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Author: Subject: Extracting thorium daughters from Th compounds
Stibnut
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[*] posted on 25-2-2017 at 11:44
Extracting thorium daughters from Th compounds


I've ordered and received a gram of thorium nitrate, which is water-soluble, from United Nuclear. I’ve dissolved 0.69 g of the Th(NO4)4 in H2O. I also have about two grams of thorium dioxide, 1 g from an earlier UN purchase and ~1g extracted by dissolving TIG electrodes in H2O2, along with a chunk of monazite.

What I would like to do is to separate out some of the daughters in thorium's decay chain from the thorium itself, and then measure their half-lives and do some experiments on them while they last. For detection, I have an Inspector Geiger counter sensitive to alpha, beta, and gamma, and also an AtomSpectra gamma spectrometer, a fairly cheap Russian-made NaI(Tl) tube. The gamma spec is nothing fancy but it can pick out a few of the most gamma-active daughters from my ThO2 – most notably Ac-228, Pb-212, and Tl-208.

Here is the full decay chain. The longest half-life in the whole chain is Ra-228, at 5.75 y. This is great because it means that any thorium compound that wasn’t made super recently will have detectable amounts of the entire decay chain. Using my gamma spec, I can detect all of the gamma-active ones in both the ThO2 and the Th(NO3)4. Contrast this with U-238, where U-234 (246000 y) and Th-230 (75300 y) stop anything after them from appearing in detectable quantities in uranium compounds; you’d have to crush up some ore to get the rest of the chain.

I mostly want to separate out the gamma emitters – there are three really good ones that stand out on a gamma spec. First is Ac-228, with major peaks at 338, 911, and 968 keV and a half-life of 6.25 h. If I could separate the Ra-228 from the Th, I could use it as an Ac-228 generator.

How might I separate out Ra from Ac and Th? My impression of alkaline earth chemistry is that it’s pretty similar to lanthanide and actinide chemistry, except for the +2 oxidation state in place of +3 and +4. So nothing is really coming to me. From reading about thorium nitrate, it appears that it can be precipitated out with oxalic acid, which I have. But there’s also a barium oxalate and presumably a radium one which are also insoluble.

The other two of interest are Pb-212 (10.64 h) and Tl-208 (3 min, preceded by Bi-212 [1 h]). I might be able to get these puppies by adsorbing Rn-220 (56 s) onto activated carbon, then crushing it up and extracting the Pb-212 before it decays. I’m not sure how to get lead out of activated carbon, though.

So, does anyone have any tips about how to separate lead, bismuth, radium, and thorium from each other? I'm looking in bur's thread about radium extraction from ore now too.
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[*] posted on 26-2-2017 at 02:43


Th has a long half life. The fraction of it that will have decayed since it was extracted + sold to you is small.
So the quantity of daughter products will also be small. However that idea is made more complex because one of the daughter products is a Th isotope. So you will have some of the other daughters from that.

You might be able to isolate the Radium by co precipitation of the sulphate with barium

The only thing where you will find all the daughters in the "proper" equilibrium amounts is the monazite.
It goes without saying that all of these are nasty things to work with.
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[*] posted on 26-2-2017 at 13:43


It's not so much thorium's long half-life that matters as it is the half-lives of everything below it in the decay chain. Even granted a 14 billion year half life, it still decays at 4070 Bq/g. Supposing I have 1 gram of Th, it gives off 10^8 decays per month. The half-life of its daughter Ra-228 is 5.75 y, which is fast enough that it should be possible to measure substantial buidup over time, via the short-lived gamma-active Ac-228. But of course it does decay into Th-228, which can't be separated from the 232 and will cause some problems. Still, I'm thinking that if I can get Ra-228 on its own, away from both the Th-232 and Th-228, I should eventually be able to see the rest of the decay chain slowly develop.

Thanks for the idea on co-precipitating with barium. I'll try that ASAP.

I'm definitely not expecting anything like equilibrium concentrations; that would take ~50 years after the Th compound was initially synthesized. I mostly just want to see if I can get clear gamma spec and Geiger signals of the various daughters. I'm encouraged by the fact that, when I used my gamma spec on the total sample, the major gamma-emitting Th daughters down to Tl-208 were all clearly visible, albeit probably nowhere near equilibrium unless it had been part of some old stockpile or something.

[Edited on 27-2-2017 by Stibnut]
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