Needing more than a spark test?

graham-xrf said:
There may well be good suggestions.
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If it turns out that using energy filters will be needed to improve the system's ability to distinguish different ferrous elements, it might be desirable to design-in a rotary shutter to switch in different filters. It could be done manually as well, but, again, it would be nice to have something set up to make it easy. I had a darkroom projector which had a slot that could accept different filters (typically to use in combination with variable contrast printing papers) and that made it very easy to use them. It was all manual, but, hey, the projector was made in the 70's.
 
"The thought occurs that the entire plot without sample present could be counted, then subtracted from the plot when the real material is present. in the same way that dark current noise is removed from CCD images."
I like this idea. Very clever.
Homebrewed- can you elaborate on the need for filters? How and why would that work?
Robert
 
homebrewed said:
If it turns out that using energy filters will be needed to improve the system's ability to distinguish different ferrous elements, it might be desirable to design-in a rotary shutter to switch in different filters. It could be done manually as well, but, again, it would be nice to have something set up to make it easy. I had a darkroom projector which had a slot that could accept different filters (typically to use in combination with variable contrast printing papers) and that made it very easy to use them. It was all manual, but, hey, the projector was made in the 70's.
Click to expand...
This does not present a problem. The scatter-gun optics of 60KeV photons mean the arrival angles are not critical, but here, I take it you mean the 60KeV has to hit the sample before the emanated X-Rays have to go through the filter. Convenient if the filter was transparent to gamma, one could put the filter over the sample. More tidy, and smaller, is to have a filter disc to push onto the iris tube, or up the tube, right in front of the sensor. If glued into it's carrier, one needs to make sure the glue elements do not see any 60KeV - or otherwise stay with it peened into fundamental materials.

@rwm - Hi Robert. The filters trick is Mark's. As I understand it, one can put discs of various materials that will absorb or be transparent to ranges of energies corresponding to various alloy elements as a way of identifying them, and the proportions present. You might also suppress the iron signal, and see what's left.

There is also a "software" version of this. If the return pulse energies are sampled accurately enough, and with sufficient repeatability, the energy step between the count accumulator buckets can be set for higher resolution, and even plotted "spread out" over a smaller range, hopefully to show the alloy peaks as separates, and even allow a compute of their percentage as scaled by 100% being the total count of all element's buckets seen. One might simply set the counts of various known energy buckets to be zero, which is a brutal subtraction filter, to allow identification of the other stuff in there.

A rotary filter changer would be very fancy. Keeping it simple by putting a filter in by hand might be OK.
 
The energy filter scheme isn't my idea -- like most things, someone else thought of it long ago. It's based on an abrupt change in the absorption curve of a material, as shown here:
Manganese xray apsorptivity.png
If we choose a material that has an absorption edge between x-rays coming from two elements that are otherwise difficult to distinguish, this abrupt change can be used to improve the effective resolution of the system. In the case for Mn, it can be used to help distinguish iron from cobalt. It turns out that by using the same adjacency relationship (on the periodic table) of using Mn to help analyze Fe and Co, we can use an iron filter to help distinguish Co and Ni, and so on -- at least, in the ferrous materials. I haven't looked to see if this works for nonferrous elements.

The ability to separate peaks using energy filters improves as the thickness of the filter increases: but the overall count rate also decreases, so there's a limit to how much improvement can be achieved in a practical application. A combination of filtering plus the use of pure reference metal spectra (to subtract from the unknown's spectrum) may be the best approach. But until we have a few operating XRF systems we really don't know, do we.

Regarding the use of an automated approach to swap in different filters, I was getting WAY ahead of what needs to happen first. Something like that would be desirable for a commercial product but overkill for a hobbyist-level thingie. Scratch that suggestion.
 
I don't know if we mentioned it before but that absorption edge is frequently referred to as the "K edge." So the filter would effectively subtract out some of the counts from the lower eV materials photons?
Robert
 
Even if the count is lowered through a filter, the X-rays that do make it through are undiminished. They will still end up in the Fe or Co buckets. We can use an absorber as thick as practical. We might only have to wait more seconds if the filter is present, and the software can change the time of the test sample duration based on the fact a particular filter is there.

.. Calibrated by using a piece of Kosher (??) iron with and without the filter - maybe!

If one suspects there may be a particular element in the alloy, but at a low count - or even if the identification algorithm sees a combination that suggests the element should be present to complete a high probability identification, then all buckets except for the energy range corresponding can be shut down, and the guessed at element "looked for".

I think I shall increase the number of sources to 8, because I think more is better, and the octagon version of tilted pockets is easier to drill.

Can anyone suggest a machining procedure for my version of a sensor head. Given the "all directions" nature of 60KeV gamma, would it not just be simpler to drill the pockets parallel to the axis, and still have it work OK? I was trying for a sensor head as compact as possible. Some of my first thoughts had it about the diameter of a paint can. This kit can work OK, for larger sample shapes, with a push-on funnel-type tube extension.

I wonder how it would do with a container of liquid as a test object?
Does not X-Ray energy signatures also work for chemical groups - or is that a strictly infra-red thing?
Would having a alternative connectable sensor head with a small filament lamp source, and a IR detector photodiode, but retaining a switched-in version of the electronics and software parameters have it change it's spots into becoming a FTIR substances analyzer?

(Sorry - I caught the "getting WAY ahead" bug :) )
[Edit: Also not sure one can have Kosher, Halal, or any other kind of religiously approved Iron ]
 
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Your head design is elegant, but I do not think the sides need to be angled in concave fashion. As you note, the photons are emitted in all directions. I think flat would work just fine and simplify machining. I would keep them as close to the center radially as possible to excite the smallest area of the test sample with the largest number of gammas.
I don't think xray signatures would work like IR spectroscopy but you could identify elements in solution. It will be interesting to test with iron, silver or copper solutions.
Robert
 
rwm said:
Your head design is elegant, but I do not think the sides need to be angled in concave fashion. As you note, the photons are emitted in all directions. I think flat would work just fine and simplify machining. I would keep them as close to the center radially as possible to excite the smallest area of the test sample with the largest number of gammas.
I don't think xray signatures would work like IR spectroscopy but you could identify elements in solution. It will be interesting to test with iron, silver or copper solutions.
Robert
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OK - I will post a changed design soon. Right now, I am also up to my ears in domestic stuff, but I am feeling much more positive since I got vaxed. Shot full of what turned out to be Pfizer's best biotech is definitely the way to pick up the mood. I still have to wait for the second, and the easing of restrictions before I can take care of a bad case of "lockdown hair".

I have in mind to move the A/D converter on, then make up some kind of lash-up head to fully develop the low noise amplifier signal conditioning. I know which amplifier I want, but I am seeking something perhaps nearly as good, but available in a package size that gives us a chance for electronics assembly. If we can get the bits big enough, and the assembly instructions expansive enough, it might bring the making of this stuff to the point where many folk who would not usually attempt to put together electronic stuff be able to "have a go".
 
At some point you guys need to change the thread title to Shop Built XRF! Maybe after the first successful sample test? This thread will get sent all over the internet and have a million hits. Just look at the views on my Oil Can thread.
I am def gonna build this when you finish working it out.
I also got my Pfizer doses a few weeks ago. I am still being somewhat careful since my wife can't get vaccinated.
Robert
 
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