Gadolinium Loaded Scintiilaors for Neutron Detection

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Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

...........Originally posted by Richard Hester who used (guest) back in 2001 on the old intranets board........
I have just run across a fascinating article on the use of gadolinium loaded plastics for neutron detection. Gadolinium has the higest cross section for thermal neutron absorbtion of any known element, so a scintillator loaded with gadolinium is "black" to thermal neutrons. The experimenters used gadolinium loaded polystyrene, vinyl polystyrene, or silicone with a gadolinium compound and PPO. The silicone used in the experiments was one with vinyl sidegroups to enhance energy transfer to the PPO. Sylgard 184 from Dow Corning is a 2-part silicone compound that matches this description.
A cylinder of scintillator with a modest cladding of polyethylene or paraffin coupled to a PMT would be a dandy neutron detector and might beat the pants off the usual BF3 or He3 neutron detector due to the enhanced neutron opacity of the scintilator. Apparently the neutron capture signature of gadolinium is easy to detect and separate from the usual gamma signature. If the scintilator is large enough, no moderator is needed, as it will act as its own moderator. More on this later...
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

Hi Richard, that sounds very interesting, is there any info on the net at all?.

regards
Mark Harriss
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

Try http:// www.y12.doe.gov/orsens/pubs/ydw-1824.pdf for the original article on Gd/plastic scintillators. The authors were a bit coy about the actual Gd carrier compound that they used. I am considering either gadolinium acetylacetonate or gadolinium octanoate.
DaveC
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by DaveC »

Richard - were able to tell if the Gadolinium is chemically combined with the polymer or just dispersed in it? Also.. isn't PPO, poly phenyline oxide, which is a bit different from poly-dimethyl-siloxane.. aka silicone?? No chemist, here....

Dave Cooper
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

The Gadolinium is in a separate compound dissolved or dispersed in the monomer of the plastic in question, so that it is evenly distributed when the monomer is polymerized into a solid mass. PPO is not polyphenylene oxide, but a fluorescent organic compound used commonly in scintillators. If you want to find out more about it, load up Google with the search parameters "PPO" and "scintillator". While you're at it, try the same thing for p-terphenyl and POPOP.
I am thinking more seriously about using Gadolinium Octanoate rather than Gadolinium Acetylacetonate as the Godolinium carrier, as the octanoate is a hydrophobic group and will probably dissolve more readily in the silicone monomer.The Gadolinium Acetylacetonate is available only as a hydrate, so I will have to get rid of the water by vacuum drying the compound before I even think of using it in the scintillator. As of yet I haven't had the time to call up my nearest chemical supply house to get pricing. I did find a place in Texas that will sell 1.1 pound kits of Dow Corning Sylgard 184, which I plan to use in the scintillator and also as a index matcher/glue for attaching scintillators to PMTs. The rub is that these folks have a $150 minimum order. Four kits will make the nut. With shipping and handling, the whole thing comes to about $170. They also take credit cards...
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by DaveC »

Richard -

Just a detail - PPO IS the standard designation for poly-phenyline oxide. It is sometimes referred to by the other names as indicated in the articles you referenced. The POPOP compounds are forms of phospine oxides.

Dave Cooper
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

It wouldn't be the firt time acronyms meant different things in different contexts( PPO means yet another thing in the health care context). However, when talking about scintillators, PPO is invariably 2,5 diphenyl oxazole and POPOP
is 1,4-Bis-(5-phenyloxazol-2-yl)-benzene. These two chemicals, along with p-terphenyl, are three of the most common fluors used in plastic and liquid scintillators.
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by guest »

It turns out that the reason that the authors of the paper on Gd loaded plastic scintillators (cited earlier) are coy about the Gd carrier they use is that they're patenting their particular process...
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Re: Gadolinium Loaded Scintilaors for Neutron Detection

Post by guest »

I just got to your December post on gadolinium loaded schintilators. If you guys decide to actually buy this stuff.. please post the cost. Just got my pmt bought. The consortium needs a fusorstuff.com website for all these neat items.

Larry Leins
Physics Teacher
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Rats!)

Post by guest »

I've taken a bit of time this vacation to look for the makings for a Gadolinium-loaded scintillator. It looks like I'll be able to buy POPOP (fluorescent wavelength shifter) through my local scientific supply house, but the only source I've found so far for Gadolinium compounds other than simple chlorides, oxides, etc., is Aldrich, and they won't sell to the supply house I'm dealing with. It looks like I need to do some more scouting around or cultivate an institutional connection. Ideally, we need a Gadolinium compound that will dissolve in uncatalyzed silicone resin, rather than just going into suspension. This is to avoid the cloudiness problems encountered in devices like ZnS-loaded scintillators. Some researchers use complex Gadolinium chelates not available from the usual supply houses. The closest I have been able to come so far is Gadolinium octanoate, which is a fatty acid salt of Gadolinium. Being hydrophobic, this stands a fair chance of disolving in the silicone resin. I won't know until I get some, though...
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Rats!)

Post by guest »

Richard-

Disclaimer:
For consideration only. In no way is it reccomended or advised for chemical procedures to be performed by untrained individuals and/or in other than strictly controlled laboratory environments. Safety is of paramount improtance.

For MSDS of GdCl3, see:
http://espi-metals.com/msds's/gadoliniumchloride.pdf

Exchange of the chloride for octanoate (or other long chain anion) would seem straight forward from GdCl3 using octanoic or decanoic or other readily available long chain acid.

This is related to the reaction that makes bath tub rings- potassium and sodium laurate (and other long chain acid salts) are soluble. However, Ca++ and Mg++ (and Fe+++, etc) in harder water can exchange for the Na+ or K+. These long chain salts of divalent and trivalent cations are less soluble and precipitate out from the water (dragging body oils with them) creating the nuisancesome "soapscum". Though GdCl3 is soluble in water, its long chain acid salts may well not be (especially at sub ambient temperature).

With this in mind, perhaps the acid could be a functionalized silicone oligomer:
http://www.gelest.com/productline/ReactTable.asp

And it looks like the professionals have already patented this approach:
http://www.y12.doe.gov/orsens/neutron.htm

Perhaps one could obtain a sample from them?

R
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Rats!)

Post by guest »

Doing what you say -combining a Gd ion with a medium weight fatty acid - is straightforward in theory. The devil is in the details. You want to use a medium weight hydrophobic group so that you don't dilute the concentration of Gadolinium too much. The rub is that all the medium weight fatty acids stink. Horribly. With a capital "S". Octanoic acid is otherwise known as caprylic acid, and it smells like a herd of rutting billy goats. One drop on your skin will turn you into Mr. Popularity for quite a few days. Synthesizing and purifying the octanote will involve a lot of work with messy and/or dangerous solvents I wouldn't want to have around the house. Just the smell would be good for a divorce or an eviction.

The last URL you reference is the publicity paper for the silicone scintillators developed at Oak Ridge. The URL for the actual research paper is listed in a earlier message in this thread. The Oak Ridge guys are using an unspecified Gd carrier. The silicone is only a matrix and excitation source for the PPO phosphor that does the actual scintillation. Some Russian researchers have also used a complex Gadolinium chelate to load a solid scintillator.
I haven't given up looking for a suitable (pre-made) Gd carrier yet, it's just that the easy source (local science supply shop) won't work for the Octanoate. I have a couple of other tricks up my sleeve, one which might allow me to use gadolinium oxide. Meanwhile, my plate is full with 3-4 other types of neutron detectors and associated electronics. I also just ran across a batch of PIPS detectors (rugged silicon charged particle detectors), and I will be adapting the circuitry I have developed for the plastic scintillators for use with a Silicon detector. As with all the fusor stuff, I work on each piece as it becomes available. This one is going to take a while.
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by guest »

I read the Oak Ridge Gadolinium scintillator paper a little more closely last night, and found that it's phenyl side groups that make the silicone a good scintillator host, not vinyl side groups. This means that Dow Corning Sylgard 184 is not a good scintillator
host ,unlike what I mentioned at the beginning of this thread. Sigh... It still makes a dandy scintillator-PMT index matcher/glue,though. I will be looking for a phenyl substituted silicone
resin that is transparent. The key to finding one is the info that the phenyl side groups are added to get a resin that is good down to -65 degrees, useful for aerospace applications (look for a low temp silicone...).
I have one candidate from Dow Corning, but the specs differ as to whether the stuff is transparent or translucent, depending on where you look.
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by JohnCuthbert »

Hi
I'm new to this group so please bear with me.
I saw this post a while back and I finally got round to replying.
When I was a student I did some work on fluorescence. I needed a compound that had a fairly long half life and could be made into monomolecular films.
The stuff I used was a europium compound (OK, I realise this is a long name).

Cetylpyridinium Terakis(dibenzoylato europiate(III))

I made it by addinga solution of 2 mMol Europium chloride, 8mMol dibenzoyl methane and 2 mMol cetyl pridinium chloride in 70 ml of alcohol to 4 ml of 2M sodium hydroxide (in water). The product is insoluble so you can just filter it off.
If you were to do this with gadolinium chloride in place of Europium you would produce a gadolinium compound which is soluble in organic solvents. With any luck this means it would disolve in plastic resin.
You might even get away with polystyrene (lots of phenyl groups).
The Europium compound has a fluorescence half life of about a milisecond which might be a problem for you, I don't think so, but I'm not sure. (It emits at 612nm by the way). In any case, I think the half life is a property of the europium so Gd would be different.
It really is a nice easy synthesis. The only thing that smells is the alcohol and most people don't mind that.
Hope this is of some help.
John Cuthbert
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by JohnCuthbert »

Sorry, It had to happen
The stuff is
Cetylpyridinium tetrakis(dibenzolymethanatoeuropiate(II))
Richard Hester
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by Richard Hester »

The Gd chelate is merely a carrier for the gadolinium so that it stays evenly dispersed (and transparent ) in the body of the scintillator. The actual fluor is PPO (with maybe some POPOP as a frequency shifter). Polyphenyl silicone is desirable as the polymer to hold all this junk together, as it can be cast into any shape desired and does not break down or change color under heavy bombardment, not that this is really a problem with a popgun amateur fusor... Polystyrene is a possibility. Tap Plastics sells styrene monomer, ostensibly for mixing in with polyester casting resin. If this stuff can be made to solidify on its own, it may be just the ticket.
By the way, the chelate you describe sounds a little complicated. I may try Gadolinium octanoate first, if the octanoic acid is not too stinky.
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by JohnCuthbert »

You can get styrene to polymerise on its own but go easy on the catalyst or it will get very hot. (you might be able to offset this by dissolving polystyrene in the styrene before polymerising it).
John
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by guest »

Humm ... a new way to do neutron detection , the chemicals seem to be pretty benign Tho a little stinky.
I think pmts could work with it if Popop was included
or a Coumarin dye would work as a phase shifter.
You would want to use a catalyst like dmso in order to get a smooth clear styrene , heat tends into crystal style growth with inclusions unless a uniform heat is used with a very tedious degree by degree cool down
over a twenty hour period.

Very interesting gentlemen,
Just one question when can I buy a Gd schintillator at the trading post?

Larry Leins
Fusion Tech
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by Richard Hester »

Don't expect to find this detector on Ebay any time soon. The basis of this whole thread is a paper from 2 gentlemen at Oak Ridge regarding Gd loaded solid scintillators. Gd has the highest cross section for thermal neutrons all the elements, and it gives off a handsome splash of gammas and conversion electrons when it encounters a neutron. Gd loaded liquid scintillators are nothing new - you can buy a standard Gd-loaded scintillation fluid from either Eljen or Bicron. Solid scintillators are more convenient, and may allow higher Gd loading. Anyway, the scintillator goes into the center of a moderator just like a 3He or BF3 tube would . The difference is that a 1cm thickness of 1-2% Gd loaded scintillator is completely black to thermal neutrons, so it will nab any neutron that trickles its way. This results in a more efficient variant of the moderated neutron detector. Unfortunately, the scintillator will also respond to gammas, but we don't exactly encounter a hailstorm of those in our line of work. Oak Ridge has a patent on their particular implementation of the scintillator, but there is a fair amount of prior art, and more than one way to skin a cat...
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Re: Gadolinium Loaded Scintilaors for Neutron Detection (Double Rats!)

Post by Richard Hester »

It's a long time down the pike (this thread was started in 2002..), but there's some additional information. Zane Bell and company have not stopped plugging away on Gadolinium-loaded thermal neutron scintillators. A 2009 paper from Bell and company mentions Gadolinium isopropoxide as a suitable dopant for styrene-based plastic scintillators. The URL for the abstract is http://www.sciencedirect.com/science?_o ... archtype=a . Not a lot of meat in the abstract, but the mention of gadolinium isopropoxide is interesting. Bell and friends were rather coy in 2002 about their Gadolinium carrier for silicone-based scintillators due to patent issues. I was thinking at the time of using medium-weight fatty acid salts of Gd, but never pursued the matter, as I couldn't locate the proper silicone resin with phenyl side groups (and transparent).
Synthesis of Gd isopropoxide is not too horrible for those with access to proper lab facilities (university foax...). This may be something to watch.
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by lutzhoffman »

Hello:

To take this same principal into the fast neutron region, you can use Arsenic instead of Gd, the isotopes formed have half life decay times around a millisecond max., so real time monitoring is possible. One patent filed on this idea used about 1/2 to one pound of AsO3 in epoxy resin surrounding a plastic scintillator, with a PMT.
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by Richard Hester »

You can work with a pound of arsenic trioxide if you want to - I ain't touching the stuff. Any Gadolinium compound I could imagine would be nectar of the Gods in comparison. What I imagine would be approximately a pencil thickness of Gadolinium-loaded material in the center of a moderator (I have a 6" thick, 12" long rod of HDPE reserved for that purpose) instead of the requisite (and unobtainable) He-3 tube. You may not need even that much thickness for a reasonable detection efficiency.
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by Alyona »

hello,
we have developed gadolinium loaded plastic scintillators up to 2 wt.% of gadolinium
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by Richard Hull »

A resurrected post with no actual tests or reports on this supposed wonderous material related to our fusion efforts. How much is it for a nice sized chunk? Where do you get it? Ordering information? Anyone here actually have some? Tested it?

In the 14 years since the mysterious "guest" posted on this wonderous material, we would expect it to be everywhere and the need for 3He would be a distant, expensive memory.........

Until we see it in our own hands it is so much wind over the decks.

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
Richard Hester
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Re: Gadolinium Loaded Scintiilaors for Neutron Detection

Post by Richard Hester »

I am "guest" - I don't know why the forum stripped the name from some previous posts of mine and not others. As usual, things like this are presented as "items of interest" rather than a be-all and end-all. I was actually interested in something like this a few years ago, especially a Gd-loaded silicone scintillator that could be freely molded. Finding a phenyl-substituted silicone and appropriate Gd donor turned out to be more than I really wanted to handle, given the suspicion that confronts any attempt at amateur chemistry these days (he's buying glassware, he must be making drugs...). I don't know how Zane Bell's efforts actually ended up. As presented, the scintillator would probably still need some gamma/x-ray (x-rays in our case) shielding to inhibit non-neutron events, but it looked cool at the time. These days, I have other fish to fry.
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