The Naked Scientists

The Naked Scientists Forum

Author Topic: What is the process through which carbon-14 is generated?  (Read 7337 times)

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
How is the carbon 14, which is used in radiocarbon dating, made in the atmosphere? What is the physical / chemical process by which this occurs?


 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
What is the process through which carbon-14 is generated?
« Reply #1 on: 06/04/2008 17:10:52 »
From Nitrogen and thermal neutrons:

1n + 14N → 14C + 1H

On earth it occurs from cosmic rays in the upper atmoshere
« Last Edit: 06/04/2008 17:12:31 by graham.d »
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
What is the process through which carbon-14 is generated?
« Reply #2 on: 13/04/2008 22:01:52 »
So where do the neutrons come from in the first place?
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
What is the process through which carbon-14 is generated?
« Reply #3 on: 15/04/2008 14:05:27 »
They result (for example) from a high energy cosmic ray proton colliding with an atom's nucleus. This can produce a Neutron and a bunch of mesons. This happens in the upper atmoshere. There is a resulting flux of neutrons passing through us all the time, but they don't have a large collision cross section.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
What is the process through which carbon-14 is generated?
« Reply #4 on: 18/04/2008 09:21:16 »
Thanks Graham. And what's a meson, by the way?
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
What is the process through which carbon-14 is generated?
« Reply #5 on: 18/04/2008 11:07:07 »
Oh heck! It is best to type "meson" into Google and look up the answers. Wikipedia is quite good. Mesons are one of many particles that make up our universe and there are quite a few types, some charged, some not. This is where it gets into the realm of particle physics and can get very complicated.
 

another_someone

  • Guest
What is the process through which carbon-14 is generated?
« Reply #6 on: 18/04/2008 11:54:18 »
They result (for example) from a high energy cosmic ray proton colliding with an atom's nucleus. This can produce a Neutron and a bunch of mesons. This happens in the upper atmoshere. There is a resulting flux of neutrons passing through us all the time, but they don't have a large collision cross section.

I would have thought we'd get a large flux of neutrons coming at us from the Sun (as a byproduct of thermonuclear burning) - or have most of the neutrons already decayed by the time they have gotten to us?
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
What is the process through which carbon-14 is generated?
« Reply #7 on: 18/04/2008 14:01:25 »
You raise a very good question. The half life of a neutron is only 10.3 minutes so the only neutrons that can reach the earth from the sun are high energy neutrons. These would have a low collision cross section as a result of this and most would pass rapidly through the atmosphere and deeply into the earth (or its oceans) before managing to interact with anything. The presence of neutrons in space borne radiation is a subject of significant research still and there seems to be evidence that the neutron flux is higher following solar flare activity. Again it is all high energy neutrons. The amount these contribute to Carbon14 production is open to debate although I would say it is likely that it is still the secondary neutron production that is the main source.
 

The Naked Scientists Forum

What is the process through which carbon-14 is generated?
« Reply #7 on: 18/04/2008 14:01:25 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums