Re: Fooling radiocarbon dating

Thanks Maty and OG. Both have improved my knowledge of the subject.

Harry C.


OG wrote:
<mmeron@xxxxxxxxxxxxxxxxxx> wrote in message
news:CoJch.21$45.356@xxxxxxxxxxxxxxxxxxxx
In article <1165185036.728190.113660@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"hhc314@xxxxxxxxx" <hhc314@xxxxxxxxx> writes:
Mati, an honest question for you.

In radiocarbon dating, how exactly is the carbon baseline determined
and secondly, how is radioactive contamination from other sources other
than C14 eliminated?

I was newver directly involved in this so I can only offer guesses.
As I see it, the best way to establish a baseline would be by using a
(large) number of objects the age of which can be well established by
independent means. As for contamination from other sources, well,
relying on actually counting the decays is rather imprecise since the
decay is beta, thus spectroscopy is less accurate than for gammas. I
think that there aren't many natural sources in an energy range close
to this of C14 but betas inherently don't have a sharp spectrum so
contamination cannot be ruled out. Modern techniques, AFAIK, rely not
on decay counting but on accelerator mass spectroscopy where you
vaporize a sample and count ions of each mass. You need a good enough
mass resolution to distinguish C14 from N14 but that's easily done
nowadays.

Again, I've no direct experience, but I would have thought that chemical
reactions would be performed to produce pure CO2 from the sample that would
then be subjected to mass spectrometry to measure the proportion of C12 to
C14. Ensuring N14 does not contaminate the mass spectrometer result is only
dependent on the rigour of the chemical processes.

C14 dating was initially done on the basis of current relative abundances in
the atmosphere and in living organic materials and dating was done by
measuring the reduction in C14 abundance in historic samples using the known
half-life of 5730 years.

Later studies using tree ring data dating back to several thousand years ago
led to revision of the assumption of constant atmospheric C14 amounts (I
think this was referred to as calibration in the recent C14 thread), and
hence an improvement in the accuracy of the measurement of sample ages using
C14.

I believe that ice core samples include trapped air bubbles that allow
direct measurement of historic C14 abundances (adjusted for half life
losses) which improves the scale further.

.

Relevant Pages

  • Re: Fooling radiocarbon dating
    ... In radiocarbon dating, how exactly is the carbon baseline determined ... As for contamination from other sources, well, ... to this of C14 but betas inherently don't have a sharp spectrum so ... on decay counting but on accelerator mass spectroscopy where you ...
    (sci.physics)
  • Re: Study Re-evaluates Evolution of Mammals
    ... Just look at how well C14 results that were "concrete" have just been ... radiocarbon dating is no good beyond 50 000. ... to fossils where all the carbon has been replace by other minerals. ... derdag so stipulates that derdag isn't accurate about methods of C14 ...
    (talk.origins)
  • Re: Carbon-14 fallacy in dating
    ... C14 are not reliable anyway, ... "Why did it start with no C-14, when it had, apparently, lots of all ... "C-14 dating is calibrated using tree-ring dates back to over 8,000 ... and the necessary correction amounts to only a few ...
    (talk.origins)
  • Re: Study Re-evaluates Evolution of Mammals
    ... Just look at how well C14 results that were "concrete" have just been ... C14 dating due to this, ... how much carbon-14 you have to begin with, after 5760 years half of it ... Derdag, if in fact you 'learned enough' about C14 to critically ...
    (talk.origins)
  • Re: Study Re-evaluates Evolution of Mammals
    ... immediately clear the way for the rise of today's mammals. ... I learned enough about it to see that my position on C14 hasn't ... C14 dating due to this, ... Recalibration of radiocarbon dating has been going on for decades. ...
    (talk.origins)