A history of radiometric dating.

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Gfamily
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A history of radiometric dating.

Post by Gfamily » Mon Nov 07, 2022 3:57 pm

Interesting read.
https://physicstoday.scitation.org/do/1 ... 20221104a/

I think I need to think about how precisely this method works
In the isotope dilution method used today, scientists take highly enriched 235U and dissolve it, calibrating the liquid so they know the precise concentration. They add that solution to a similar mixture of dissolved rock, homogenizing the two. By then measuring the ratio of the two uranium isotopes in the mixture, they can learn how many atoms of natural uranium—with its known ratio of 235 to 238—are in the sample.
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Re: A history of radiometric dating.

Post by Boustrophedon » Tue Nov 08, 2022 10:43 am

A mass spectrometer will give you a peak, but that doesn't tell you how much of it was in the sample. Give the sample a known amount of U235 then you have a reference peak to compare the U238 in the sample with.
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Re: A history of radiometric dating.

Post by shpalman » Tue Nov 08, 2022 11:15 am

Nope, still not convinced. How does adding a known enriched ratio of U235/U238 to the sample help you figure out the U235/U238 ratio in the sample more easily or more precisely than just measuring the U235/U238 ratio in the sample directly?
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Re: A history of radiometric dating.

Post by dyqik » Tue Nov 08, 2022 2:00 pm

shpalman wrote:
Tue Nov 08, 2022 11:15 am
Nope, still not convinced. How does adding a known enriched ratio of U235/U238 to the sample help you figure out the U235/U238 ratio in the sample more easily or more precisely than just measuring the U235/U238 ratio in the sample directly?
I think it's by giving a "gain" calibration (radioastronomy terminology) and determination of the background to the spectrum, so that you can calibrate the height/area under the peaks due to the sample vs that area due to the background.

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Re: A history of radiometric dating.

Post by shpalman » Tue Nov 08, 2022 2:09 pm

Oh it's because you want the absolute number of U235 and U238 atoms in the sample, so if you add a known number of atoms of mainly U235 and a bit of U238, you can tell if there were a lot (your spike didn't make much difference) or not many (your spike made a big difference). And you can tell how much of a difference your spike made to the sample from your measurement which is actually telling you how big a difference the sample made to your spike.
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Re: A history of radiometric dating.

Post by KAJ » Tue Nov 08, 2022 2:44 pm


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Re: A history of radiometric dating.

Post by shpalman » Tue Nov 08, 2022 3:48 pm

KAJ wrote:
Tue Nov 08, 2022 2:44 pm
See https://en.wikipedia.org/wiki/Isotope_dilution
I did.
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Re: A history of radiometric dating.

Post by Bird on a Fire » Sat Nov 12, 2022 12:27 pm

IIRC that's also used for stable isotope analysis, at least for trace elements that go in the mass spec. A while since I did any, though, and the uni has a technician to do the fancy physics bits ;)
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Re: A history of radiometric dating.

Post by KAJ » Sat Nov 12, 2022 4:21 pm

Bird on a Fire wrote:
Sat Nov 12, 2022 12:27 pm
IIRC that's also used for stable isotope analysis, at least for trace elements that go in the mass spec. A while since I did any, though, and the uni has a technician to do the fancy physics bits ;)
Yes, that's where I've seen it used. The Wiki article I cited above says
https://en.wikipedia.org/wiki/Isotope_dilution#Applications wrote:... In addition to the use of stable isotopes, radioactive isotopes can be employed in isotope dilution...

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