Needing more than a spark test?

graham-xrf said:
Not really. It is a gamma detector.
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Not sure what you mean. Do you mean because it won't detect energies low enough?
I did find specs on some of the Hamamatsu's that say they detect down to 30 KeV efficiently. We would obviously need to be at and below that number (down to 1KeV?) I am not sure how bad the detector signal would fall off below 30 KeV. It is kind of attractive to find a brand new detector for $20 if it could be make to work.
Robert
 
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graham-xrf said:
Roll your own (scintillators)?
I was just reading Wikipedia on organic, and then plastic scintillators.

Napthalene:
Smelly stuff, anisotropic with problems of energy resolution - but hang in there for now. It gets used.

Polyethylene napthalate:
This is sailcloth and drinks bottles plastic. Scintillates by itself without adding other fluors.
"Is expected to replace existing plastic scintillators due to higher performance and lower price".

Base plastics + fluors
Polystyrene:
As a base. A good thing for which to melt down those non-degradeable transparent disposable spoons.

Polymethylmethacrylate (PMMA):
i.e. Acrylic has advantages. High ultraviolet and visible light transparency. Transparent to it's own radiation.
Add some napthalene with the solvent.

Fluors wavelength changers.
Used to catch UV and render it visible blue or green. Generally yuk polyphenyl hydrocarbons, but only needed in small amounts. I would not know how to come across oxazole or n-terphenyl (PPP).

I would not be past melting up up some acrylic or polystyrene, stirring in some re-purposed mothballs, making into a scintillator and a taper lightpipe all in one. Like all simple-sounding schemes conjured in ignorance, this notion may have some downsides, but is the idea completely mad?
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I had looked at organic scintillators as well. Anthracene is supposed to be a very good scintillator, too; and Stilbene is commercially offered as a scintillator. The main concern I've had is whether or not this class of scintillator outputs light whose intensity is linearly proportional to the incident x-ray photon energy. Also the relatively-low x-ray "cross section" compared to the inorganic scintillators. Again looking at the NIST absorption edge data, carbon's "alpha" at 6Kev is 10.95, so to absorb 99% of those photons STILL will only require less than 5mm! This data is for pure carbon/graphite so polymers would have to be thicker than that. So I guess the main (remaining) issue is if any of these materials are proportional-enough to be useful in this particular application. It certainly is an intriguing idea to incorporate the light pipe AS the scintillator. You will have to keep us informed regarding your results <g>.
 
I am getting a PMT tube, maybe two. Also some avalanche diode SiPM(s) Also any low-cost scintillators that fit the PMT, so long as they are at least "new old stock". Also, any crystals I find interesting. Add to that any crazy plastic concoction I might stir up, with intentions of making a light pipe taper. Critical angle is close to that of glass near 42°

I have been cautioned by the lady of the household that any processes involving smelly stuff, fire with the risk of er.. "faster reactions", are relegated to outside, and must not scare any passing horses. (Just full of rules - this one)! Also, I have to collect toxic liquids. Cannot tip anything from methanol through paraffin all the way to toluene onto the road (as if I would ever do that)!
I mentioned I would be experimenting with "smoke alarms". Is that OK?

The "embodiments" are two. One kind just for development and messing with. Final electronics is small as possible, and uses a USB connection to a phone. Powered from the USB. The other side of the electronics has a multiple choice of photomultiplier technologies. You just leave out the unwanted components. It's a kit. If some HM members want to make up kits and move them to other HM members, that's OK. It would be cool if they do it at cost, and only cover their expenses. I have not thought through the probe part yet. It's size can be the same, whatever is inside. It has to fit the hand, seal up the light, house the radioactives.

I have not decided whether the computing should tax the processor of the smartphone, but I am inclined to having the computing done external, and the phone app is just a control and display device.

I am called away now. Playing with this gadget has to share time with certain other "household stuff", some of a relatively major nature. Nobody would begrudge me the construction of my shop outhouse/shed/man-cave/lathes repository/hideout, would they?
 
I found a web page describing experiments with a plastic scintillator coupled to a SiPM here . Unfortunately they didn't mention exactly which material they used. When they tried it with Americium they didn't detect any gammas at all. I don't know if that is due to their choice of scintillator or not...

And YES, there's nothing that should stand in the way of getting that man-cave built :grin:
 
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Check this out. Crystal thickness calculator that is based on the formula Homebrewed put forth:
formula_for_eff_cal.png


Efficiency calculator

The number of photons of a given energy stopped or "Percent Absorption" by a certain scintillator thickness is shown in the Efficiency Calculator tool.
www.crystals.saint-gobain.com www.crystals.saint-gobain.com

HB you are correct that the crystals can be very thin for the energies we are talking about. If you take 50 KeV as the max possible in our system:
For CsI at 50 KeV you only need .36mm to get 88% absorption. At 10 KeV only .03mm!
Interestingly, Plastic at 50 KeV requires 100mm.

Also useful to calculate shielding.

Robert
 
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Suppressing the phrase to begin with "in the light of the above", I try to discover what the scintillators actually do, and match it to the detectors we are considering. Thin or thick, that will be material dependent.
If I fumble here - then do help!

Some elements we might be interested in, that might be in an alloy, may be too low in response to be practical.
Like Boron, Carbon Nitrogen Magnesium. It would be nice if we could have got a response from carbon (0.277KeV), but that cannot realistically happen. The highlighted ones in the picture are the realistic range.

XRF Viable Elements.png

Silver steel will have Ag at 22eV and 24eV. The highest will be lead at 74eV and 84eV.
We gloss over some HM gun enthusiast possibly making bullets out of depleted Uranium.
I trawl the Epic-Crystal emporium looking for Eijen EJ xxx or Saint-Gobain equivalents.

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OK - so this one LYSO 30 x 30 x 0.5mm --> HERE for $90 should be suitable perhaps?
The range of main applications is not encouraging, but we now know some stuff.
It matches PMT tubes with bialkali photocathodes as well as SiPMs
It glows at 420nm, which looks like this colour --> #6a00ff RGB(106,0,255) ██████
The sensitivity is around 27600 to 33200 photons/MeV.
At best, 33photons/KeV
If 84KeV is is the maximum possible in our system, then that gives 2772 photons.
If that is the maximum, it comes to me across as possibly pretty feeble, but I don't know this stuff yet.

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.. or 20 x 13 x 0.75mm --> HERE#2 for £56 is maybe also OK?
It is also LYSO, as above, only a different size, and slightly thicker

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Among the plastics is the equivalent of --> Saint-Gobain BC 408 20 x 20 x 50 mm for $95.00
This one is 50% to 60% of Anthracene output, glows at this colour (#7600ed) or RGB(118,0,237) ▇▇▇▇▇
Almost the same colour output, fractionally deeper violet.
The blurb says "it is very sensitive for alpha, Beta-rays and other particles with lower energy range".
My mind says that may be OK for looking direct at Am241, but how good is it for X-Rays?
They don't say, so I go after anthracine. So far, I have not found what is 50% of anthracine's photons/MeV.

3 benzine rings. $35 for 25g from Aldrich - but we won't go there.
Apparently, you stir it into the acrylic and let it cool.
I think it is too short for a taper.
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Hmm - getting a scintillation to happen is one thing.
Having the sensor photocathode or diode be happy with it it is something else, and we need to pay attention to that.

Also, I want stuff that does not cost so much - unless there is no other realistic choice.
 

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keep in mind you will not get any X-rays above 59 KeV because that is the energy of the gamma from Am that is doing the excitation. It cannot displace a K shell electron of a higher energy. You will not see any characteristic x rays from Pb (K-alpha) because these are too high in energy.
I am not going to pretend I can be of help in selecting the scintillator. I know some of the Bruker units use NaI. I would consider CsI srongly since it is similar and not so hygroscopic.
Robert
 
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I would have checked on thorium from Coleman lamp mantles (older sort), but I think I will avoid them.
I have a couple of them, claimed to be good for checking Geiger counters.
Loose thorium dioxide is damn dangerous. Not very radioactive, but very bad if you get it on/in you.

Small X-ray tubes? I don't know.
Pretty much most other isotopes are not on. We can't be casually using cobalt gamma sources.

I read that common steels made from a proportion of recycled scrap have become more radioactive over the years, because of the crushed up radioactive junk that ends up in it. This includes scrapped hospital treatment isotopes.
I reckon if you test a steel with some of that in it, the detector will let you know pretty quickly.
 
@rwm : You mention not getting any X-rays above 59 KeV, because that is the energy of the gamma from Am241. We are now at the limit of my knowledge about how we work with wavelengths,

Does the 59KeV photon get weaker by inverse square law as it disperses in all directions (like light).
I get it that we are skirting around the "does it behave like a particle" thing, but I wanted to confirm that a 59KeV thing has a wavelength connected to that 59KeV by Planck'e constant, and that color of the photon stays that way.

This is where maybe @RJSakowski may know lots more than us. We talk of X-Rays, and gammas rays, but I am not sure where is the join. If I apply (say) 85kV to a electron tube, into a tungsten anode, is that a direct way of making a 85KeV photon, or do we only get X-Rays locked to the wavelengths the jangled up atoms of tungsten are willing to give?

Kα1 --> 59.32 KeV
Kβ1 --> 67.24 KeV
Lα1 --> 8.39 KeV
Lβ1 --> 9.67 KeV

These would be X-Rays, but with the sort of KeV we talk of when we mean "gamma", coming from Am241. I don't quite get that.

The actual amount of Am241 in a smoke detector is, I have read, about 0.1 milligrams. Is that right?

Still waiting the arrival of the PMT tube. Allegedly dispatched.
 
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