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Author: Subject: Geiger counter advice please
Lion850
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[*] posted on 17-1-2020 at 02:10
Geiger counter advice please


I want to buy a Geiger counter and I am looking at one listed on eBay with the following link:
https://www.ebay.com.au/itm/Geiger-Counter-Beta-Gamma-X-ray-...

Picture of the listing below. I have no experience with Geiger counters. The reason I want one is to check the radioactivity of my uranyl acetate before I use it and then to check the glassware and so on afterwards. Maybe overkill but just to be sure, and something else to learn about.

If there are members on here knowledgeable about Geiger counter use, can you please comment and tell me if this one will be suitable, or if you perhaps can suggest another model from experience?

Thanks in advance.

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B(a)P
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[*] posted on 17-1-2020 at 02:38


Uranyl acetate is a much bigger concern from an ingestion/inhalation toxicity exposure scenario. It is also mostly an alpha emitter I think? Does that counter pick up alpha? All in all though I don't think radiation will be you issue in handling this substance. I have not had experience handling the substance myself though.
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Lion850
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[*] posted on 17-1-2020 at 02:50


From what I read so far yes it seems the radiation is so low that it is not a concern, but it is indeed toxic inside the body. Thanks for the heads up on the alpha detection. From the eBay data listed alpha is not mentioned, but it does say it can be used to measure uranium.
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Sulaiman
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[*] posted on 17-1-2020 at 03:30


I believe that a small uv lamp (or maybe LED) would cause uranyl salts to fluoresce in the visible/detectable/measurable spectral region.
It could be quite sensitive ? ... in the dark




CAUTION : Hobby Chemist, not Professional or even Amateur
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pantone159
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[*] posted on 17-1-2020 at 07:21


To detect alphas, you need a detector with a thin (mica?) window. Alphas have such low penetration that they will be blocked by anything more substantial. With such a mica window, alphas are picked up easily by a geiger counter.
You will get some gammas from your U, so you should pick up something without the alphas though.
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[*] posted on 17-1-2020 at 10:45


The "specific activity" of uranium is about 25 Bq/mg
So, if very careless washing leaves a whole miligram of uranium on the glassware it will emit about 25 particles per second.
Almost all of that activity will be alpha emission- and the geiger won't "see" it because practically none will get through the plastic case.
Geiger tubes are roughly 1% efficient for gamma detection- generally, the gammas just fly through the detector without "hitting" anything.

So the total best guess is that your mg of uranium would produce about 1 click every 4 seconds.
But at best, only half of them could possibly be expected to go in the "right" direction.
So that's a click every 8 seconds- if the geiger tube is big enough to cover half the glassware.

Realistically, you might hope to get about 1 click per minute due to very dirty glassware.

Even a really good GEiger isn't going to do much better.
Maybe, if you had a good scintillation detector... What's your budget?

Fluorescence with a uv torch or uv LED is a better bet.



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draculic acid69
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[*] posted on 17-1-2020 at 19:26


How much depleted uranium acetate would one need to invest to die? How many milligrammes/grams/Oz would it take? Would you die from heavy metal toxicity or from radiation?
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[*] posted on 18-1-2020 at 01:22


It is not quite as simple as that, as we are all different. It is generally accepted for inhalation that less than 0.05 mg/m3 in air is safe for adults. The immediately dangerous to life and health level is 10 mg/m3. Anything north of that is potentially going to be lethal.
For ingestion LD 50 for rats in 207 mg/kg.
The compound acts on your kidneys and over exposure usually results in death from renal failure.
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[*] posted on 18-1-2020 at 06:33


Quote: Originally posted by draculic acid69  
How much depleted uranium acetate would one need to invest to die? How many milligrammes/grams/Oz would it take? Would you die from heavy metal toxicity or from radiation?

It would almost certainly be the toxicity (rather than the radioactivity) that killed you.
It is difficult to see how this would matter.

This suggests that some bloke survived a gram of the corresponding nitrate
https://www.ncbi.nlm.nih.gov/books/NBK158798/bin/LSE2.pdf

But I'd not like to bet on it.

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Schleimsäure
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[*] posted on 18-1-2020 at 07:43


I have some uranyl acetate. Just be sure to not get it into your system (inhalation, digestion) since its quite soluable in body fluids. The alpha decay would then stay in your body and attack the cells continuously and directly.

It's a weak alpha emitter, so no concerns on its radiation in the environment.
When I use my Geiger/Müller counter on the bottle it goes to up to 180 microSV.
That's basically harmless.
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[*] posted on 18-1-2020 at 07:51


And concerning Geigercounters, they only detect gamma. But also a weak alpha emitter like uranyl acetate emitts some gamma, which will be detected by every Geigercounter.
I think it's like 90% alpha, 6% beta and 4% gamma or something like that.
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Heptylene
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[*] posted on 19-1-2020 at 02:36


A gamma/beta detector isn't ideal for use with uranium salts. Uranium salts contain (almost) only uranium isotopes (238, 235, 234), which are alpha emitters, with little beta and gamma from the small quantities of decay products that have accumulated since manufacture.

Uranium ore on the other hand also contains all the decay products of uranium in secular equilibrium, each of which has an activity equal to that of the uranium isotope it came from. At secular equilibrium, the isotopes are produced as fast as they decay, so their amount doesn't change much over time, and they each contribute equal amounts to the radioactivity (in number of particles emitted per second).

So uranium ore is much more radioactive than pure uranium and we can estimate by how much from the decay chain below.
There are a total of 8 alpha decays and 6 beta decays per uranium 238 atom to reach stable Lead-206. Uranium-238 makes up most of natural uranium and has, by itself, an activity of about 12.5 kBq/mg. That's 12500 decomposition events per second per gram not only for U-238 but also for each decay product, for a combined total of 8x12.5 = 100 kBq/g as alpha particles and 6x12.5 = 75 kBq as beta particles. Almost as much beta as alpha activity!

There's a nice website that explains the principle of secular equilibrium, from which I took the activity plot below. You can see that soon after purification uranium has mostly U-238 and U-234 alpha emission. After years, you start to get beta decays from Th-234 and Pa-234m. And after millions of years you are at equilibrium, hence why this kind of thing only happens in uranium minerals!

(The contribution of the U-235 decay chain is negligible in comparison to U-238, as U-235 has an activity of only about 5% that of U-238 in natural ores)

Additionally, beta particles (which are simply electrons with high energies) can interact with the nuclei of atoms (especially heavy ones such as uranium) to produce x-rays. A phenomenon known as Bremsstrahlung which is used in x-ray tubes for that exact purpose. X-rays are high energy photons, same as gamma rays. The yield of x-rays is low but not zero. So uranium ore produces both beta particles and x-rays in addition to alphas, which is why it can be easily be detected by beta- and gamma-only geiger counters.

If you want to use a geiger counter for safety reasons when using uranium, you should really get one which is sensitive to alpha particles. Especially since uranium chemistry involves purification steps, such that you cannot count on the decay products to make the uranium "visible" to a beta/gamma detector.

Decay chain U.jpg - 116kB

actunat.gif - 7kB
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Lion850
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[*] posted on 19-1-2020 at 22:24


Thanks members for all the info and advice.
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