Alpha-particle spark detector

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Carl Willis
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Alpha-particle spark detector

Post by Carl Willis » Sun May 22, 2011 7:51 am

I recently completed a wire spark detector for alpha particles, following the technique of Tim Raney. Thanks to him for sharing many of his design notes and experiences. An early thread of his here on the forums mentions spark counters, but I think the details and wonderful results of his work are known only to those of us who have been privileged to observe them at Richard Hull's HEAS meetups.

viewtopic.php?f=13&t=5494#p33938

My interest in this simple open-air counter--a close relative of the Geiger "point counter"--was spurred recently by the need for additional hands-on activities for a program on lightning I presented for the local public television station. I put my device together from metal and plastic scraps on hand and a bit of tungsten wire from eBay. My audience yesterday seemed fascinated with it (and nobody got shocked). To appreciate these things, they really have to be experienced in person. The next best thing is a video (see the description for further details on construction and operation):

http://www.youtube.com/watch?v=-8GlzUjYazs

The attached photos show the vigorous reaction to 5-mCi Po-210 and ~10-uCi Ra-226 sources, respectively.

-Carl
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Scott Fusare
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Re: Alpha-particle spark detector

Post by Scott Fusare » Sun May 22, 2011 9:40 am

Great work Carl!

I have been enamored of this device since first seeing Tim's version many years ago. Out of curiosity, what did you use as a bias supply?

Scott

Edit: Sorry, I just realized the details are in the text accompanying the video.

richnormand
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Re: Alpha-particle spark detector

Post by richnormand » Sun May 22, 2011 3:35 pm

Very neat Carl.
I'll build one this afternoon. Just needed a good excuse to play with the metal lathe.
Can you detect cosmics with it too?

Jon Rosenstiel
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Re: Alpha-particle spark detector

Post by Jon Rosenstiel » Sun May 22, 2011 11:16 pm

Very well done, Carl. I've had Tim's spark counter on the back burner for quite some time... one of these days I'll have to spring into action and actually build one.

Jon R

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Richard Hull
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Re: Alpha-particle spark detector

Post by Richard Hull » Mon May 23, 2011 2:09 pm

Note to all as regards this device. You will need a fairly vigorous alpha source to really get good "play". I prefer grounding the wires as your hands may have to approach this area quite closely if you have a weak source.

Once a good source is in hand, you might invest in the time and effort to embed it in a nice insulated plastic rod or stick. Placing a 100 megohm resistor in series with the hot lead will reduce the danger along with spark brilliance and noise a bit, but a small coil around the ground lead hooked to a small radio shack battery powered speaker will make a great sounder.

I have wanted to "play" with closer spacing, (reduced voltage), flowing inert gas (argon), etc. I am almost on top of retirement and have these projects piling up

Lotsa' room for innovation and coolness here.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Larry Upjohn
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Re: Alpha-particle spark detector

Post by Larry Upjohn » Mon May 23, 2011 10:12 pm

Seems to me in past discussions here or elsewhere that an inexpensive bugzapper paddle was the source of a power supply for this type of spark detector. This would make it portable and fairly cheap. This technology seems to be replacing bubble detectors since signal extraction is easier to convert to digital format for counting and tracking through wire grids to determine particle direction, etc. My piece of trivia for the day. Larry Upjohn.
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George Schmermund
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Re: Alpha-particle spark detector

Post by George Schmermund » Mon May 23, 2011 11:23 pm

If your looking for an interesting source of somewhat fine wire for this type of experiment it would be worth checking out the eBay listings for acupuncture needles. The assortment is huge and some of the diameters get down to 0.16 mm. Not as fine as some of the W wire that's available, but they're very cool to play with as corona points and such.

Even the small gage ones are very stiff and springy. It goes without saying that the business end of the needle is extremely sharp. The ones with the coiled wire handles are so nice to work with that I consider them to be a sort of primary tool. If you do any microscopy, these needles are indispensable for poking around on a micro-sample. They're dirt cheap and should have a place on any science hacker's bench.
Anything obvious in high vacuum is probably wrong.

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Carl Willis
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Re: Alpha-particle spark detector

Post by Carl Willis » Thu May 26, 2011 5:17 pm

I've attached the original paper describing this kind of spark detector, from Physical Review in 1945.

To clarify my power supply, it's a 15-kV Plastic Capacitors, Inc. "brick" operated through a Variac, with the positive output grounded. I know Tim Raney has used rectified NSTs with success. The supply (and whatever load resistors are in use) needs to support a nontrivial amount of corona current, maybe 0.3 mA, even when the detector is not sparking. For this same reason, the shock obtainable by accidentally touching the cathode is more of a "biter" than your everyday static discharge and some attention to that is perhaps warranted. I think a electronic fly swatter power supply could drive this apparatus through a Cockroft-Walton circuit of a few stages substituted for the usual rectifier and storage cap. For what it's worth, such a fly swatter by itself can't be triggered by Po-210 alpha particles--I've tried that.

-Carl
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Doug Coulter
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Re: Alpha-particle spark detector

Post by Doug Coulter » Thu May 26, 2011 5:26 pm

What I'd love to see is someone building a real spark gap chamber with multiple plates and see it in action on cosmics.

One I saw at the New York world's fair in the '60's is what "sparked" my interest in this whole area in the first place, theirs was nearly a cubic meter in size and very impressive - a real crowd pleaser back when the idea of a few cosmics passing through you too didn't frighten everyone so much.

I've always wanted to build one myself, but it's hours in the day and money, and either that or fusors, so it hasn't happened yet. I've seen a few on the web, but darnit, I want one on my end table.
http://sciencedemonstrations.fas.harvar ... e=maximize

If you could use ITO coated glass for the plates so as to see through the entire thing....well, it probably wouldn't last too long, sigh.
Why guess when you can know? Measure!

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Re: Alpha-particle spark detector

Post by David D Speck MD » Thu May 26, 2011 6:32 pm

Doug,

I, too was fascinated by "The World's Largest Cosmic Ray Spark Chamber" in the exit rotunda of the GM Futurama pavilion at the 64-65 NYWF. I also want to build one, and have all the parts and a schematic, just need a couple of months with nothing else to do.

See the extensive posts on this display at:

http://www.worldsfaircommunity.org/topi ... ery-photos

My contributions to the chatter are on the second and third pages., I actually contacted the designer of this system a while back. Regrettably, it was only one of many that he built in his career, and he barely remembered it. All the details I have are in the linked post.

Dave Speck

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