Needing more than a spark test?

No to the bicycle pump. There are low cost pumps that will get down to around 50mm of Hg. Better yet, a compressor from a refrigeration unit will make a decent vacuum pump. I would prefer getting to 1 mm of Hg and then using the procedure that I described above. I use a 5 micron pump myself.
 
There are some really cheap photomultiplier tubes on eBay. How hard would it be to make the support electronics if you knew the specs from the manufacturer? BTW the one you posted earlier is now half price!
Robert
 
@rwm : Wow - Wow - WOW !
Who knew we had a HM member who can just point at his own X-Ray tube?
Then again - I am the nutball hoarding 2 electron beam guns!

More seriously - I am still thinking we can do better. I still don't quite get how the X-Axis is defined with EDX, unless it is something related to the higher energy (shorter wavelengths) taking longer to drop out of the excited state.
I see some plots where the different materials make a pulse in a definite new place, but I don't understand how EDX (energy dispersive x-ray) stretches out a spectrum.

The WDX way more immediately is understood.
Start with smoke detector sources.
Settle for a nice low cost photomultiplier tube.
A scintillation material - maybe ready attached, maybe separated, but coupled with lens oil.

Then a (something). A diffraction grating maybe? Mounted on the end of a shaft turned by a little stepper motor. It need be nothing more than one of those little things salvaged from an old floppy disc drive, or an adapted RC servo from the model plane flying fraternity. It rotates in steps, and aims the separated photons belonging to each material at the scintillator. A spectrum analyzer - except we don't have an array of photo-multipliers around it, so we rotate the grating instead.

This stuff must have been well researched already. Are we just scratching in the trails of already developed expensive machines?
 
RJSakowski said:
No to the bicycle pump. There are low cost pumps that will get down to around 50mm of Hg. Better yet, a compressor from a refrigeration unit will make a decent vacuum pump. I would prefer getting to 1 mm of Hg and then using the procedure that I described above. I use a 5 micron pump myself.
Click to expand...
I know that some of the newer diaphragm pumps can make a respectable, if not hard vacuum. 10E-2 to 10E-3 millibars. Going any further requires vane pumps stacked with oil diffusion pumps, or a turbo-molecular pump on the end of it.
So suppose I salvage a fridge compressor. How does it come to work "backwards"?

[Edit: There are some cultural downsides into simply typing "vacuum pump" into the eBay search box.]
 
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graham-xrf said:
I know that some of the newer diaphragm pumps can make a respectable, if not hard vacuum. 10E-2 to 10E-3 millibars. Going any further requires vane pumps stacked with oil diffusion pumps, or a turbo-molecular pump on the end of it.
So suppose I salvage a fridge compressor. How does it come to work "backwards"?

[Edit: There are some cultural downsides into simply typing "vacuum pump" into the eBay search box.]
Click to expand...
I am not aware of any diaphragm pumps that can get down to much less than 3-5" of Hg. 10E-2 mbar =7.5microns Hg which is getting into the range of rotary vane pumps.

The compressor is in a closed loop system. The function of compression side is to convert the gas back to a liquid but equally important is the suction side of the pump which lowers the pressure to cause the lowering of temperature as the refrigerant evaporates.

On an online search there are mixed messages as to the amount of vacuum a refrigeration compressor can pull ranging from 1mm to several inches of Hg so not as good as I had thought. In addition, small compressors typically require recirculation of the oil to keep them lubricated. It can be done but it adds to the complexity.Finally, responsible repurposing of a refrigeration compressor requires a provision for capturing the refrigerant. This can be done by a refrigeration repair shop or possibly, they have a compressor already pulled from a defunct unit they could give. Loss of refrigerant due to leaks is a common failure mode.

I noticed the "cultural downside" when I went to eBay UK. We tend to be a bit more prudish this side of the pond.
 
The xray tube is a cool decoration. It was given to me by a medical repair tech. Pain in the ass to get it out of the housing!
But I think I misunderstood your question about transparency. I now believe you meant to visible light not xray. Sorry.
I am having a hard time understanding how you plan to separate the energies. Is it a quantitative effect on the number of photons hitting the face of the PMT?
Robert
 
I am still trawling everything there is about material identification, learning about Raman handheld spectrometers, finding out about Compton scattering, and what is an Auger electron, and why that produces a special little piece of spectrum.

In the most practical way, I am still only seeking to winkle out some scheme to cook up a materials identification gadget, simple, and very cheap, and can be made by most HM members, perhaps with some help between them.

I was thinking shining an IR laser diode salvaged from outdated CD/DVD units, and using a $1 avalanche photo-diode from Mouser.com, or DigiKey might have possibilities, but I am not plugging for anything definite yet, until I know more of the physics, and what property we are trying to exploit.

If it has to be bombarding the steel with ex smoke detector radiation, then fine. Now what wavelengths come back, and how do we use them? If we use some other energy, IR, whatever, that is a new game.
- - - - - - - - - - - -
Re: The diaphragm vacuum pumps, I have actually used a dual-diaphragm type at a place I worked, but now I forget the brand name.

My usual fare was industrial sized tandem vane pumps, with very large diameter valve openings to oil diffusion pumps, or sometimes turbo-molecular pumps. With all the Edwards vacuum gauge kit, and pump-down sequence logic instrumentation, they come expensive! The change-over from hot-wire Pirani bridge gauges to Penning ion gauges comes at about 10E-3mbar, where there is not enough gas to keep the hot wire working. There was one type which could "bridge the gap", getting to part way to 10E-4mbar.

Then I found the small dual-diaphragm non-oil pump, and it really could make low-grade vacuum, certainly up to 10E-2mbar. If I find it again, I will post it.
 

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rwm said:
The xray tube is a cool decoration. It was given to me by a medical repair tech. Pain in the ass to get it out of the housing!
But I think I misunderstood your question about transparency. I now believe you meant to visible light not xray. Sorry.
I am having a hard time understanding how you plan to separate the energies. Is it a quantitative effect on the number of photons hitting the face of the PMT?
Robert
Click to expand...
Not at all. You did not misunderstand. For me, transparency is not restricted to visible wavelengths.
Also - I am not yet sold on any single method.

The type we are discussing is if you hit a material hard enough with radiant energy, you can get it to glow by florescence, and the color is characteristic. . This might be too feeble a glow to see - only a few photons. The radiant energy might be infra-red light, or visible light, or UV, or electrons (i.e.beta radiation), or even X-Rays.

The radiation from Americium 241 in quantities as small as 200 nanograms is not considered harmful unless you eat it, but can provoke glow photons from elements, and these can be detected. They also arrive over a time, and the characteristics are related to the elements - a signature. A built-up plot of many arriving to make a trace. It can take seconds or minutes to gather enough.

The "other" way is to have some gadget to disperse the response glows by color - for that read "wavelength". This is not as straightforward as prisms. Diffraction gratings made by capturing laser holographic interference onto photographic resist are unlikely to be an "easy thing".

There are characteristic responses that can identify materials from shining infra-red at them, A totally different method, but with maybe easier routes to a cheap DIY getup.

I do love your X-Ray tube!
 
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