Liquid Scintillation vs. Pancake GM

[Frank Sanns]

It may be better than you are giving credit Richard. To make a fair comparison, either price or detection area needs to be considered.

Using one of our large He3 dimensions of 22" x 1" that is a surface area of 2 x pi x r x h. Solving gives 69 square inches of surface area. This can be doubled with a little ingenuity in a liquid cell so both side of the silver/liquid scintillator emissions can be detected by a PMT. Silver can be rolled out into strips to construct such a cell and at $40 and ounce of silver that would allow for ten ounces of the metal to get to a discount price of an He3.

A cell with ten ounces of silver rolled out to 69 square inches should yield a hell of a cell with 138 square inches of effective detection area. Just sayin.

Frank Sanns

[George Schmermund]

Frank - Thanks for understanding what I'm trying to do here. For reference, let me say that this cell used 3 quarters. That represents less than 20 grams of silver content. The rolling stretched them out to ~1" wide and ~15" long. The three of them then make ~45 sq.". Therefore, ~90 sq." total for both sides. I used a hand corrugator to zig zag one of the foils to make the spacer for separating the spindled other foils. This controls the uniform spacing between each facing foil and adds to the amount of available silver for activation.

I appreciate your 3He tube analogue and the heroic amount of silver you compared it to, but 1 ounce of foil at 2 or 3 mils thickness would cram this small cell. That's not to say that a bigger cell with more silver in it wouldn't be a better detector, I just don't want people to assume that large quantities of silver are necessary for getting good results.

As far as Richard's assessment that this detector would only be of interest to newbs because a highly sensitive detector is of little value or interest to the real players here, well, what can I say?

[Frank Sanns]

Beta particles will only traverse the thinest of metal films so my guess is if you could get 0.005" to 0.015" silver foil you would be good to go. You might even be able to get away with using ammoniacal silver and a reducing sugar to plate out a thin film of silver out onto a plastic or glass structure.

Thanks for the work George. I will have to fire up my fusor soon and give this a whirl.

Frank Sanns

[Dan Tibbets]

Perhaps a stupid question, but isn't Borno10 an excellent neutron absorber? Wouldn't that decrease the aviable neutrons left for detection within the detector? How good of a neutron moderator is B10? I would not think it great based on it's atomic weight. Does this effect have benefits greater than the neutron absorbing properties that would allow for a net detection benefit? Are you considering some resonance peak for the silver?

Dan Tibbets

[Carl Willis]

Steven's idea, which is an entirely different animal from the thread's topic, is to detect the 478-keV gamma ray from the product of the first reaction below:

B-10(n,a)Li-7* (94%)
B-10(n,a)Li-7 (6%)

For examples of this gamma ray being detected see:
viewtopic.php?f=13&t=5478#p33922
viewtopic.php?f=13&t=5280#p33724

-Carl

[Brian_Gage]

Being new, I had a time deciphering the acronyms. Okay, PET is a polyethylene plastic, the container was 2 inches. Was that diameter? And how tall? Did you improvise with a recycled food or medicine container? What is the liquid inside this container? Why was the scintillation counter placed so much further away from the neutron source? I'd like to build a scintillation detector, maybe even a counter (with help since I can't see). Right now I've only got a Monitor 4 EC linked to my computer for small, rather tame experiments.
Appreciate any feedback on your post. Regards. Brian

[George Schmermund]

Brian - The container was from eBay: item #250810955009. I chose the ones with the white lids.

This is the LS cocktail that I used: http://www.mpbio.com/product_info.php?f ... y=01882470

The !5" distance was chosen because that was as close as the detector would fit. The next detector will hopefully fit on the oven platform where the GM/coin was tested.

A new and improved design is already in the works, but the basics are the same. I'll post some pix and new info soon.

[Richard Hester]

Interesting - using the liquid scintillator, you could count the proton recoil traces that happen in the process of moderation, and then verify your findings by looking at the activation induced by the moderated neutrons.

[George Schmermund]

Frank - Your idea of using Tollen's reagent / reducing sugar Is a good way to silver the inside of the cell. This would provide the inside surface with a highly reflective deposit and also add more Ag for activation. My next cell design incorporates the same idea, but I'll be coating the inside wall with evaporated Ag from a hot filament. I have this method ready at hand and it will require no wet chemistry except for the cleaning process to prep the cell for deposition. This method will also allow for considerable film thickness which is easy to monitor and control. The more silver the better. Your method is also excellent and within reach of those who don't have a vacuum deposition system available.

[Frank Sanns]

It wasn't liquid but back in the days when we were still looking at Hornyak buttons for neutron detection, I always wanted to make one with silver foil convoluted into the scintillator. Looks like you have taken it way beyond. Making me itch to get back to some of this stuff and stop putting out the fires that others light.

Frank Sanns

[George Schmermund]

Carl - I finally got around to doing an accurate measurement of the foil surface area. The weight was easily available from the mint website. But I guessed at the surface area since it wasn't simple to get a really good number from the foil because it ends up shaped kind of like a scimitar after extensive rolling. Today I rolled out more quarters to the same thickness, length, and width as the test samples. They come out remarkably similar each time.

Anyhow, I took a piece of 8.5" x 11" paper and used it as a template to cut a piece of aluminum foil. This makes it easy to get a good number for the weight of a sq." of Al foil. I then used an Exacto blade to trace the rolled out coin on another piece of Al foil. It works out to be 11.54 sq." of Ag foil for each face. That makes a little over 69 sq. " foil area in the cell that Jon R tested. This number is encouraging because it will be easy to put much more surface area into the same size cell by using squared up foil stock.

[Richard Hester]

Toluene is available in gallon lots at the Evil Orange and other hardware stores. A few grams of fluorescent materials transforms it into a scintillation cocktail, though some treatment (bubbling through nitrogen to get rid of fluorescence-quenching dissolved oxygen) may help to optimize things. Though the toluene is not near as dense as polyethylene or polypropylene, it will moderate fast neutrons. The process of moderation generates recoil protons that can be detected by a PMT from the havoc they induce in the scintillator. The point is one could use this as a moderator for a silver foil, count the prompt recoil proton reactions, then turn right around and count the delayed silver activity with the same solution and PMT.

[Richard Hester]

It's amazing what you can find if you nose around a bit using Google - in this case a citation regarding a less expensive/toxic/flammable/volatile liquid scintillator cocktail based on medicinal paraffin (mineral oil to U.S. readers - the scientists were Brits...). It's about 1/3 as sensitive as a standard liquid scintillator, but not flammable/volatile. It doesn't suck a lot of expensive fluors, either The mixture consists of mineral oil with 0.8 g/liter p-terphenyl and 0.008 g/liter POPOP. The purified oil from the drug store works better than the industrial variety. As a comparison, one of the sources I saw was talking about 100g/liter of PPO in toluene - that's a lot of money!

Another citation mentiions a mixture of 3g/liter PPO and and 0.02g/liter POPOP in mineral oil. This particular mixture has 28% of the activity of a toluene solution, but perks up to 67% if one adds 90g/liter of naphthalene.

Both of these mixtures look like attractive candidates for a combination moderator/scintillator, both for simple activation experiments and a combination of recoil proton/activation measurements. The lack of volatility and compatibility with plastics like perspex/lucite is a plus.

[Richard Hester]

Another interesting twist in the standard detector might be to use the mineral oit scintillator as a moderator for one of those Russian corona tubes, monitoring the scintillator with a PMT the same time. That way you get prompt readings from the fast neutrons via recoil and the same neutrons moderated via the corona tube.

[Dustin]

This is very interesting, thanks George.
Perhaps silver wire wound on a frame would increase surface area
or treating the foils with sandpaper.
Maybe even silver plated coiled "flywire mesh".
Some good coax has silver plated braid that would have a huge surface area. Carefully removing it, you could fill your container with tubes of braid.
Steve