5 ms·

Half-life seems to short, only ~88 years.

philipkglass 4y ago
You appear to be referring to plutonium 238. This work analyzes the ratio between plutonium 239 and 240, which respectively have half lives of 24110 years and 6561 years. https://en.wikipedia.org/wiki/Isotopes_of_plutonium#List_of_isotopes https://en.wikipedia.org/wiki/Isotopes_of_plutonium#List_of_...
- mjevans 4y ago
  Unless it's a post WW-whatever-we-nuked recovery of humans or an offshoot again, the 6500 years halflife sounds likely to expire before a new scientifically intelligent species arises. Though I really hope things don't come to that.
  - dredmorbius 4y ago
    Probably correct. In most cases, isotopes can be detected for up to about ten half-lives, after which prevalence is reduce to 1/1,000th the initial concentration. In this case, that would be about 240,000 to 650,000 years. For comparison, h sapiens seems to have diverged from its common ancestor to the other great apes about 2 million years ago, and achieved modern anatomical form about 200,000 years ago. The period 240kya -- 650kya corresponds roughly to h. heidelbergensis. https://en.wikipedia.org/wiki/Homo_heidelbergensis https://en.wikipedia.org/wiki/Homo_heidelbergensis The well-known organic-material radiodating isotope carbon-14 has a half-life of about 5,730 years, and is effective in dating materials to about 60,000 years ago. We're going to need a bigger boat ^W^W longer half life. Probably on the order of 200,000 to 10 million years.
    - kolinko 4y ago
      But even if we cannot detect the original plutonium, we could detect the product of it’s decay - right?
      - dredmorbius 4y ago
        For dating what's necessary is to measure the ratio of the elements. Daughter / decay elements of plutonium don't indicate the initial quantity, and might (I'm not sure of this) also be the result of other decay chains. Radiodating used to determine the age of the Earth relies on uranium-lead dating using samples found within zircon crystals. The crystals cannot form in the presence of lead, so any lead found within a crystal must have appeared there after the crystal formed. As both the mother uranium and daughter lead are within the same sample, the ratio can be clearly determined. https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating Absent a similar containment for plutonium in the formations being described in TFA, that may not be possible. For C-14 dating, the ratio of carbon isotropes within living tissue is known. The residual C-14 is what's left after the original organism has died, and the ratio then determines age. Given the short timespans afforded by C-14 dating, concerns with contamination or loss are lower.
idiotsecant 4y ago
Oh, well there goes any small comfort, into the void then!

You appear to be referring to plutonium 238. This work analyzes the ratio between plutonium 239 and 240, which respectively have half lives of 24110 years and 6561 years. https://en.wikipedia.org/wiki/Isotopes_of_plutonium#List_of_isotopes https://en.wikipedia.org/wiki/Isotopes_of_plutonium#List_of_...

mjevans 4y ago
Unless it's a post WW-whatever-we-nuked recovery of humans or an offshoot again, the 6500 years halflife sounds likely to expire before a new scientifically intelligent species arises. Though I really hope things don't come to that.
- dredmorbius 4y ago
  Probably correct. In most cases, isotopes can be detected for up to about ten half-lives, after which prevalence is reduce to 1/1,000th the initial concentration. In this case, that would be about 240,000 to 650,000 years. For comparison, h sapiens seems to have diverged from its common ancestor to the other great apes about 2 million years ago, and achieved modern anatomical form about 200,000 years ago. The period 240kya -- 650kya corresponds roughly to h. heidelbergensis. https://en.wikipedia.org/wiki/Homo_heidelbergensis https://en.wikipedia.org/wiki/Homo_heidelbergensis The well-known organic-material radiodating isotope carbon-14 has a half-life of about 5,730 years, and is effective in dating materials to about 60,000 years ago. We're going to need a bigger boat ^W^W longer half life. Probably on the order of 200,000 to 10 million years.
  - kolinko 4y ago
    But even if we cannot detect the original plutonium, we could detect the product of it’s decay - right?
    - dredmorbius 4y ago
      For dating what's necessary is to measure the ratio of the elements. Daughter / decay elements of plutonium don't indicate the initial quantity, and might (I'm not sure of this) also be the result of other decay chains. Radiodating used to determine the age of the Earth relies on uranium-lead dating using samples found within zircon crystals. The crystals cannot form in the presence of lead, so any lead found within a crystal must have appeared there after the crystal formed. As both the mother uranium and daughter lead are within the same sample, the ratio can be clearly determined. https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating Absent a similar containment for plutonium in the formations being described in TFA, that may not be possible. For C-14 dating, the ratio of carbon isotropes within living tissue is known. The residual C-14 is what's left after the original organism has died, and the ratio then determines age. Given the short timespans afforded by C-14 dating, concerns with contamination or loss are lower.

idiotsecant 4y ago

Oh, well there goes any small comfort, into the void then!