1. Some of my coolidge tubes. Send me a message if you want one.

Step 6:How do they produce X-Radiation?1. Bremsstrahlung

Literally translating to braking radiation, bremsstrahlung is the process where a high speed electron brakes and sling-shots around an atom's nucleus, dumping itskinetic energy on one photon. An imparting electron might have an energy in excess of 60keV so some very energetic photons are be made; photons which fling off inspace and become the x-rays we all know and love.

What determines the energy of the x-rays produced is the amount of voltage present on the anode. Its quite simple actually; more voltage means more electronattraction, and more attraction results in a faster electron beam. Faster electrons are able to make higher energy photons, and thus harder, higher energy x-rays woube generated.

Bremsstrahlung is a continuous spectrum of radiation akin to a white light source. Since most electrons graze a few atoms before they have the chance to sling-shotthey often lose some energy before they make any x-radiation. A whole range of x-ray energies is thus produced.

The maximum energy that an x-ray can have is limited to the energy of electron producing it, itself directly proportional to the voltage applied on the tubes anode. Oftethis energy is measured as kilovolts peak, or kVp. In reality the majority of the x-rays produced are low energy, soft x-rays, but these are greatly attenuated by thetubes glass wall.

2. Characteristic Production

Characteristic or k-line production is the second mode in which an electron might produce an x-ray. In this method, electrons knock others out of an atoms lowermostshell and leave a hole which must be f illed. This unstable arrangement is then promptly made stable by electrons from higher shells who jump down to fill the hole,emitting an x-ray photon during the journey.

Tungsten k-shell electrons have a binding energy of 69.5keV, so to kick these out your impacting electrons must have energies greater than 69.5keV. Typically one woneed to give the anode a bit more than 72kV to accomplish this, hence the standard 75kV x-ray tube.

After a k-shell electron gets the boot, its hole will immediately be filled by an electron from tungsten's l-shell; binding energy 10.2 keV. The difference between these tw

energy states; 69.5 keV and 10.2 keV gives us the characteristic tungsten x-ray energy of 59.3 keV. A molybdenum anode would produce two peaks, one at 19.7keV the other at 17.6keV.

Interestingly, this process can be used to identify elements based on their k-lines. By bombarding a sample with electrons and measuring the output spectra, an x-rayflorescence analyzer can determine what elements a compound contains.


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Image Notes1. A typical emission spectrum

Image Notes1. Bremsstrahlung!

Image Notes1. Characteristic Production!


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Step 7:Anode CurrentWhile anode voltage controls the hardness of the x-rays, the voltage applied to the tubes heater gives independent control of the total x-ray flux. A hotter cathodeboils off more electrons, reducing the impedance and allowing for a larger current to flow through the tub. One must be careful though, as too much power will damagethe tubes anode via excessive heating. Ideally, a medical x-ray generator would provide a short, high intensity burst of radiation to reduce the shutter speed andoverall dose absorbed by the patient.

Conveniently, these tubes usually come with some graphs to help one set parameters for the design of a machine; [image 1] displays the relation between heater voltaand anode current for the tube which I 've chosen. From what the curve tells, one must apply 2.6V to the heater in order to allow a decent 3mA to flow through the tubeanode. While 3mA might not sound like a lot of current, at 75,000V that is a respectable 225 watts of power! Assuming a typical 3% efficiency, this would equate to 6.7of x-ray energy out.

When one thinks about how a 100W light-bulb emits on average 4 watts of visible light, it becomes quite clear that the tube will emit quite a hefty amount of radiation;certainly enough to expose a film.

Step 8:Thermal LimitationsA critical value which must be known is the anodes heat storage capacity. The tungsten/copper anode has a limited thermal conductance, thereby limiting its ability todissipate the great heat generated by the focused electron beam. To cope with this Coolidge tubes often are run at a duty cycle, limited by both the operating power, athe anodes heat storage capacity. In a typical Coolidge tube this heat capacity is usually 7kJ.

Fortunately, manufacturers of both x-ray machines and x-ray tubes are required by federal law [CFR Title 21] to provide anode heating and cooling curves for theirdevices [image 1]. It's evident that operating this tube at a power of 225W would limit the maximum exposure time to a bit less than 1 minute, with a 5 minute cool-dowperiod. Of course x-ray exposures are never actually 1 minute long; usually they are only a few seconds at most.

Provided the tube is not abused, 225W would not be an unreasonable power to operate it at .


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Step 9:Generating an extra-high tensionThere are many methods of generating high voltages, including but not limited to Tesla coils, induction coils, Marx generators, Van-De-Graff generators and Cockroft-Walton cascades. Even some unorthodox methods such as piezoelectric and pyroelectric crystals exist.

While all of these methods have their advantages and pitfalls the Cockroft-Walton voltage multiplier would be the circuit of choice for this project. Properly designedcascades are capable of transforming large powers with comparatively lit tle loss, and their lightweight and small stature make them well suited for a small x-ray genera

Refer to the first schematic. By feeding an alternating current into this circuit, one can sacrifice cycles and current in return for a doubled, tripled or even quadrupled Dvoltage. All and all the circuit's mode of operation is rather simple, as it is nothing more than a cascade of Greinacher voltage doublers [second image]

On the negative alternation, the bottommost plate of C1 is charged to -10kV via D1. Afterward, the positive alternation puts C1 in series with another 10kV creating a tpotential difference of 20kV, which is shared wi th C2 via D2. This 20kV can then be discharged, or another cascade may be added to create 30kV, or another to make

kilovolts. In reality though, it takes several more cycles for the stack to reach its full potential due to parasitic resistances limiting what would otherwise be very highcurrents.

Step 10:Designing a CWThe maximum voltage which may exist between ground and stage n can be predicted using the above formula.

There is nothing overtly complex about this math; it's simply the peak DC input value multiplied by the number of stages in the multiplier stack. Of course, this is only ththeoretical output voltage. Large high voltage capacitors are expensive and bulky, so in most cases we are stuck using small capacitors and their high XC .

Now take a gander at equation #2.

The large impact of n in the latter half of the equation tells that using as few stages as possible in a multiplier will help minimize voltage drop. Fewer stages would meafewer series-strung capacitors, and thus a lower XC . Likewise, I ( f * C ) tells us that both higher frequencies and larger capacitances will reduce the voltage drop unload. In both scenarios XC would be reduced. A practical multiplier would thus contain no more than 5 stages, operate at a very high frequency and have capacitorswhose values are not less than 500pF.

This problem is compounded by the fact that many capacitors are placed in series in a mult iplier. The high impedance nature of this circuit allows any sort of load to pudown the voltage substantially. This pulldown can be so profound that time was spent developing a formula to estimate the voltage drop under various conditions.


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Step 11:Designing *the* CWA typical multiplier for an x-ray machine will consist of 4 stages, themselves consisting of a pair of series-connected 1.5nF, 15kV capacitors and another pair of 2 seriestrung 15kV ultra-fast diodes. This gives the equivalent of 30kV 750pf capacitors and 30kV diodes, respectively.

The operating frequency should be set to 70kHz to keep capacitive losses in the transformers windings to a minimum, yet that still should be high enough to push 3mthrough without too much voltage drop.

Please refer to image #2.

This 2.6kV drop is certainly reasonable and may be compensated for by increasing the input voltage by an additional 650 volts.However there is one minor problem; this formula is for the most part, useless. While the theoretical voltage drop should be 2.6kV, it will most likely be on the order of 12kV. Although this is significantly higher than predicted is not impossible to compensate for by upping the frequency and input voltage a bit.

Image Notes1. The CW which I made

Image Notes1. Typical CW stats

Step 12:Oscillators!A CW multiplier still requires a moderately high voltage, high frequency input. Obviously this cannot be obtained from a stack of 5,000 AA cells, so it must be generatevia some oscillatory witchcraft. The most logical spell would of course be a forward mode flyback converter, preferably one which switches on the zero voltage or zerocurrent crossing point to minimize losses.

In order to obtain 225W at 12kV we need 54mA, and assuming a 100% efficiency wed likewise need to draw 6.25A from a 36V source. Of course 100% efficiency isunobtainable, but 10A at 36V is still not unreasonable for a hobbyist to supply.

A choice oscillator for this task is the current-fed ZVS Oscillator; an LC resonant zero-voltage switching circuit. Although a Hartley or a Colpitts oscillator could be usedboth are not switched under no-load conditions, and would thus burn significant amount of power when the MOSFET travels through its linear region.


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Image Notes1. An oscillator

Step 13:How the ZVS worksPlease refer to that schematic [image 1].

When power is applied to the circuit, current begins to flow through L1 and into the MOSFETs drains via the center tapped load coil. Simultaneously, this voltageappears on both gates and begins to turn the MOSFETs on. Since no two FETs are alike, one turns on faster than the other and drags down the voltage on the opposMOSFETs gate. One FET is now latched on while the other is off. The tank capacitor prevents the circuit from staying in this state as the LC resonance causes asinusoidal reactance in the circuit; reactance which will flip the MOSFETs states and feed more current into the tank. This oscillation keeps going until power isremoved, or some instability such as a saturated load inductor latches one MOSFET on and explodes the circuit.

While the circuit would work in theory, such an oscillator proves to be very unreliable without some modifications. Instead of connecting the gates directly to the LC tanitd be wiser to instead leave them normally pulled up via a pair of resistors, where the LC tank would alternately ground the gates via ultra-fast feedback diodes. Thismethod ensures that no stray currents lock up the gates and kill the circuit. [image 2]

Of course MOSFET gates will not tolerate a VGS in excess of 30V, so it is a wise idea to use 18V zener diodes to protect the gate from such excess voltages. 10Kdischarge resistors ensure that no stray charges are left on the gate while it is being pulled down by a feedback diode.

If that confused the hell outt'a ya, this simulation might help!
http://www.falstad.com/circuit/#%24+1+1.0000000000000001E-7+3.046768661252054+40+5.0+43%0Ar+400+384+400+464+0+10000.0%0Az+352+464+352+384+1+0.805904783+20.0%0Ar+720+112+640+112+0+470.0%0Ar+448+112+368+112+0+470.0%0Az+736+464+736+384+1+0.805904783+20.0%0Ar+688+384+688+464+0+10000.0%0Ac+480+272+608+272+0+6.800000000000001E-7+-41.76984622682506%0Aw+608+272+608+320+0%0Aw+480+272+480+320+0%0Ad+576+384+576+320+1+0.805904783%0Ag+544+480+544+528+0%0AR+544+112+544+48+0+0+40.0+20.0+0.0+0.0+0.5%0Aw+608+320+608+352+0%0Aw+656+368+688+368+0%0Al+608+192+608+112+0+4.7E-5+-1.8618457035242666%0Al+480+192+480+112+0+4.7E-5+1.059247391922327%0Af+656+368+608+368+0+6.0%0Af+432+368+480+368+0+6.0%0Aw+480+352+480+320+0%0Aw+432+368+400+368+0%0Aw+400+368+352+368+0%0Aw+688+368+736+368+0%0Ad+512+384+512+320+1+0.805904783%0Aw+512+320+480+320+0%0Aw+576+320+608+320+0%0Aw+576+384+512+432+0%0Aw+512+384+576+432+0%0Aw+512+432+448+432+0%0Aw+448+432+432+416+0%0Aw+432+416+432+368+0%0Aw+576+432+640+432+0%0Aw+640+432+656+416+0%0Aw+656+416+656+368+0%0Aw+480+384+480+464+0%0Aw+608+384+608+464+0%0Aw+480+464+480+480+0%0Aw+480+480+544+480+0%0Aw+544+480+608+480+0%0Aw+608+480+608+464+0%0Aw+688+480+608+480+0%0Aw+736+480+688+480+0%0Aw+400+480+480+480+0%0Aw+352+480+400+480+0%0Aw+736+192+736+368+0%0Aw+352+192+352+368+0%0Aw+736+464+736+480+0%0Aw+688+464+688+480+0%0Aw+688+368+688+384+0%0Aw+736+368+736+384+0%0Aw+352+368+352+384+0%0Aw+400+368+400+384+0%0Aw+400+464+400+480+0%0Aw+352+464+352+480+0%0Aw+512+112+544+112+0%0Aw+544+112+576+112+0%0Aw+608+112+576+112+0%0Aw+480+112+512+112+0%0Aw+608+256+608+272+0%0Aw+480+224+480+272+0%0Al+496+208+592+208+0+1.9999999999999998E-5+6.864568774296518%0Aw+368+112+352+112+0%0Aw+352+192+352+112+0%0Aw+448+112+480+112+0%0Aw+480+192+480+208+0%0Aw+480+208+496+208+0%0Aw+592+208+608+208+0%0Aw+608+208+608+192+0%0Aw+608+208+608+256+0%0Aw+640+112+608+112+0%0Aw+720+112+736+112+0%0Aw+736+112+736+192+0%0Aw+480+208+480+224+0%0Ao+9+4+0+35+69.99202319305638+0.3499601159652819+0+-1%0Ao+22+4+0+35+65.46781215792284+0.3273390607896142+0+-1%0Ao+59+4+0+35+80.0+12.8+1+-1%0A


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Step 14:Designing a ZVSSince it's nothing more than LC oscillator, a ZVSs operating frequency may be derived with the parallel resonance formula [image 1]

Parallel resonant LC oscillators often have a poor tank power factor, with this one being no exception. When drawing 8 amps the circulating tank current may exceed50A! This can become a problem if the DC resistance of the load coil is high. To combat this one may wish to use a larger capacitor than inductor, since a metalizedpolyester capacitors parasitic resistance tends to be smaller than a large coils.

[look at image 2]

Since we designed the CW to run on 70kHz we'd need that same frequency out of this ZVS. To achieve that with 680nF of tank capacitance, wed need roughly 7.5?Htank inductance or about 5 turns of wire on an average ferrite core. Since 5 turns of copper wire has for the most part an insignificant series resistance I^2 R losses in coil will be minimized.Trouble may arise if the coil voltage raises high enough to saturate the transformer's core, but an air gap should solve any issues.

Step 15:The transformerSince commercially produced HV transformers are hard to come by in small quantities, the transformer for your x-ray machine must be either salvaged or handmade.Usually the best thing to do is to find an AC flyback transformer and swap its core for something heftier.

Special attention must paid to prevent saturation that could otherwise occur at 15 volts per turn; pick a core with a low permeability, a large cross sectional area, a smamagnetic path and then set a 0.5mm air gap.


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Image Notes1. A DC flyback core stuck into an AC flyback secondary. It's madness!

Step 16:The cathode PSU: Switch mode power conversionAn X-Ray tube requires a low voltage, high current power supply to energize its heater; something which must be derived from the 14V bus. A linear regulator would baway unacceptable amounts of power so a switch mode regulator must be used instead. If grounded the cathode does not require an isolated power supply, so a simpbuck topology may be used to provide the regulated voltage it requires.

Buck converters are the simplest of the switch-mode topologies. Essentially the circuit measures the voltage across a capacitor, and attempts to maintain a set voltagevarying the current supplied to that capacitor. Often this is done by varying the duty cycle on a rapidly switching MOSFET. While that might sound good in theory, inpractice the very high currents experienced by the MOSFET would increase losses to intolerable levels. In the real world, an inductor is placed in series with the MOSto more or less average this current flow.

This solution creates another problem though. Quickly interrupting an inductors current flow would create damaging high voltage spikes which could destroy theMOSFET. Typically, this is solved by putting a diode in antiseries with the inductor, but that would create a very lossy circuit. Instead, the diode is placed in antiseries the load.

Peek at [image 1]

When the switch is closed, current flows through the load and filter capacitor via an inductor. When the specified voltage is reached on the capacitor, the switch isopened. Both the inductor and capacitor then deliver power to the load via a schottky flyback diode until the voltage falls enough that the control circuit once more turnon the MOSFET.

This happens thousands of times per second.


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Step 17:Making an SMPSWhile it might be a bit cheaper to build a buck converter out of discrete components, using a "Simple Switcher" f rom National Semiconductor (well, TI now) would be thwisest, most reliable option. Perfect for the job is the LMZ12003 buck converter IC which has an inbuilt inductor. Averaging 94% efficiency in a surface mount packagethis IC in my opinion is a feat of semiconductor engineering like no other!

Fortunately there is not much hair pulling to be done using this IC, apart from setting the feedback reference via a voltage divider connected to the output. This feedbapin feeds into an inbuilt comparator which the onboard oscillator uses to set the MOSFETs duty cycle.

Be sure to put a big TVS diode across the IC's output! If this device fails shorted and there is nothing to clamp down the voltage, you'll burn out the cathode in yourcoolidge tube!

Image Notes1. Adjustable!

Step 18:Assemble the Radiating HeadAtmospheric air has a dielectric strength of 1.1 million volts per meter despite what Wikipedia argues. This translates to 11kV per centimeter, or 6kV with pointedelectrodes. Since reliably insulating 75kV using air would require a distance larger than 10cm,making an x-ray device compact is near impossible.

That is of course, if one does not use insulating oil!

Most oils have a dielectric strength 4 times that of air, and eliminate the corona losses which would otherwise occur in an open air design. This reason, coupled with

increased thermal conductivity is the reason why nearly all x-ray machines insulate all of their high voltage components with oil, and why both mine and yours shouldfollow suit.

A junction box does a fine job of housing the EHT components. [Image 1] displays the junction box which houses my machine's Coolidge tube, its lead shield, the voltamultiplier and a 1.8 billion ohm resistor to measure the anode voltage. A 90kV this resistor will leak the 50uA needed to fully deflect a galvanometer.

The thickness of the boxs wall will attenuate the x-rays somewhat so there likely wont be any low energy rays escaping. Depending on what you want to do this may may not be a problem, but, x-rays with energies higher than 30keV should still be able to penetrate that thick plastic.

Image Notes1. Bread


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Step 19:Controlling the X-ray HeadNow that the x-ray producing network is designed and assembled, we'll need another network to control everything. Now this can be as simple as a 555 timer and a ferelays, but that wouldn't be very fun now would it?

Typically, an x-ray machine follows the following operating procedure:

1. The technician chooses an exposure time and kVp.2. The tubes heater warms up for a short period.3. High voltage is turned on and x-ray photo is taken.

Its a process that must be replicated in my machine. The safest, most logical method would be to base the circuit around a micro-controller. Not only would amicrocontroller be reliable, but it would have the added benefit of allowing for easy modification later on.

Which is why I used an arduino.

Step 20:What should it all look like?A project doesn't need to look nice to function, but making it look nice is one of the best parts of building something. To make something look nice though, one needs first figure out what that something should look like.

My 'something' has gone through several alliterations [images 1, 2], but in the end it was best to just put it in a wooden craft box. If I had access to a 3D printer I mighthave gone a different route, but alas, all I had at my disposal was a ratty old CNC machine.

It did do a good job routing the pinewood though, and in doing so it allowed my instructable to be eligible for this contest :-)

Image Notes1. The first version was a big lead box!

Image Notes1. The second one was still a bit awkward...


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Step 21:MeteringLooking nice is pretty useless in itself though; the parts that make a project look nice should actually do something. These parts, in my case were the display, controlknobs and kilovolt/milliampere meters.

You might remember the 1.8 billion ohm resistor that I placed inside the oil filled box. That resistor will allow 50uA through when 90kV is placed across it, so by placing50uA FSD meter in series with it we create a 90,000V meter. All that's left to do is make a scale!

Measuring the anode current takes a bit more math. No calculus though, just ohm's law. Before we calculate anything though, let's set some variables. The meter is100uA full scale deflection, and we'd like to make it 3mA. Looks like we'll need a resistor!

Take a look at [image 2].

This is the scenario we must create. In order to do so though, we're going to have to measure the impedance of the galvanometer. An ohmmeter does a good job of thand in this case the coil's impedance was 5 kiliohms.

See [image 3] for the maths!


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Step 22:Nothing to see here...Now I'm not going to delve too deep into the actual design of my controller box. Why? Well, it's all pretty boring and doesn't teach anyone anything new! I will though, ga whole bunch of annotated pictures that describe the insides for those who are at least a bit interested.

[They are above]

Image Notes1. IN-12 Nixies2. Kilovoltmeter3. Milliammeter4. kVp knob5. Expose!6. On, Off

7. Timesetting/control knobs

Image Notes1. Two lithium ion batteries go here2. Relay. Yeah, I probably should have used a mosfet.3. ATMEGA368, with arduino bootloader4. Voltage regulator 15. Speaker6. Octal base, used as a cable connector.7. Filter caps8. Small relay9. Another 5V regulator10. Fuses. YOU MUST USE FUSES. ALWAYS.11. Another voltage regulator

Image Notes1. These neon lamps will provide an alternate path if the meter goes open circuit.2. Nixies!3. Really old ohmite pots. Made in USA!4. 170V inverter5. Rectifier bridge for nixies.6. BCD-Decimal line decoder.7. Capacitively coupled transistors to multiplex the anodes.8. Fuses!


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Step 23:Radiography: X-Ray CassettesX-Rays are invisible, much like infrared l ight. Unlike infrared light though, they are very energetic and are more than capable of exciting atoms, possibly a whole bunchthem. What do you get when you have excited atoms?

Photons! Lower energy photons, ones which we can see. We can use this property, 'X-Ray Fluorescence' to convert an x-ray beam into visible light, allowing us towitness the information contained within it. Often times, this is done with something called an 'intensifying screen'; a plastic sheet impregnated with an x-ray responsivphosphor.

Intensifying screens are contained in intensifying cassettes; little l ight tight folders which house x-ray fi lm. [Image 1] ought to give you a good idea of what these thingslook like.

Types of Cassettes

Like many things in this world intensifying cassettes come in many flavors. Blue, Green, Rapid, Ultra Rapid, Normal...

'Ultra Rapid' screens will give you the brightest images, and thus shortest exposure times. This is not without its downfalls though. In order to appear bright, the crystathese screens must be very large; large enough that the resulting image is a bit blurry.

'Regular' screens will likewise produce a sharper image, albeit a dimmer one. More x-rays and longer exposure times would then be needed, but this is the price we p

'Fine' cassettes will produce a very sharp image. Unfortunately it 's also a very dim image...

Image Notes1. X-ray Cassettes

Image Notes1. Usually there are two screens inside one of these.

Step 24:Radiography: RecordingThere are a number of ways one can record an x-ray image.

+ The most traditional method would be to place a piece of paper film inside a cassette and develop it later. Although plastic-based film is certainly on death row, papefilm is still readily made and bought by millions of people, and it's not going to go away any t ime soon. Usually one can pick up 100 sheets for about $90 on ebay ;actually not too bad when you consider the price of printing high quality photos. [image 1]

+ The second, more modern method of imaging x-rays would be to use a flat panel detector. These however, cost $60,000 each. [image2]

+ A third method would be to tape the intensifying screen to a sheet of lead glass, then placing a digital camera behind it. Albiet a bit crude, a DSLR camera set to 10second timer will do a fine job of imaging the screen. Lead glass is a must though, otherwise there will be a firestorm of noise in your image! [image 3]

If you have the money to spare, adding an image intensifying tube to your camera wil l greatly reduce the exposure time. Do not however buy a gen 1 or gen 2 tube;they're terrible, Go for generation 3 or nothing! [image 4]
http://www.ebay.com/sch/i.html?_sacat=0&_nkw=enlarging+paper&_nkwusc=elarging+paper&_rdc=1


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Image Notes

1. Kodak went out of business, thus giving these guys a monopoly!

Image Notes1. This costs about $24,000

Image Notes1. Intensifying screens peel right out of the cassettes. Just tape it to a piece ofleaded glass and it's good to go!

Image Notes1. Image intensifier. Also rather expensive.2. Gen 3 photomultipliers have shiny black photocathodes. Gallium arsenideactually.

Step 25:Radiography: Setting up a still lifeX-Rays cannot be bent, reflected or focused like normal light, and there's no way to make a camera obscura, much less an actual camera to capture an x-ray image.Resultantly, the only method of taking an x-ray image is via a shadow, or silhouette process.

It's not all that hard to set up for an x-ray image.

The first step, of course is to wait until it is dark outside. Now unless you happen to have a lead-lined room, I do not under any circumstances condone indoorradopgraphy. There are simply too many surfaces for the x-rays to reflect off of, especially if your house is of heavy construction.

The best place to take a radiograph is in your backyard with the beam pointed away from anything animate. A few acres of woodland for example, is a good target. Yoneighbors house on the other hand, is not. That is, unless it is more than 80 yards away, in which case inverse square law reduces the radiation field to nil.

DO NOT EXPERIMENT WITH X-RAYS UNLESS YOU LIVE IN A SUBURBAN OR RURAL COMMUNITY. DO NOT, power up an x-ray tube in an apartment.

Now that we have some wanrings out of the way, let's get back to sti ll lifes. It's not a terribly complex science; all you need to do is set up your x-ray source, your imagdevice, and your object which is to be radiographed. The closer you place your object to the source the greater the magnification will be. Likewise, placing it directly infront of the film will produce a near life-size representation.


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Image Notes1. Still my favorite radiograph!

Step 26:Radiography: Kilovolts-PeakHopefully you designed your x-ray machine to have an adjustable kilovolts-Peak. By doing so, you're able to adjust the image contrast. Higher voltages would meanhigher x-ray eneries, and thus deeper penetration. The best way to describe this would be to show a few images...

[Image 1] is a radiograph of a steel gauge, set to a proper kVp for the job. Notice that all of the gauges are visible, albiet with the lighter ones a bit hard to see.

[Image 2] shows the same gauge, but at a higher kVp. The lighter gauges are now all but invisible...

[Image 3] shows the same gauge yet again, but this time at a lower kVp. Now everything is too dark.

[Image 4] is a flower imaged at about 28kVp. If we weren't able to adjust the kVp so low then the flower would be completely invisible! This is the benefit of building yoown x-ray machine instead of buying one; you can adjust the kVp to whatever you want, not just from the usual 50 to 75kVp a dentistry machine will provide.

[Radiographs courtesy of Leslie Wright ]

Image Notes1. There are fewer x-rays making i t through the thicker gauges; thus they appeardarker.
http://www.fineartradiography.com/index.html


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Step 27:That's about it!That's all there is to radiography!

All and all, it's an art and not a science. Like any art it takes practice to get good results, so don't be suprised if your f irst few x-rays look like crap. This is a dangerous though, so please, be careful.

Also, please vote for me :-)

Some more information about radiography:

c4r0's siteteralabHenning Umland's siteJochen's SiteLeslie's SiteUzzor2k's

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Comments

10 comments Add Comment

dreadengineer says: Jun 7, 2012. 10:48 AM REPSteps 2-4 were a great explanation of radiation. It's good to see that there are at least a few well-informed people on the Internet!

PuffinEM says: Jun 7, 2012. 9:51 AM REPI would vote twice if I could. Trul a GREAT instructable.

t.rohner says: Jun 7, 2012. 8:14 AM REPFantastic instructable. You have my vote and 5*.

Very good explanation of the electronic design.

When i was around 11, i met a guy who teached me the basics in electronics.(That was around the time the internet (not http://www.) was invented.

He had salvaged Roentgen devices, that had been used by shoe dealers to check, if the shoes fit.I don't exactly know, when they stopped using them. It was before my time... I guess it was in the early sixties.

He also used them for photographs in a big lead-clad wooden box.Mosfets haven't been en vouge back then.But he was very fit in all things electron valves. He learned electronics, when the first transitors became available...

One of the best instructables i've seen.

alinashea says: Jun 7, 2012. 6:24 AM REPAs much as I love the look of these photographs, I know that I will never be the one to take them. Awesome instructable and an amazing amount ofinformation about x-rays. Thank you so much!

mirthmgr says: Jun 6, 2012. 1:40 AM REPThis is the most fun I've ever had reading an Instructable that I had no intention of attempting myself. I greatly appreciate the detail and background

rovided. I, like mathsterk, would also love to see more ima es (the flower reall is stunnin ). If ou take more, I think we would all a reciate a aller !

mathsterk says: Jun 5, 2012. 2:37 PM REPWow, the image of the flower was cool. Would have been nice if you took some other pictures and uploaded them :)

radiograf says: Jun 5, 2012. 9:32 AM REPAs someone who takes x-rays for a living, can I just stress that the use of ionizing radiation is highly regulated in most countries. Also that x-rays areproduced in all directions, not just a beam from the front, so you definatly need some sort of shielding .A lead equvilence of 2mm is required here in the UKI must say that you have definatly produced a well informed instructable, and appear to have a greater knowledge of x-ray production than most of thestudents I have to deal with on department.Well researched and well done.

radiograf says: Jun 5, 2012. 9:54 AM REPcheck out: http://www.uhb.nhs.uk/radiation-protection-services.htm for more info on radiation protection, and the law here in the uk. Also www,sor.uk.orthe website of the Societ of Radio ra hers

nanosec12 says: Jun 5, 2012. 8:22 AM REPThis is one of the most informative and well written instructables I have seen !!!

5 stars, + a vote !!!

Nano_Burger says: Jun 5, 2012. 7:36 AM REPActually, you can "kind of" focus soft X-rays with a photon sieve. It is focusing with diffraction like a pinhole camera not refraction like a glass camera lens.Not sure focusing would do you much good with your set up though.

Always wanted to try this and electon microscopy. I'm waiting until my reproductive years are over though 8-)

Got my vote.
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