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Author: Subject: Not just another ZnS question.
nitroboy
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[*] posted on 17-9-2004 at 03:06
Not just another ZnS question.


I figure burning Zn and S liek a flashpowder will give ZnS.
I'm using the ZnS as the screen for my electron gun, and i was wondering if deflagration products here would be pure enough.
And would permeating a solution of ZnS onto paper be sufficient for use in my screen?
In theory with my AC current i should get a lovely sinusoidal pattern on the screen from the electrons.
any thoughts or comments?
the gun is complete and all that is lacking is the screen.
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vulture
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[*] posted on 17-9-2004 at 03:40


Zn + S ----> ZnS

But, since the reaction is highly exothermical:

2ZnS + 3O<sub>2</sub> -----> 2ZnO + 2SO<sub>2</sub>




One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Marvin
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[*] posted on 17-9-2004 at 09:00


There is good information on the FTP. Essentially you need ZnS as a fine insoluable powder, it also needs a dopent, copper, manganese, silver, etc.

The powder needs to be cooked at a high temp for an hour or so to turn the usual form, cubic, into wurtzite (I think I have this the right way round). Its rather sensitive to processing as light is emtted from damaged areas of the wurtzite lattice.

Simply burning Zn and S together probably wont work well. ZnS has rather a long decay time for a phosphor, any reason you want this one?

There is also a description of a phosphor for a home electron tube, based I think on a silicate. Either way, you seem to need a furnace. You would probably be better buying some doped zinc sulphide, I used a commercial glow in the dark paint powder to make a spintharoscope, it worked rather well.
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[*] posted on 16-11-2004 at 16:11


Can someone tell me where on the FTP to look for this information? I would like to use zinc sulfide to detect low energy (around 10kv) X-rays.

Also, I am curious if anyone here has done any experiments with scintillation (either with homemade ZnS or "glow in the dark" powders), using a weak source of radioactivity such as a uranium rock, "anti-static" brushes, or the Americium in a smoke detector.
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neutrino
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[*] posted on 16-11-2004 at 18:46


I have played with one of United Nuclear's visual counters for a-particles with a standard smoke detector source and it worked quite well. They use doped, cooked, etc. (some more info on their site) ZnS for these things.
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a_bab
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[*] posted on 17-11-2004 at 02:17


I upped the info some time ago about zinc sulphide phosphorescent powder. There is info about "phosphor" powder aswell in that file.
There is another doc (could be an image) upped by somebody else. Just look for "zinc" in the filename.
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[*] posted on 18-11-2004 at 15:32


Thanks. Informative article. I see it is not at all that trivial to "activate" zinc sulfide.
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[*] posted on 11-12-2004 at 17:15


I had a modest amount of success making glowing sulfides. I ignited Zn powder + S powder, with various added impurities. I made about a gram each time. For the impurities, I tried small amounts (< 10%) of copper sulfate, copper powder, sodium chloride, and silver nitrate. I also tried "cooking" the resulting powder for several minutes with a torch and up to an hour in direct contact with a red-hot stove burner.

I had the best results with sodium chloride as the impurity, and the worst results with the copper impurities. "Cooking" afterwords did not seem to have much effect (maybe was not hot/long enough).

The resulting powders would glow for about 15 seconds when charged with an ultraviolet ("black";) light. In total darkness with eyes adjusted I had no trouble seeing the glow. Using a flashlight instead of an UV light, though, the glow was extremely weak and the only way I could see anything is if I closed my eyes while the flashlight was on and opened them as soon as I turned it off. Certainly though the glow was far less bright and lasted a much shorter time period than commercial glow products.

All the glows looked yellow-green to me - even the silver which I though was supposed to be sort of blue.

This is an interesting experiment and not that difficult to do. The product is not likely to be of much practical use when prepared the way I did it though.
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[*] posted on 2-2-2007 at 17:57


Actually, I believe that your product would be very useful as a scintillator, as they require chemicals that do not fluoresce very much unless they are stimulated with ionizing radiation.

- EDIT -

You need ZnS:Ag,Cu for the blue glow. ZnS:Ag is still greenish in color, although it has a noticeable blue tint.

[Edited on 2/3/07 by olmpiad]




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Ozone
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[*] posted on 2-2-2007 at 18:49


For liquid scintillation I recommend the use of the POP-POPOP fluor in toluene. Be aware that colored materials, viz. tar, asphalt, etc. will quench the scintillation by absorbing the light before it leaves the matrix (color quenching)-and- chlorinated solvents (amoung others, CCl4, etc.) will quench by absorbing the energy from the excited toluene before it is transferred to the fluor.

High efficiency scintillation crystals are NaI or CsI (hence the action of NaCl) doped with Thallium Iodide.

Barring this, there is some neat stuff called scintillation plastic that is used in some modern (lower cost) instruments. It is wild under LWUV and can be had (when last I checked) on a certain popular online auction site at reasonable cost. I would use this stuff--its tough, you can shape it, it's non-toxic, and is not hygroscopic. The lower density will result in lower counting efficiency, however.

For higher quantum yields (and longer triplet intersystem-cross/relaxation times), I'd go with Strontium Aluminate, which usually doped with Europium (which is used in many glow-in-the-dark applications, including toys).

See also plastic impregnated with ZnS:

http://www.blacklite.com/Products/Phosphorescent_Products.ht...

As for color (determined by dopant) in ZnS phosphors (I hate to do this, but I am lazy) a blurb from Wikipedia:
Zinc sulfide, with addition of few ppm of suitable activator, is used as phosphor in many applications, from cathode ray tubes through x-ray screens to glow-in-the-dark products. When silver is used as activator, the resulting color is bright blue, with maximum at 450 nm. Manganese yields a Orange Red color at around 590 nm. Copper provides long glow time and the familiar glow-in-the-dark greenish color. Copper doped zinc sulfide (ZnS:Cu) is used also in electroluminescent panels.

Coincidentally, ZnS doped with Eu (which supposedly boasts a much longer phosphorescent persistence) is for sale at United Nuclear (just for reference).

And finally, for reference, a very nice page on Antoine Henri Becquerel describing, among ther things, the use of ZnS screens... I love the scientific historians at lemoyne! This is a good historical reference somplete with citations.

http://web.lemoyne.edu/~giunta/EA/BECQUERELann.HTML

Best of luck with your tube,

O3




-Anyone who never made a mistake never tried anything new.
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olmpiad
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[*] posted on 2-2-2007 at 21:37


As for scintillation plastics, just frost the surface of plexiglass with some sandpaper, it works great!



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