Needing more than a spark test?

Assuming that the excitation source is going to be a ring of Am 241sources, the fluorescence x-rays will be a fairly diffuse region. As such, it would seem that an integrating sphere will less beneficial. I would think that you would want the target material to be in close proximity to the scintillation crystal. I would also think that you would want the scintillation crystal to be in close contact with the detector. The surfaces of the scintillator could be coated with a reflective coating with the exception of the window to the detector to maximize capture by the detector. I would suggest aluminum foil for the window to the sample. The side geometry needn't be thin and there would probably be an advantage to using a high Z material to prevent fluorescence from the target x-rays interacting with it. Gold foil as used for gilding purposes may be a good choice. Presumably the sides of the crystal will be further shielded with lead to prevent source x rays from entering the crystal.

I would think that the scintillation crystal would be thicker rather than thinner to permit greater interaction of the fluorescence x-rays.
 
All open questions that only experimentation will reveal. Not having done ANY experiments yet, I freely admit that I'm whistling in the dark... Graham will likely be the first to have some results and that will be interesting to see. I'm interested in an experimental platform that allows exploration of some of these ideas, and that could take some time to work up.

I'm still working on getting the garden in -- so progress, if any, on my part will be slow for some time to come. Summers around here are short and precious!
 
From the pictures in post #182, in set #7 (Good Grieff - that many?), you can see how deep is a standard Na(Tl) crystal.
Also see that it is enclosed in a little aluminum can. The clear end goes up against the PMT detector.
Any incoming X-Ray photons had to go through the aluminum - which apparently it can do with ease.

@homebrewed : If you are committed to, or have purchased a particular Si(PM) avalanche photodiode, then do tell, so I can get the same.

For me - not garden, but it feels like it. Clearing ground the manual way for the concrete hardstand. The foundation footings do not have to be very large for the relatively small walls, but it is still hard going! When it becomes possibly to hire a dinky digger again, I might go for it!

Now that I have tapped into a little of what Lucian does, I have much respect for what he knows.
 
I am planning on getting the KETEK 3x3mm PM3325 demo board. It has 25um^2 cells and has somewhat higher photo detection efficiency than the PM3315 (better fill factor???) but has the same dark count -- 125K/mm^2 at Vov=5V. It should be easier to adapt for our purposes compared to the ON Semiconductor version. Plus, it should be easier to stick a Peltier on the back if temperature control becomes necessary.

Hopefully we don't need to sweet-talk KETEK into selling their modules to mad scientists :D
 
Back to the idea of coating a scintillator crystal with a reflective layer. I continue to think that a significant increase in collection efficiency will result in a noticeable improvement in XRF resolution.

Tollen's reagent is used to test for the presence of sugars, being signaled by the deposition of silver on the sides of a test tube. I never did this one in college chemistry but it's a classic. Don't want to buy all the chemicals to deposit a small amount of silver? You can buy mirror-silvering kits here for not a lot of money. This approach is not compatible with hygroscopic or "slightly hygroscopic" crystals, so CsI(Tl) is not a suitable choice. The substrate has to be scrupulously clean in order to get a good silver dep. The same vendor sells kits for applying aluminum metal leaf, but the "glue" is gelatin dissolved in water so, again, not suitable for hygroscopic crystals. It could be a challenge applying leaf to a relatively small crystal. I have a cheap BGO crystal I could experiment with.

I have an inquiry in to AngelGuilding regarding the thickness of the chemically deposited silver and aluminum leaf. Since they're into the art side of this, they may not know. From my experience with silver dep, it is pretty thin. Fortunately, silver's K-alpha line is a long way away from Cr, Mn, Fe, Co and Ni so it wouldn't interfere with the analysis of ferrous alloys. And, while silver is readily tarnished, it also is my experience that the inside of the silver layer stays nice and bright....which is exactly what we want.
 
Did I read it wrong? I thought Na(Tl) was the bad one for hygroscopic. Cs(I) was "slightly" hygroscopic. That was the kind Lucian cut through. It also begs the question of how you get the water out of them in the first place. Heat? Vacuum? Never?.

One can find boxes of Na(Tl) units on eBay, where the seller carefully describes the yellowing condition of some, and which ones have the "bubble" in them, presumably a water boundary. I rate these as unusable, but it begs the new question, "do they work in any fashion at all"? Can they be recovered - after all, they still have all the correct elements present.

Best of all - I like the idea of plastics that scintillate. No need to "grow" the crystal. It brings the new question. Acrylics are not crystalline (I think). Heat them up and they melt. Is the business of making them scintillate a matter of "stirring in" whatever additive stuff scintillates and letting it cool? Will someone with a UV light point it at perspex? Does it need to be UV(B)?

We now know that in almost any field, any question we may have, and any idea we might cherish, has a high probability that someone has already been there! Somebody, somewhere, already knows!
 
Polyethylene Napthalate (PEN)
Wikipedia states this plastic scintillates so well it is expected to replace classic plastic scintillators.
It begs the question why it has not done so by now!

Used industrial food packaging, durable films and adhesive tapes, flexible circuits material, plastic drinks bottles, tyres, and more.

Made by DuPont, Toray,Teijin, BASF at least.
(You have to imagine trying to explain oneself dumpster-diving or raiding plastics recycle bins with a UV light)!
What might be the chances of liberating some of this stuff?
 
Silica drying beads can be rejuvenated by baking them in an oven @250F for a few hours. I've done it and it works (you can tell because the beads usually have a little bit of cobalt chloride in them, which changes from blue to pink as it transitions from "wet" to "dry").

I've read that copper (1) iodide may be a good material for use in plastic scintillators -- see here. I'm not aware of anyone selling the CuI complexes so it probably would be necessary to roll your own. Pyridine is toxic and apparently really noxious so I would look into the triphenylphosphine -- but would need to look into its toxicity, too. There are a number of organophosporous compounds that are extremely toxic, featuring in things like insecticides and nerve gas (think Phosgene). I also found a paper here that describes scintillation properties of CuI single crystals and powder. So one possibility would be to buy or synthesize copper(+1) iodide and make a plastic scintillator with it. I found someone on ebay selling 99.995% pure CuI, $38.12 for 25g.
 
graham-xrf said:
Polyethylene Napthalate (PEN)
Wikipedia states this plastic scintillates so well it is expected to replace classic plastic scintillators.
It begs the question why it has not done so by now!

Used industrial food packaging, durable films and adhesive tapes, flexible circuits material, plastic drinks bottles, tyres, and more.

Made by DuPont, Toray,Teijin, BASF at least.
(You have to imagine trying to explain oneself dumpster-diving or raiding plastics recycle bins with a UV light)!
What might be the chances of liberating some of this stuff?
Click to expand...
It would be interesting to experiment with. There are some indications that plastic scintillators may not be very good for detecting low-energy gamma/x-rays -- take a look at this: open-physics plastic scintillator test. They describe an attempt to see the 59Kev gammas from americium, which was a bust. Doesn't bode well for the ~6Kev photons we're interested in, although the plastic should be somewhat more absorptive compared to the primary gamma (a built-in energy filter???). A composite detector, plastic + high-Z scintillator powder, might work better. It IS interesting that they are using a reflective wrap around the scintillator to increase the light collection efficiency. Their approach looks simple but effective.....right up my alley.

Don't buy PEN from Goodfellow -- they want an arm and a leg (maybe more) for their stuff. I can't believe how expensive EVERYTHING is there. They sure aren't selling to hobbyists.
 
homebrewed said:
Silica drying beads can be rejuvenated by baking them in an oven @250F for a few hours. I've done it and it works (you can tell because the beads usually have a little bit of cobalt chloride in them, which changes from blue to pink as it transitions from "wet" to "dry").

I've read that copper (1) iodide may be a good material for use in plastic scintillators -- see here. I'm not aware of anyone selling the CuI complexes so it probably would be necessary to roll your own. Pyridine is toxic and apparently really noxious so I would look into the triphenylphosphine -- but would need to look into its toxicity, too. There are a number of organophosporous compounds that are extremely toxic, featuring in things like insecticides and nerve gas (think Phosgene). I also found a paper here that describes scintillation properties of CuI single crystals and powder. So one possibility would be to buy or synthesize copper(+1) iodide and make a plastic scintillator with it. I found someone on ebay selling 99.995% pure CuI, $38.12 for 25g.
Click to expand...
With normal care, we should not be be unduly put off by "toxicity ". There is a difference in something being violently toxic, and it being an unmanageable hazard. Most stuff in the shop is toxic, even the bit of copper, and my bathroom store has at least two bottles of presidential strength thin bleach!

Pyridine has a fishy stink, which means someone at least survived smelling it. William Ramsay cooked up acetylene and hydrogen cyanide in red-hot iron tubes to make piridine when he was 22, and survived to pick up his Nobel prize in 1904 (for other adventures with Argon, Neon, Krypton, Xenon, and for isolating Helium). Maybe it was sniffing piridine that contributed to the nasal cancer which ended him.

I agree that for convenience we try for harmless stuff. Recyclable plastic bottles of PEN without paying Goodfellow appealed to my nature, and even supplies some warm feeling about re-using good plastics.
 
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