A couple of days ago, I tried to use some of the Bicron ZnS:Ag phosphor I had bought from Richard Hull (thanks!) to make some fluorescent screens to view charged particles. Since my ultimate goal is to have a screen in a vacuum environment for detecting protons, I used Vacseal as a binding agent. Vacseal is a silicone-based liquid vacuum sealant good down to UHV, and no doubt has saved the rump roast of many a researcher. I used the Vacseal to coat microscope slides (cleaned first with Alconox, then with isopropanol). First thing - though the specs say that Vacseal takes a few days to cure at room temperature, it actually dries to the touch in a minute or two in a thin layer. I also had a little trouble applying an even coat of phosphor by sprinkling it on using a spatula. Result - three motley-looking fluorescent screens.
Last night I got a chance to try one of the screens out using a 25mR hunk of uranium ore as a radiation source and an 8X loupe as a magnifier. After a few minutes in the dark to adapt my eyes, I was seeing nothing but phosphenes. After a while of this, i got frustrated and took a look at the setup with a blue LED flashlight I was using to find my way around. The blue light caused a faint orange phosphorescence in the phosphor that persisted for a few minutes. I again tried to look for scintillations and found a lot of them. I replaced the uranium ore with a 1500 CPM radium check source and again observed scintillations, albeit fewer. I now need to find out whether my eyes finally adapted to the dark, or whether the blue light somehow activated the phosphor. I will repeat the experiment tonight with another screen.
Spinthariscope Blues, Pt. 1
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Richard Hull
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Re: Spinthariscope Blues, Pt. 1
The spinthariscope responds mainly to the heavy alpha particles only for human optical purposes. (there ain't a whole lot of energy in a scintillation) Betas and gammas don't cut it. So when making a spin-scope up, do not cover the rad material with anything thicker that a few angstroms!!! This way the Alphas will have range enough to blast the nearby screen. Likewise, the screen binder material must not bury the phosphors either or the alphas won't reach them to scintillate.
Screen to source distances need to be less than a CM for prime results. This means a large aperture eyepiece lens with good eye relief of at least 10X magnification.
The process becomes a real study in mounting two materials where the exposed surfaces are truly exposed and not covered by binder.
I have found it best to just spray a surface with an fine, "lay flat" adhesive and then "salt shaker" the phosphor onto the surface, tap and jiggle about a bit and them tap off the excess following a drying period. The excess is caught (as it is very expensive) and returned to the shaker device for reuse. You can make a ton of screens with very little phosphor in this manner.
I have a friend who uses double sided carpet tape and grinds the phosphor into one side of the tape, again, catching the excess for reuse. The other sticky side is used for mounting the screen.
The alpha emitter should usually be left in situ or mounted as found in some manner which will not spread it about in your environment. Again, the important point is to not cover the emissive material with more than a few microns of anything!
ALL BLUE AND MOST ALL WHITE LEDS EMIT IN THE ULTRAVIOLET!!
While not efficient in any way, they do cause phosphors to activate and some will stay active for hours after getting hit with the UV. Another bummer is standard fluorescent lighting! It will activate the hell out of the Bicron stuff which is just itchin' to scintillate. All this, inspite of Bicron's specs of sub microsecond rise and fall times on the phosphor. This may be a function of large mass excitation as by quadrillions of photos versus single site activation differential by only a few random alpha events.
FYI
Our own group's Tim Raney has successfully made screens in his vacuum tubes out of the Bicron stuff for electron bombardment. He uses SPIT to bind his phosphors. I find it hard to believe, but it seems to work. Don't think this is a recommendation. He may have had a nice meal of fatback prior to his application. You never know what the binder in spit is.........too variable. I only mention this as there are many ways to skin a cat.
Richard Hull
Screen to source distances need to be less than a CM for prime results. This means a large aperture eyepiece lens with good eye relief of at least 10X magnification.
The process becomes a real study in mounting two materials where the exposed surfaces are truly exposed and not covered by binder.
I have found it best to just spray a surface with an fine, "lay flat" adhesive and then "salt shaker" the phosphor onto the surface, tap and jiggle about a bit and them tap off the excess following a drying period. The excess is caught (as it is very expensive) and returned to the shaker device for reuse. You can make a ton of screens with very little phosphor in this manner.
I have a friend who uses double sided carpet tape and grinds the phosphor into one side of the tape, again, catching the excess for reuse. The other sticky side is used for mounting the screen.
The alpha emitter should usually be left in situ or mounted as found in some manner which will not spread it about in your environment. Again, the important point is to not cover the emissive material with more than a few microns of anything!
ALL BLUE AND MOST ALL WHITE LEDS EMIT IN THE ULTRAVIOLET!!
While not efficient in any way, they do cause phosphors to activate and some will stay active for hours after getting hit with the UV. Another bummer is standard fluorescent lighting! It will activate the hell out of the Bicron stuff which is just itchin' to scintillate. All this, inspite of Bicron's specs of sub microsecond rise and fall times on the phosphor. This may be a function of large mass excitation as by quadrillions of photos versus single site activation differential by only a few random alpha events.
FYI
Our own group's Tim Raney has successfully made screens in his vacuum tubes out of the Bicron stuff for electron bombardment. He uses SPIT to bind his phosphors. I find it hard to believe, but it seems to work. Don't think this is a recommendation. He may have had a nice meal of fatback prior to his application. You never know what the binder in spit is.........too variable. I only mention this as there are many ways to skin a cat.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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guest
Re: Spinthariscope Blues, Pt. 1
Last night I was able to consistently observe scintillations in two of my makeshift screens with both a piece of hot (25mR) uranium ore and with a radium check source. In each case, the screen was placed directly on top of the source, coated side down. Sucessfully observing scintillations was mainly a question of waiting a sufficient amount of time to adapt one's eyes to the dark. The screens look pretty awful, but they prove that Vacseal is a compatible binder for the phosphor. I plan to try some cheesecloth or silk screening cloth as a "shaker" to distribute the phosphor more evenly next time around. Also. it sounds like a good idea to find an appropriate solvent to thin down the Vaseal a little and increase its drying time. Vacseal also comes in a spray can. In retrospect, this probably would have been a better choice for evenly and quicly coating substrates.
Once I get an evenly coated screen, I expect that a photomultiplier will really go to town with the scintillations....
Once I get an evenly coated screen, I expect that a photomultiplier will really go to town with the scintillations....
Re: Spinthariscope Blues, Pt. 1
An easy way to make a fairly even screen is to make an alcohol slurry of the phosphor - about 30 mL of isopropyl alcohol works nicely. Swirl the mixture around to suspend the phosphor and gently pour out onto the screen substrate - glass would be good here.
Be sure to clean the glass with a good detergent and distilled (de-ionized ) water followed by an alcohol rinse and air dry.
To make a nice round screen, use an appropriate sized O ring, held down with a very light coating of silicone grease (on the outside of the ring, of course).
Let the alcohol evaporate and you should nave a nice evenly deposited screen.
Dave Cooper
Be sure to clean the glass with a good detergent and distilled (de-ionized ) water followed by an alcohol rinse and air dry.
To make a nice round screen, use an appropriate sized O ring, held down with a very light coating of silicone grease (on the outside of the ring, of course).
Let the alcohol evaporate and you should nave a nice evenly deposited screen.
Dave Cooper
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guest
Re: Spinthariscope Blues, Pt. 1
Hi guys, What kind of results could I expect out of straight ZnS?. I expect the persistence would be pretty long but I found a source for about $1 a gram, at that price I can experiment with different assemblies.