Alpha-particle spark detector

[Carl Willis]

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

[Scott Fusare]

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]

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]

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

[Richard Hull]

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

[Larry Upjohn]

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.

[George Schmermund]

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.

[Carl Willis]

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

[Doug Coulter]

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.

[David D Speck MD]

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

[Doug Coulter]

Thanks for the link! I was checking to see if I was in any of those pix myself. At the time I was being allowed to do the presentation for Melpar's speech synthesizer/vocoder nearby so the booth babe could take a break (I was a kid then, but my Dad was the project manager, so they cut me some slack -- and I knew more than the babe anyway). Did you see the (Swiss? Nordic at any rate) electrostatic/HV displays too? They were killer-cool E-Motors and they ran them up to sparking to make them look cooler yet.

Yeah, I'm in about the same state, pile of parts and no spare time...rats. But I suppose we're getting a little off topic here, oops.

[Winston]

Unfortunately, the link to http://jamsci.org that was referenced in the older thread you linked to seems to be dead. Anyone have a copy of the the construction details, testing, diagram and references that were available at that site?

Carl Willis wrote:
> 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

[Joe Jarski]

I thought this was a cool piece for demonstrations when Carl originally posted it and finally got around to building my own.

Wire size and spacing is the same as what Carl used. I have 8 wires on mine and the HV supply (~5kV) is mounted in the box to the bottom of the FR4 and I use a wall wart for power.

[Carl Willis]

Hi Joe,

Nice craftsmanship. Is it working properly for you? One important trick is getting the right load resistance between the power supply and the spark detector. I use a 10M Caddock HV resistor for this function.

-Carl

[Joe Jarski]

Hi Carl,
Thanks for the compliment! It seems to work well. The sensitivity appears to be about the same as yours, as best as I can judge from your video. I'm using a 50M resistor that's similar to Caddock's. The sparks may be somewhat on the weak side - they're a little difficult to see in a sunlit room, but I'm happy with the way it works. Here's an action shot (I don't have the "super" alpha sources that you have)...

[Carl Willis]

Nice operation, Joe. Is your 5-kV supply a commercial item? I like the compactness you've managed to achieve and might like to make mine a bit smaller too.

-Carl

[Joe Jarski]

Carl, My HV supply is built on some generic boards that I had made. They use a CCFL inverter for the HV and can be stuffed for a one or two stage multiplier and either polarity. I keep several on hand and built them up as needed for GM tubes and neutron detectors. The 5kV is about the limit for these particular boards and inverter. I'm getting some others for another project that'll go up to 10kV.

This is what the inside looks like. The PS is kind of ugly because of the 50M resistor placement and the HV section having a coating slopped on it. I didn't intend to use these boards at 5kV so the big resistor is hooked in there kinda funny because of the size. If you want a PCB or bag of parts for the PS, let me know.

[Steven Sesselmann]

Joe,

Compliments, a very neat project...

Steven

[jcs78227]

Joe,

I have to echo some other's observations: you did an excellent job. If I didn't know better, I'd swear you bought it.

I've had a roll of tungsten wire sitting around since seeing Carl's build last year and still haven't put together the PS yet. For sure, it will look nowhere near as good as yours. That's slick!

-Jonathan

[Carl Willis]

Hi Joe,

I like your little board. It will fit conveniently in the plastic base of my detector, according to my best abilities to size it up in the photo. I'll contact you off-list about getting a parts kit. What's the circuit over to the right of the inverter? Is that an input voltage regulator?

Thanks,
Carl

[Joe Jarski]

Yes, the circuit on the right is an input regulator. It does a good job of regulating the output voltage for detector tubes where the voltage isn't real critical. I have a 12V PS that I use to run the HV boards on several detectors in the lab so I don't have to tie up my other HV supplies.

[Mark Rowley]

Hi everyone,
Its been awhile since I have posted here, but still lurking around every week or so. Several weeks ago I saw this thread and immediately realized that I had to build one. A Saturday afternoon produced this version which still seems to work remarkably well.

Thanks again Carl for the fun project.

http://www.youtube.com/watch?v=HO8VDf_r ... ideo_title

[scientificpages]

Hi! I found this thread once and i decided to make my own spark detector. Here is what i made:

http://www.youtube.com/watch?v=WCOmPcldqo4
http://www.youtube.com/watch?v=uic5sht2LEY
http://www.youtube.com/watch?v=k3E8bkKQbIs

[John Futter]

It is a pity your reading comprehension hasn't allowed you to post correctly on this site
moreover you freely admit to this site giving you the idea but then forget to give credit in your youtube postings.
There is nothing scientific in these acts
more plagairistic
move along

[Richard Hull]

I guess I don't see a major issue here. The original idea is credited in the first video as nothing new and a 1944 idea. Tim Rainey and I discussed it at a monthly HEAS meeting long ago. I had built one when in jr. high school (50's) and Tim built his model over 7 years ago. Carl saw Tim's, built one and posted it.

A number of these type systems were built, flown and photographed in 40's 50's and 60's balloon and aerobee rocket flights in cosmic ray studies.

I did find this video on you tube, and other than for the heavy breathing due to microphone gain, apparently the strings are activated by the violent expanding air molecules of the discharge to make them ring up. I am assuming that the magnetic pulse of the discharge is a bit weak to pluck the strings. A lot depends on how much energy is in the power supply's filter cap, if there is one.

http://www.youtube.com/watch?v=uic5sht2 ... ure=fvwrel

Richard Hull