hodges
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Spinthariscope
I have some glow-in-the-dark paint and decided to try to make a spinthariscope. I painted some of the paint onto a notecard and allowed it to dry.
After confirming that this glows fairly brightly in the dark once charged by room light, I left it in the dark for several hours.
After allowing my eyes several minutes to get adjusted to the dark, I could still see just a slight glow from the card. I took an alpha source from a
smoke detector and held it close to the card. The result - nothing! Even looking at the card with a magnifying glass I could not see a thing.
I know my alpha source is good because holding it next to a geiger counter changes the slow ticking to a loud buzz. So what is the deal here? I take
it that zinc sulfide that can be charged with room light cannot be charged using alpha particles? It takes a different formulation? It seems to me
from reading an explanation of how zinc sulfide glow powders work that even if the alpha radiation was not right for charging the paint to glow
afterwards, it should still flash momentarily when hit by alpha particles. Is this not correct?
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Marvin
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Ive done this successfully. I added enough water to the paint to get rid of everything except the zinc sulphide and seperated it out. Anything that
blocks the alphas will cause problems and the paint I had was only about 1/10th ZnS. I then squashed the powder onto a rigid plate and held the
source (0.9uCi) about 2-3mm away. I needed a good magnifier to see the flashes. A microscope didnt help as it didnt have the field of view to catch
flashes very often.
Some notes. I left the powder in the dark for well over a day, when I did the experiment is was barely visible. I stayed in the dark for well over
an hour to dark adapt my eyes. A few mins certainly wont do it. Glow in the dark paint ZnS wont produce as bright flashes as the proper stuff, after
all its designed to spread the energy out, you do get flashes though instead of long term activiation.
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hodges
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Its surprising that the flashes were so hard to see. I would have suspected based on the counts I get from a geiger counter that the powder would
sparkle like mad. Certainly if it sparkled once for every count I got... but maybe that's unrealistic. Maybe powder designed to glow in the
dark is only a fraction as efficient as powder optimized for detecting alpha particles?
Assuming I used the correct ZnS powder (specifically manufactured to detect alpha particles), can someone tell me how much activity a 0.9 uCi alpha
emitter should produce? How much radiation would I need to produce a continuous glow of moderate strength? I know they used to make radium wrist
watches that glowed continuously - how much alpha radiation was in them?
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motman
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look here
http://tesladownunder.iinet.net.au/Nuclear,%20X-ray.htm#Spin...
and here
http://forum.4hv.org/index.php?board=4;action=display;thread...
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If_6_was_9
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Check out the zinc sulfide here http://www.unitednuclear.com/chem.htm
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David Marx
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Are you sure your paint contains zinc sulfide? It may be an organic charge transfer system and not zinc sulfide at all.
alea iacta est
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Marvin
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If it charges up in the light it cant be organic based. Newer paints use unsuitable silicates/aluminates so this is a good point, it needs to be ZnS
based. The flashes are very faint though.
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hodges
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This paint was definitely ZnS based given that it only holds a glow for an hour or two maximum after being charged up. I'm surprised the glow
would be so weak. Obviously different doping is required for optimal response to alpha particles. I recently even tried one of those staticmaster
cartridges (which sends my geiger counter off scale) and still didn't see anything.
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MadHatter
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ZnS
You may need a purer ZnS. United Nuclear - once a ripoff, always a ripoff ! If you have access to Zn and S powders, mix it up, light it up and test
what's left ! If possible, burn it in a can or any other
environment that deprives it of oxygen so you don't end up with zinc oxide.
[Edited on 12-12-2004 by MadHatter]
From opening of NCIS New Orleans - It goes a BOOM ! BOOM ! BOOM ! MUHAHAHAHAHAHAHA !
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unionised
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That reaction is great fun, but I doubt it will give better results than the commercial product.
A lot of the problem here is that luminous paint is meant to glow for hours and nuclear scintilators usually have emision lifetimes of nanoseconds or
micoseconds.
The alpha particle hits the ZnS crystal and transfers the energy. In one case that is released over a couple of hours, in the other, over a few
microseconds. Guess which one is easier to see.
You might do better with the phosphors used in lamps and CRTs, they have lifetimes comparable with the eye's response time.
Note that some of the phosphors in lamps, particularly old ones, are rather nasty.
[Edited on 12-12-2004 by unionised]
[Edited on 12-12-2004 by unionised]
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hodges
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I bought some commercial ZnS powder designed for detecting alpha particles. It glows light blue, about the color of a B&W television screen.
Results were ok but nothing super impressive. With a 500uCi alpha source, I had no problem detecting the glow in moderate darkness. It was not as
bright as "glow in the dark" powders, but the glow was clearly visible. Moving the source and watching the effect on the detector, one
would almost swear that there was a tiny light source that was just shining on the detector. It is kind of like when you use one of those infrared
detector cards to detect the beam from an infrared remote control. Seeing the beam shine on the card, you would swear that if you looked at the
infrared beam itself it must be shining visible light.
Using a 0.9uCi source (from a smoke detector), I was just barely able to see a slight glow holding the detector a couple milimeters away from the
source. It required a long period of dark adaptation to see anything with this source.
I was never able to see individual flashes. I tried using a magnifying glass and holding the source far enough away that the glow was barely visible,
and then moving the source slightly while viewing through a magnifying glass. I either saw a faint glow or nothing depending on position but never
individual flashes. Perhaps the room was not dark enough.
Contrary to popular belief, I did find that my ZnS also glows in the dark upon being charged with ultraviolet light. However, the glow decays to
nothing in a couple seconds.
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Marvin
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Excellent. May I ask where you got the phosphor from? I know a few people after the blue, including myself.
The ZnS:Ag blue is the best for electronic applications as it matches photomultipliers well (400-440nm peak). The eye is not very sensitive to blue
though and we dont focus it well on its own, I suspect this may be the problem.
You may have noticed that in low light your eye tends to lose the ability to tell colours apart. This owes to the cone cells in the eye not working
in low light. If you used green which the rod cells we use in low light are very sensitive to, you should see individual flashes easily when the
magnifier is in focus. I think this is ZnS:Cu but it may be ZnS:Mn, they are green and yellow from memory.
Its this effect that makes a green laser pointer at 532nm look some 30 times brighter than a 675nm Red one even though its outputting the same power
into the beam. I'm sure there is a similar effect of green versus blue.
On the subject of blue, aparently when people are 'flying' on stage with wires the wire itself (allready quite hard to see) is often shone
with a deep blue light to make it harder to focus on. Presumably a blue background is also used and the effect keeps the wire blurred. Why deep blue
is special wasn't explained.
You also may find that the area directly where you are looking, and the area you read with is less sensitive to light than a little to the side of
your center of vision. Presumably this is an effect resulting from looking directly at bright lights.
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hodges
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The phosphor is available from at least two sources. United Nuclear at $20 for 5 grams. Then there's a store on E-Bay that charges $20 but you
get 10 grams. The sad thing is - I bet either amount didn't cost 20 cents to make. But without access to a furnace and the exact formulation,
not much choice but to pay.
I did try some of my homemade ZnS with the 500uCi source and didn't see any glow. A "thermite" - type reaction with zinc and sulfur
does produce a powder that has some sensitive areas in it. These appear lighter than the rest of the gray powder, and they glow quite visibly for a
minute or more but only when charged with ultraviolet light. Regular light or alpha radiation do not seem to work.
My guess is that the "thermite" reaction could be perfected enough to make a usable product that could be charged with ultraviolet light,
although once done for the exprimental aspect of it buying commercial glow powders becomes cheaper just like with many other chemicals (the ones you
can get anway) are cheaper to buy than to make. If one could perfect a home reaction to make the alpha particle sensing powder I'm sure they
could make money selling it on E-Bay given the going rate of $2-$4 per gram though.
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Matsumoto_Hideki
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How about using paranapthalene?
i am not sure about this but I have heard that Anthracene or also known as paranapthlene works very well as a scintillator.
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Marvin
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The united nuclear phosphor is not what I need unfortunatly. I suspect the copper is included to make it brighter to the human eye.
Anthracene is the best organic scintillator, its not neerly as bright as the ZnS series though. If I could get that here I'd be trying it
anyway. For detection typically ZnS is used for alphas, anthracene is used for beta detection, and something very dense like BGO is used for gamma.
[Edited on 29-12-2004 by Marvin]
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Matsumoto_Hideki
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ahhh.
Ok I didn't know that.
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Texium
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Thread Moved
19-11-2023 at 10:18 |
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