Needing more than a spark test?

graham-xrf

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I have some chunks of nice steel, 31mm thick and 120mm x 60mm (about 1.2" thick and 4.7" x 2.3").
The 31mm apart faces are parallel to within a tenth thou, so they are sometimes handy as a sort of fat parallel, but the perimeters are not as in a rectangular block. They have the profile of whatever hydraulic pump kit they were originally destined for.

They don't rust - so not just some nearly tool steel.
They are magnetic, so mostly iron in there.

It seems there is not much between the "spark test" on a grinder, and some expensive kind of analysis.
I can't afford one of those FLIR things which are only cost-effective if they are identifying exotic stuff all all day long.
Trying for density once let me identify a nice chunk of titanium, but I did have some other clues.

Is there some lower cost way of figuring out what is in the alloy?
 

RJSakowski

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A good question. As far as I know, no there isn't. The problem with identifying steels is that the alloying elements are usually not found in significant percentages and that many are common to an multitude of alloys so a simple qualitative test isn't sufficient.

My very first chemistry course lab in collage was qualitative analysis. Back then, this was usually done by dissolving a sample in acid and adding various reagents to create a signature reaction. My recollection is that the transition elements of which the major steel alloying metals are members were particularly difficult to identify.

One test that might be used is a flame test. It consisted of dipping a small platinum or nichrome loop into a dissolved sample and the placing the loop in a flame from a Bunsen burner. Different elements will color the flame differently. Unfortunately, it doesn't work with all elements.

Once an element was identified, then you have to analyze it for the particular amount in the alloy. My first professional job was as an analytical chemist designing analytical procedures for various materials. Many of the elements will interfere with each other, making an analysis difficult. A method known as polarography was used to perform some of these analyses. Another tool that we used was emission spectroscopy. that provided a relatively quick means of identifying materials. It consisted of placing a dissolved sample in a carbon cup and firing high voltage through the sample. The resultant light was captured and its spectrum recorded on a photographic plate. Unfortunately, the cost of an emission spectrograph is beyond the reach of any except large laboratories.

All this testing provided job security for chemists in the past. Which is why x ray fluorescence is the tool of choice today.
 

homebrewed

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Here's a description of a "DIY" XRF setup: DIY XRF. It uses americium capsules from smoke detectors as the X-ray source. But you'd still need to get your hands on a PMT and scintillator crystal, and be willing to spend a lot of time messing with it (getting it to the point of making quantitative measurements would be a heavy lift for a DIYer). Make sure you have some lead-lined shorts :D.
 

graham-xrf

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I have only 0.9 mirocuries of Americuim 421 here on my desk, and possibly 2 microcuries down in the garage.
I have 2 photomultiplier tubes with the green flourescent back screens laying about in the cellar. Three if you count the cheap Russian night-sight. Honestly - I think there may be easier ways of making a pulse of X-Ray.

You are right about it being a DIY heavy lift attempt. Pity one needs X-Rays.

I am OK to dissolve a bit of this stuff, and try some flame test. The only platinum wire I have is a bit thin, it being from platinum-rhodium thermocouple, but it may do. I have sulphuric (OK - sulfuric) acid. It kind of pre-supposes all the alloy metals in there can end up as some sort of sulfate, no matter the valency.

Maybe if I can at least discover some of the alloy metals in there, then try a thin piece for melting, and see what happens if I heat-treat a bit to see if it self-hardens or something. It may narrow down the possibles. Given that it does not rust, there might be nickel, chromium, molybdenum maybe.
 

graham-xrf

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@RJSakowski : The flame test looks somewhat limited when we are after the steel alloys.
Is it realistic to conduct a chemical test for these, just assuming they are there, even if they prove not to be?

A first test for iron can yield a percentage, which then immediately reveals the remainder proportion being all the alloying elements?

Would the Curie temperature of the mix be a tell-tale as to which steel it might be?
If it corresponds to a known steel mix, the thing is revealed. I have visions of heating a lump of it, with a thermocouple stuck into a drilled hole, until a magnet lets go. Hmm.. we need the magnet material coupled in a way that the magnet does not die first!

In any case, any one of the XRF hand-held fancy kits is likely to cost a whole lot more than my entire machine, and all it's bits!
 

ericc

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I don't think that the Curie temperature will tell you that. This is more of a decalescence thing. You have to have a good eye and a precise temperature reading to do this. One could possibly do it with a muffle furnace and an accurate pyrometer.
 

RJSakowski

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@RJSakowski : The flame test looks somewhat limited when we are after the steel alloys.
Is it realistic to conduct a chemical test for these, just assuming they are there, even if they prove not to be?

A first test for iron can yield a percentage, which then immediately reveals the remainder proportion being all the alloying elements?

Would the Curie temperature of the mix be a tell-tale as to which steel it might be?
If it corresponds to a known steel mix, the thing is revealed. I have visions of heating a lump of it, with a thermocouple stuck into a drilled hole, until a magnet lets go. Hmm.. we need the magnet material coupled in a way that the magnet does not die first!

In any case, any one of the XRF hand-held fancy kits is likely to cost a whole lot more than my entire machine, and all it's bits!
Graham, Last things first, Yes, a quick check on eBay shows xrf testers in the $6K range. Well beyond reason for anyone not using one for major business.operations. I think a business opportunity could be possible for someone doing testing for hire on mail-in samples.

I'm not sure that you would be able to distinguish different steel alloys by their Curie temperature. If it were possible, a more accurate test than simply looking for the temperature of loss of ferromagnetism. The is a tool called a differential scanning calorimeter which I understand can be used for measuring the Curie point. I haven't used it myself but about twenty years ago, one of our epoxy suppliers used into determine the extent of curing in an epoxy. It looks like the eBay prices are somewhat better than xrf but it really wouldn't tell you much about the composition of the steel.

A colorimetric test could be developed for measuring the percentage of iron. Again, I'm not sure it would be precise enough to identify an alloy. When looking at the composition of steel alloys, all of the components have a range with iron usually listed as balance. That said, iron forms some highly colored complexes the intensity of which can be measured with a colorimeter or by comparison to a color chart. To do so, a sample of known weight has to be dissolved and and diluted to a known concentration. Then the sample is compared to a color chart or, for more accurate values, the absorbance of a certain wavelength of light by the sample is measured. That's the simple version. In reality, checks for possible interferences need to be done, standards of known concentration have to be made and host of other possible issues have to be dealt with.

There are other means of measuring the amount of iron and other metals in an alloy. I had developed a titration procedure for measuring manganese which could also be used to measure iron concentration. Potentially metals like cobalt and vanadium could be measured in that way as well. But these are better suited to an analytical laboratory than a machine shop.
 

hman

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No joy, folks :(

Way back when I was a chemist, I learned about an instrument called an Atomic Absorption spectrometer. It was used for quantitative analysis of dissolved metals. For any given metal, the light source was a specific "hollow cathode" arc lamp containing that metal. Then there was a gas fueled burner, which had a long line of small holes - maybe 3" or 4" - through which the light was sent. The dissolved sample was slurped/atomized into the gas stream to "color" the flame. The length of the burner was necessary for sensitivity.

Light passing through the line of flames was measured with "some kind of" photocell detector. The amount of light passing through the flames would be reduced by whatever target metal was present in the flames, because the atoms would absorb some of the light from the source. The difference in readings between no-sample and sample, times a suitable absorption factor, times the concentration of sample dissolved in the solution under test, would give the concentration of the target metal in the solution.

It was a very persnickerty and involved test method, to say the least! And not that many metals could even be tested.


As far as a DIY "eyeball" flame color test, you're more likely than not to have a small quantity of sodium in the solution. Sodium gives a bright yellow light, which can overwhelm and mask the color(s) that might be there from other metals.
 

graham-xrf

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Wow! Between @RJSakowski and @hman , I seem to have unearthed the experts who are steeped in a combination of chemistry, physics, and element analysis at atomic level. I have images of periodic table pinned up next to the Starrett Tap Sizes chart!

OK - I guess since the steel was free, I can use it on whatever it seems handy for. You are right that the costs of knowing are unjustified.

As it happens, I do have enough alpha emitter material, to get up about 8 uCuries, and I already posses some photomultipliers, but they unfortunately only the type used for night vision cameras. The rest of the stuff I don't have. HM folk, especially those deep into CAD, CAM, and CNC kit, would probably find this well within their capabilities.

For those who might want to try..
You need to raid some smoke detectors. 8 or 10 of them, old or new.

The rest of the assemblies you can vary to your taste. You might want to turn up a mounting, or adapt some metal tubing.

I see one can get various kinds of scintillation crystal, and the Cesium Iodide type is $51.50 + $14.50 postage to UK
--> CsI crystal eBay

A new Hamamatsu Photomultiplier is about $90, but then, there is the mountain to climb to build the rest of the instrument, physical mountings etc. The information for the photomultiplier electronics is all there for some little printed circuit boards You can use other photomultipliers.

--> Hamamatsu Photomultiplier

--> PmTAdapter This appears to be a little opto-isolated highvoltage, low current supply for the photomultiplier.

and the little PIC microcontroller board --> ThereminoMCA

The software appears to be free.
The data for XRF measurements for almost every element is attached.
copperSpectrum.png

Thanks guys, for your response.
 

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RJSakowski

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It would be an interesting project.

For an x-ray source, you need a gamma emitter. Apparently Americium 241 is the emitter of choice in ionizing smoke detectors and it is also used for XRF sources. It emits an 59.5 Kev gamma ray along with the alpha radiation.

There is some danger associated with amassing quantities of Americium 241 so caution should be exercised. If it were me, I would store the sources in a lead container and make sure that the XRF sources were well collimated in use.

This is all stretching my knowledge bank. I last dealt with anything like this over fifty years ago. What is the technology used in an x-ray spectrometer? Bruker, one of the leading manufacturers of XRF equipment, has a manufacturing operation in Madison, WI and a former colleague used to work there. I may have to have a talk with him.
 

graham-xrf

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OK - it appears that the "X" in "XRF" on the name does refer to X-Rays,a and many detectors do use a small X-Ray tube to make a pulse of X-Rays, very confined, and not going through the user.

ALSO - it seems, the thing works with stuff other than X-Rays, like Alpha particle emitters, and electron beams.
We discount electron beams, because you have to do the trick in a vacuum.

Here is where the smoke detectors come in. Americium 241 is an Alpha-particle emitter with a half-life of 432.2 years. The helium nuclei being emitted are at a level far below the background level, which is presumably why the levels measured when folk try going at smoke detectors with radiation detectors get much the same count no matter how far they strip it down.
--> LIKE THIS

The stuff is feeble, failing to penetrate a piece of paper. It shows on radiograph film from up against after 2 hours exposure. You can handle it. Just don't eat it!

We live on a naturally radioactive planet. The potassium in bananas is radioactive, and the sand from Chesil Beach in Dorset, as --> THIS Radioactive Beach in Brazil. Maybe nearly every shingle beach anywhere, but we are talking lots more than from a smoke detector.

Can you amass something harmful? Yes - but you have to try hard. Mixed with Am241 from about 100 smoke alarms + radium from old clocks + thorium from gas lamp mantles, purified with lithium from batteries, and a block of lead with a hole drilled part-way through.. sure, it becomes a breeder reactor which will make a mess.
ref --> David Hahn (no longer with us)
--> David Hahn Wiki
--> The Radioactive Boy Scout

Eight or ten or a hundred smoke alarms are not going to do anything nasty. There are a good deal more in most public buildings. You can expect there will be a portion of the population for whom anything beginning with "nucl" will rub on their beliefs kinda hard, but I try always to stay informed by the science.

The PhysicsOpenLab LINK DIY XRF provided by @homebrewed was really useful. (My thanks for that)

This is the sort of thing one can apply (say) a Raspberry Pi or Arduino to, and turn into a relatively affordable project, and I am sure there is enough expertise in HM to draw on. In a nice practical form, it could require some parts made in the shop, and at the end of it, you can know with some certainty which heat treat regime to use for the thing in the making. Know how hard will be the knife edge, of the gun barrel. Know from the get-go whether the steel you are using for whatever will resist corrosion. Know whether the bronze for the bearing is something other than a boat ornament.

Now that I look at it harder, it seems a safe an viable project that need not strain the finances and looks to be something that an HM member can do - and then post exactly how with plans and instructions in 3-part harmony!

It seems the "Theremino" part is a generalized USB interface to a PIC microcontroller.

MasterDIL-V5_3D_Top.jpg

MasterDIL-V5_SCH-1024x727.jpg

Perhaps this board could be side-stepped for not many dollars by using a $50 Raspberry Pi, and that is like an Arduino on steroids.! A full-blown computer (Pi-4) with all the operating system, USB, video, and GPIO connect pins one could want. You can even watch YT while you analyze steel.

I admit, I am tempted, but there is too much to get right on my house, my workshop man-cave in construction, and my two machines, to go at this one just yet, though I might just keep some of the parts I have around a bit longer.

- - - - - - - - - - -
P.S. Please note that there is no "XRF" allusion to anything related to my user name graham-xrf, where the "x" denotes "ex" like in "ex-girlfriend" and similar.
 
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RJSakowski

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OK, here's my take. The americium 241 is an x ray source. The x-rays from the source impinge upon the sample and electrons from the inner shells of the contained elements are knocked up to a higher shell. When they fall back to the lower shell from whence they came, they emit a photon (photoelectric effect) . The energies invoked are such that the photons are in the x-ray part of the spectrum. This is the fluorescence part.
Those photons hit the scintillation crystal and lower energy visible light photons are generated. The number of secondary photons is proportional the the energy of the original x-ray photon. Some percentage of those photons impinge upon the phoromultiplier which generates an electric current proportional to the impinging photons and thus proportional to the energy of the fluorescent x-ray. An electronic circuit measures the current for that original photoelectric event and records an event in a particular channel according to its energy. There are multiple channels, each of a different energy, and those are scanned after observing a sufficient number of events to generate the x-ray spectrum.

So, required components are: x-ray source, scintillation crystal, photomultiplier, and multichannel analyzer plus computer and software to display the spectrum.

When I was in college fifty years ago, we had a newly acquired multichannel analyzerin our nuclear physics lab. It had only about fifty channels and the readout was by columns of neon lamps. Digital calculators were almost a decade away and computers were mainframe affairs. I recall that we did some rudimentary analysis of gamma radiation with it.

Fast forward to 1997, I worked for a medical device manufacturer and we made products for calibration of diagnostic x-ray machines amongst others. Along that line, we made ionization chambers which measured x-ray energy by passing the x-rays through a chamber comprised of two parallel plates with a voltage applied to them. An x-ray photon passing through the chamber would eject electrons fro the contained gas, some of which would drift to the positively charge plate, generating a small electric current. This current was then amplified to generate a signal proportional to the energy of the x-ray beam.

I don't know if the signal from the ion chamber would be sufficient to feed a multichannel analyzer but it could, in theory replace the scintillation crystal/photomultiplier. If you think about it, a modern digital camera functions in a similar fashion arranging the "bins" spatially instead of by energy levels.
 

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The other approach for doing elemental analysis is EDX, energy dispersive x-ray spectroscopy. In this method an electron beam is accelerated to 5-30KV and focused on the sample. This basically replaces the x-ray excitation with e-beam. From there, a pulse height detector is used to generate the x ray spectrum, very much like the XRF system. The equipment is (naturally) expensive, so why would you go that route instead of XRF? Simple--spatial resolution. Your typical EDX tool is installed on a scanning electron microscope, which has very high resolution. Not needed to analyze a hunk of unknown alloy.

Back down to earth, I started wondering if it might be possible to update the old spark test by aiming a home-brew spectrometer at the trail of sparks and see what spectral lines show up. Here is a web site that sells inexpensive spectrometer kits.

Iron and carbon would burn and generate light but it's not clear to me if nickel, chrome, vanadium, molybdenum etc. would.

Again, even if the "new age spark test" scheme is able to detect the different metals in your alloy, it would be a challenge to get quantitative results. Still, it might be good enough to aim you in the right direction -- and if augmented with other data (magnetic/nonmagnetic etc) you MIGHT be able to narrow down the field of possibles even more.

An interesting discussion!
 

graham-xrf

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The other approach for doing elemental analysis is EDX, energy dispersive x-ray spectroscopy. In this method an electron beam is accelerated to 5-30KV and focused on the sample. This basiHe
2+
cally replaces the x-ray excitation with e-beam. From there, a pulse height detector is used to generate the x ray spectrum, very much like the XRF system. The equipment is (naturally) expensive, so why would you go that route instead of XRF? Simple--spatial resolution. Your typical EDX tool is installed on a scanning electron microscope, which has very high resolution. Not needed to analyze a hunk of unknown alloy.

Back down to earth, I started wondering if it might be possible to update the old spark test by aiming a home-brew spectrometer at the trail of sparks and see what spectral lines show up. Here is a web site that sells inexpensive spectrometer kits.

Iron and carbon would burn and generate light but it's not clear to me if nickel, chrome, vanadium, molybdenum etc. would.

Again, even if the "new age spark test" scheme is able to detect the different metals in your alloy, it would be a challenge to get quantitative results. Still, it might be good enough to aim you in the right direction -- and if augmented with other data (magnetic/nonmagnetic etc) you MIGHT be able to narrow down the field of possibles even more.

An interesting discussion!
A spark is a short-duration plasma
Suggesting one does it with a plasma instead of a spark- almost the equivalent of the Bunsen burner flame test, but much hotter, and with a wavelength detector (usually diffraction grating) to let you see more "colours".
OK - let us pick out the possibles.

To resolve first the X-Ray thing. Yes indeed, you can excite the metal atoms with X-Rays, but you can also use other primary excitation sources.

1) β- radiation is, as I understand it, an electron beam. It will do. β+ is positrons. We won't do that!

2) Protons. The stuff left over when we ionize hydrogen to get electrons. Hmm.. That is the stuff they use in the LHC. The hydrogen they use for many weeks supply is the size of a in-car fire extinguisher.

3) α Alpha particles. These are helium nuclei. 2 protons + 2 neutrons. Among other things, they come from smoke detectors. Written as He2+ or He2+ with energy 5MeV, and they move fast - like about 15,000 km/sec.

I can do, and have done X-Rays. Expensive, awkward to use, risky, needing high energy evacuated kit.

I once used a hospital X-Ray machine to put a beam through a 1mm thick little square of copper which I used as a neutral density filter to cut down the brightness of the beam, so I could develop an auto-focus video device for the photomultiplier display to allow continuous X-Ray diagnosis. The only way I could get my face close enough to the eyepiece was to sit on the machine, and let the beam go down onto the copper quite close to where I was ..er. sitting. I had the heavy white apron and all, but the beam was to the side of me, and I had it switched on for 20 seconds and longer at a time. X-Rays is not what we (OK - I) would want to use.

Electron beam guns is also something I have got to grips with. The up to 40kW kind where the beam is focused onto the top of the (titanium) being vaporized, using scan coil magnets to move it around. Huge vacuum pumps, and 35kV power supplies (variable), running up to near 1Amp. All is OK unless you lose control of the beam. If it ever hit the side of the chamber and broke through, that would be a huge dose of X-Ray.

I came to dislike electron beams. I still have two of the old Leybold Hereaus electron guns intact with cooling jackets and a high-isolation filament transformer. They are nice big chunks of beautifully shaped stainless steel that can be re-purposed. Alternatively, if any HM member wants them, even for a door stop or boat anchor, they are there for the taking, but you have to fund the shipping - and remember, I am in the UK! We can throw in the safety isolation filament transformer and a length of molybdenum filament wire. This stuff is a bit heavy.

We don't need X-rays, nor electron beams.
Americium is an Alpha (α) source, and a weak gamma (γ) source that is unknown in nature, the only artificially produced element, made by neutron bombardment of plutonium or uranium, so it is, in fact, a component of reactor waste. The tiny amount needed for a steel analyzer can come from a few smoke detectors.

Can we use the light as @homebrewed suggests?
Perhaps one can, though I think this is still the stuff of a small vacuum chamber. Perhaps of stainless pipe about 50mm diameter, and having quartz windows. A cheap plastic diffraction grating, and one of those "line array", or matrix photodiodes. The carbon arc can be started with a spark, stabilize the light, and the sample being tested is in fact one of the electrodes, or is placed on a piece of carbon. We only need a brief flare - perhaps 400mS.
The photodiodes can be sampled much faster, perhaps at 20 - 100kHz, and the outputs put through a calibration scaling before display. A Raspberry Pi fitted with an e-Bay A-D converter add-on board (about $10 to$40) might do.

So far, for me, this version is just a mad, free thinking, possibly stupid speculation. Like designing on the back of a napkin while the food is arriving! I have no idea whether this high speed, high tech, version of a Bunsen flame test will work. Feel free to trash the musings if you like.

The radioactive way - a proven design exists!
That is why I like it. None of the bits are outrageously expensive. Much of the design outline is already in this thread. It has some nice science in it.

How we get the spectrum plot out of it is something I did not quite understand. I (think) the energy that excites the metal atom is released as the electrons return to their un-hyped-up quantum state, and the wavelength of what is released is related to the wavelength by Planck's Constant, which is extremely er.. constant. So measuring the relative brightness of the scintillation leads to a place on the plot.

We surely do not need a build as clunky as this!

xrfEquipment3.png

The smoke detector set looks like this. Again, I am thinking it need not be like this.

xrfEquipment2.png

americiumSpectrum.png

OK - not fully checked out yet, but this last option looks so very feasible that it is surely worth a scrutinize by HM Forum crowd critique.
 
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hman

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Hmmmmm ... high voltage power supply for the photomultiplier .... Maybe this one?

-or-

use one of the Rooshin night vision scopes! They include photomultipliers (though an imaging type).

(2) One thing I think I missed in your description of a DIY XRF rig was a monochromator - something to separate the frequencies of the detected radiation, so you get a spectrum, as shown in your illustration. Your most recent post touches on that, but I don't think brightness and wavelength/frequency are interchangeable. RJ's explanation helped a little, but I still don't "get it." My studies in chemistry did not include XRF or EDX. The closest I came was in grad school, where I did ESCA spectroscopy. That entailed analyzing the energy spectrum of electrons emitted when a sample was bombarded by Xrays. Electrons aree a WHOLE lot easier to manipulate than photons!

(3) Good thing you mentioned "P.S. Please note that there is no 'XRF' allusion to anything related to my user name graham-xrf, where the 'x' denotes "ex" like in "ex-girlfriend" and similar." I was really starting to wonder!
 
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graham-xrf

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(2) One thing I think I missed in your description of a DIY XRF rig was a monochromator - something to separate the frequencies of the detected radiation, so you get a spectrum, as shown in your illustration. Your most recent post touches on that, but I don't think brightness and wavelength/frequency are interchangeable. RJ's explanation helped a little, but I still don't "get it." My studies in chemistry did not include XRF or EDX. The closest I came was in grad school, where I did ESCA spectroscopy. That entailed analyzing the energy spectrum of electrons emitted when a sample was bombarded by Xrays. Electrons aree a WHOLE lot easier to manipulate than photons!

(3) Good thing you mentioned "P.S. Please note that there is no 'XRF' allusion to anything related to my user name graham-xrf, where the 'x' denotes "ex" like in "ex-girlfriend" and similar." I was really starting to wonder!
OK - we step carefully here - why we don't need a monochromator. All spectrum analysis of the various frequencies light kind do need it. Diffraction gratings, Fresnel things, anything to bend the light varying amounts depending on the color.

We are finding out the unique wavelength - or frequency if you like, of the light emitted from an element. We are hitting it with radiation energy, albeit not from a Bunsen flame, nor a spark. We use a radioactive energy.

Now here is where we get right into the murky waters of "is it a particle, or is it a wave"? There are now lots of good explanations on the equivalence of matter and energy, and the "Quantum Standard Model". The quantum model is an elaborate scientific fairy story which does not care that the concepts are arbitrary and non-intuitive. What is known is that it allows exact calculation and prediction to better than 10 digits of extraordinary, repeatable precision.

When that "energy", whether thought of as a helium atom with momentum, or simply as a bunch of energy, slams into the metal, the electrons in the atom will only accept strictly discrete amounts - i.e."quanta", and after a short time, from nanoseconds to hours, depending on material, the electrons drop back to their previous state, releasing back exactly that amount of energy.

Now we get to the nice bit. That energy comes out as radiation - photons - it is light. It zips away at the speed of light. And best of all, it has to be a unique color. At this point, you can say "ahh - we can figure what element that came from is we use a monochromator grating, and make it sit at it's place in a spectrum. This could be done if one was madly energising it, like the phosphors in a flourescent tube.

As I understand it, this method is different. The photon that is released hits a scintillator material where the whole excitation thing happens all over again, but this time in a constant, known, material. So the now second-hand light from the scintillator crystal excites a photomultiplier tube, or photodiode, or maybe solid-state photomultiplier. It results in an electric pulse which can reveal meaningful information. The nature of the pulse, the timing, the slopes, and the magnitude of it, are a signature of the metal that started it all.

I am not an expert. I am still reading up on exactly how this trick works. A whole bunch of metals in the mix can apparently produce a whole bunch of little slopes in the response, unique to each, and the magnitude of the departures can indicate relative proportions. The math, and science in this is not trivial, and is completely contrary to the reasonable simple, low cost kit that is involved.

The XRFSpec_ENG.pfd file posted earlier in this thread has the pulse data signatures for nearly every element.

OK on the "xrf" in my username. It was pure coincidence!
 
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graham-xrf

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Maybe a silly question, but if you dissolved the metal in acid, and shine a wideband filament type light through it, and then spread the light with a grating or prism, would you see a "dark line" corresponding to the absorption of light wavelength specific to the stuff in the solution?

Yeah - I know, if it was that easy, it would be widely done already!
 

RJSakowski

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Alpha particles have to be accelerated to a very high velocity in order to generate x-ray fluorescence in a target. This would require a linear accelerator. In addition, the beam would have used in a high vacuum. The Americium 241 source emits a relatively low energy alpha particles, easily stopped by a few sheets of paper. It is the 59.7Kev gamma ray that is responsible for the fluorescence in target materials. The fluorescence photons re not light. They are much higher in frequency , above UV and in the x-ray region where their "frequency" is measured in terms of energy( e =hf).

To detect these x-rays, they are passed through the scintillation crystal where again the photoelectric process takes place and visible light photons are generated. The sum of the energies of the photons generated is equal to the energy of the x-ray photon.
 

RJSakowski

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Maybe a silly question, but if you dissolved the metal in acid, and shine a wideband filament type light through it, and then spread the light with a grating or prism, would you see a "dark line" corresponding to the absorption of light wavelength specific to the stuff in the solution?

Yeah - I know, if it was that easy, it would be widely done already!
Actually, you do not see a single line. If you run a spectrum of the light passeing through the solution it is a rather broad absorbance band. Offhand, I can't give you the physics of it but I have run enough of them to know it for a fact. Additionally, the colored solution resulting from absorbance is not dependent on an interaction with the nucleus. Copper chloride is a different color than copper nitrate. Add ammonia, and the solution turns a very intense blue.

It is possible to see absorbance lines (Fraunhofer lines) if the matter is in a gaseous state. This is how the atomic absorption spectrometer works.
 

graham-xrf

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Alpha particles have to be accelerated to a very high velocity in order to generate x-ray fluorescence in a target. This would require a linear accelerator. In addition, the beam would have used in a high vacuum. The Americium 241 source emits a relatively low energy alpha particles, easily stopped by a few sheets of paper. It is the 59.7Kev gamma ray that is responsible for the fluorescence in target materials. The fluorescence photons re not light. They are much higher in frequency , above UV and in the x-ray region where their "frequency" is measured in terms of energy( e =hf).

To detect these x-rays, they are passed through the scintillation crystal where again the photoelectric process takes place and visible light photons are generated. The sum of the energies of the photons generated is equal to the energy of the x-ray photon.
Yes - and I should have seen it earlier. The spectrum for AM241 in post #15 shows it has the 59.7keV emission line on the right, which is enough to excite the K and L lines of all the elements.

I am guessing it it is the role of the scintillator crystal material to capture these beyond-visible wavelengths, and re-emit light photons into a photo-multiplier or other technology detector. It must be a special effect, and not just from excitation of it's own elements.

Thanks also for the explanation of experience with solutions. I did think that route would have some downsides.
 

RJSakowski

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Yes - and I should have seen it earlier. The spectrum for AM241 in post #15 shows it has the 59.7keV emission line on the right, which is enough to excite the K and L lines of all the elements.

I am guessing it it is the role of the scintillator crystal material to capture these beyond-visible wavelengths, and re-emit light photons into a photo-multiplier or other technology detector. It must be a special effect, and not just from excitation of it's own elements.

Thanks also for the explanation of experience with solutions. I did think that route would have some downsides.
Here is a fairly thorough explanation of the scintillation process.https://en.wikipedia.org/wiki/Scintillator
 

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RJ- I thought you were just a fisherman!? But wow! You guys are very impressive. However, I am not at all shocked that we have this kind of talent on HM! This is a very interesting project that I would like to hear more about. I have always wanted an XRF since I got into casting (metal, not trout.)
I am staring at a photomultiplier tube from a scrapped gamma camera. I think I have some Americium in the basement. Is this really possible? Talk about a quarantine project!
Robert
Edit: I believe all the current gamma cameras are solid state detectors. Is that an option?
Robert
 
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hman

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Graham -

Thanks for your explanation. I really goofed when I said "monochromator" ... actually meant to ask about way to distinguish the wavelength/energy of the fluorescence (Xray) photons. Your mention of a spectrum analyzer did set me straight. Bottom line, though, is that I'm an old geezer and sometimes kinda dinosaurian in my thinking. Ah, well ...
 

graham-xrf

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Graham -

Thanks for your explanation. I really goofed when I said "monochromator" ... actually meant to ask about way to distinguish the wavelength/energy of the fluorescence (Xray) photons. Your mention of a spectrum analyzer did set me straight. Bottom line, though, is that I'm an old geezer and sometimes kinda dinosaurian in my thinking. Ah, well ...
Old geezer me too, but I nevertheless am still surprised and irritated when the stuff that reminds us of it gets in the way of a bit of "growing old disgracefully".

As I understand it so far..

1. You start with some of these smoke detector sensors. Here is one I extracted from an old smoke detector.
(Yeah - nearly live. On the desk in front of me. Making a mess!)

Not that I expect any Brownie points from HM for doing this in their cause, but I am very aware that I am handling a by-product of plutonium decay that is a fissile material with a large neutron absorption cross section 5700 barns (yes - as in "big as a barn door"), which gives it a critical mass of around 9kg to 14kg. This is not quite what I mean when I say "growing old disgracefully, but you get the idea.

That said, the amount in there is around 2.62E-7g or 262 nano-grams. It is in the little pressed metal setting "button", which comes out and bounces on the desk, and makes it to the floor, and ..yeah!

Americium Dioxide Smoke Detector.jpg

Of course, the great YT resource shows it much better than I can, and one in particular comes with fun sparks and zap stuff..
--> How Radiation Works using Americium 241, Alpha Particles and Gamma Rays

and another where at about 3:05, we actually see the radioactivity measured (no gloves)
--> Extraction of Americium 241 from Smoke Detector

It occurs to me that one might get up an effective source from grinding up a Coleman lamp gas mantle. You can get the thorium version, which work better than the yttrium type as lamps, from eBay.

2. We arrange the Am241 buttons in a circle, around a shield tube end. The radiation from the buttons strikes the metal under test, and out comes photons you can't see, back at the detector in the middle of the tube. Yes - the energy that exits the metal atom does have a wavelength, and it might not be at some convenient visible (wavelength).

3. It hits the material of a scintillator material. A crystal of cesium iodide.
They come at all sorts of crazy prices asked, from USA to Ukraine, from 20 bucks to a couple of hundred $$.
Like this --> eBay CsI

Now we discover there are various scintillation materials, like Na(TI), and every kind of combination fitted up with detector photomultipliers, etc. I have not explored this enough, but know that the electron tube type is the only sort that can get down to the lowest energy detection without generating a lot of competing electrical noise.
The flash given off by the scintillator material is proportional to the photon energy arriving.
I like the Hamamatsu tube with the cesium iodide scintillator already bonded to the tube.

4. The light pulse triggers electrons from a photo-sensitive cathode in a photomultiplier tube. The nature of the thing is to produce in proportion, perhaps up to a hundred million more. An electrical pulse, which can be measured. Clever gadget, but the circuits are simple.

1024px-PhotoMultiplierTubeAndScintillator.svg.png

500px-PMT_Voltage_Divider.jpg

This is, so far, the most expensive part. It is also the place where we get the most variety in DIY approaches. You don't have to get this particular one. The majority of enthusiasts out there are looking to make radiation detectors of various kinds. They want the clicks, and the meter showing the counts per second rate.

What we are after is more subtle. We want to measure the pulse height, duration, and shape.
That is - I think so. Everything I read looks to be about that.

Hamamatsu Photomultiplier.png

5. If you are still with me so far, this amounts to some fairly simple, and not too expensive kit, given that we are trying to make a nondestructive point-and-shoot general materials detection and analysis gadget.

According to the link from @RJSakowski , the Wikipedia on Scintillators, you get a pulse. The stuff is very much hard sums about scintillation science, but it is worth scanning even the indigestible , just for perspective.

6. Measuring the pulse(s).
This is where we need not get all entangled with old project stuff like the "Therimino" thing. I have not yet untangled it all, but it seems they were using the audio input microphone channel on a computer to sample the signal as a 192kHz A-to-D converter, in the same manner as ham radio enthusiasts would contrive to make spectrum and waterfall displays of signals. They also had a PIC micro-controller USB adapter.

I think it is a series of pulses from each scintillation, triggered, sampled, and averaged.

I have not yet figured it all out, but I am thinking that yes - one could use the audio channel as a signal waveform sampler, though my preference would be something more made for the purpose, such as a dedicated A/D converter instrumentation card. Or use the Audio channel. Either way, all you need for final hardware is £35 or so of Raspberry Pi, or Arduino. It could even be a smartphone app.

I freely admit I have not got it all figured out yet, but a steels alloys analysis without breaking the bank seems kind of possible
 
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graham-xrf

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Edit: I believe all the current gamma cameras are solid state detectors. Is that an option?
Robert
Robert: No, I don't think so. What the detector can do depends on the scintillation material. You can get gamma detectors in several technologies.

The ranges of energies, and wavelengths that solid state (Si) detectors can do seems to have a lower end that is electrical noise limited - that the thermal noise from molecules wiggling about as in any semiconductor material. The electron tube types can apparently work at low noise to much lower levels.

Again - I am in the "soak-up" phase of learning much of this science. When I know enough to give a better answer, I will say what has been shown to be so, and who says, and so on.

I am less into fully getting to all the theory expounded , and more into wringing out the practical stuff one needs to make something like this work. I am not at all sure I am up do doing something like this all by myself. I may need some help. You can be sure that if I get to the point of getting up a working, proven verified, demonstrable build, then it will be posted here, with all the instructions.
 

RJSakowski

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It looks like you are getting the hang of it. In bullet 1., I wouldn't mess with the Th 232 It has a much longer half life, 1.39e10 yrs. compared to 275 yrs for Am 241 which it will be a much weaker emitter/gram of material. Also, the largest danger with alpha emitters is from ingestion. Although they are extremely short range, alpha particles are extremely active. Any process that would have the potential of creating small particulates should be avoided. In contrast, the AM 241 is in the form of a pellet and and can be used that way which minimizes any potential ingestion risk. As I see it, the form found in smoke detectors is ideal for this application. Think of the array light a camera light, illuminating the target. If mounted on a lead backing plate, all of the beam will be directed forward toward the target with almost no radiation from the source interfering with the desired signal.

The combination of scintillation crystal and photomultiplier make up a radiation detector. As I recall, radiation detectors operate in three distinct modes, the Geiger region, a proportional region,and the avalanche region. Which region of operation you're in is determined by the mukltiplication rate of the individual dynodes in the multiplier which is controlled by the potential difference between the dynodes.

For a pulse height analyzer, we want to operate in the proportional region. In this region, the output current generated by each event will be proportional to the energy of the x-ray photon.

From there, we need to sort out the energy, as represented by the output current. I expect that this could be done by converting the current signal to a voltage and using an A/D converter to create a digital value. A gate would activate the A/D converter and lock out any additional input while the pulse information was being processed. The processing could be done by a series of conditional cases in the program sorting the event into an appropriate accumulator array and the array would be scanned to provide the count vs. energy display. The processing part would need to fairly fast to minimize dead time and loss of events. From my experience, the events aren't to closely timed, at least with fairly weak sources. The energy spectrum would be built up, pulse by pulse until it was reset and displayed on some suitable output device.

A simpler scheme would be look at a single energy, knowing that a particular element would be emitting x-rays at that energy. A fairly simple pair of comparators could define the voltage box, V1< Vsample< V2, and if the sample voltage is in the box, a counter is incremented. Ideally, You would compare the signal to a background signal and calculate the ratio. The ratio would be compared to the ratio from a known sample to give a thumbs up or down to the identity.

It would seem that we have existing devices that could be hacked. I have an app on my Android phone called Physics Toolbox Suite which has, among other interesting tools, an audio spectrum analyzer. It is sorting a real time audio signal into a frequency spectrum which can be frozen.
 

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@RJSakowski :
Entirely agreed. I did say we should not eat the stuff! The bits of fragile (used) thorium mantle sticks to fingers, and floats about in the air, and generally much harder to control until one gets it held down somehow.

That said, the smoke detector little "button" did it's best to become inaccessible. I had to crawl around on the floor, looking all over the place to retrieve it. After all - it might eventually become 1/8 of my steel alloy sensor!

Now that we are beginning to figure this out, even to the extent of a design of our own, it is maybe time to look at the wish list of features. Can we aspire to know more than which elements are present? Might it deliver approximate percentage proportions? Is it, or need it be battery powered? Is it a gadget with a USB lead to a smartphone app? Are there any low cost Silicon photodiodes that might do the job?

This needs a pause for HM contributions. Feel free - no matter how critical, or crazy. If it is just clouded by wishful thinking, I am happy to blame the lockdown effect!
 

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Scintillators and PMTs aren't used in commercial EDX tools these days. Instead, they use large-area silicon detectors, basically high voltage diodes. As in the case of a scintillator/PMT, the pulse height is proportional to the x-ray photon energy. That, by the way, is what "EDX" stands for -- energy dispersive x-ray spectroscopy. There is another approach that uses a crystal as a kind of diffraction grating, where the grating is the crystal lattice itself. As the crystal is rotated the incident x-rays are diffracted at different angles toward a fixed detector. Very much like a visible-light monochromator. This type of system offers much higher resolution but, because it acquires one wavelength at a time, it is much slower. Also, you STILL need some kind of detector. This type of system is called a WDX, or wavelength-dispersive x-ray spectrometer. Our old WDX used an ionization detector, a lot like a Geiger tube -- but IIRC the active gas was either a mixture of methane or carbon monoxide (!).

Also check these links out: http://www.noah.org/science/x-ray/detector/ https://benkrasnow.blogspot.com/2012/11/large-area-detector-for-x-rays.html ; and you might be able to acquire some of the hardware here. I haven't gone so far as to check prices from the latter so it still could be out of the range of what hobbyists would be willing to pay.
 

RJSakowski

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@RJSakowski :
Entirely agreed. I did say we should not eat the stuff! The bits of fragile (used) thorium mantle sticks to fingers, and floats about in the air, and generally much harder to control until one gets it held down somehow.

That said, the smoke detector little "button" did it's best to become inaccessible. I had to crawl around on the floor, looking all over the place to retrieve it. After all - it might eventually become 1/8 of my steel alloy sensor!

Now that we are beginning to figure this out, even to the extent of a design of our own, it is maybe time to look at the wish list of features. Can we aspire to know more than which elements are present? Might it deliver approximate percentage proportions? Is it, or need it be battery powered? Is it a gadget with a USB lead to a smartphone app? Are there any low cost Silicon photodiodes that might do the job?

This needs a pause for HM contributions. Feel free - no matter how critical, or crazy. If it is just clouded by wishful thinking, I am happy to blame the lockdown effect!
You need a scintillation detector to find those wayward buttons.

The PHA we have been discussing are capable of measuring quantity provided there is a means of calibration. The easiest way would be to have a known sample.
 
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