Atmospheric C14 is measured permil Permil of what?

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Discussion Overview

The discussion centers around the measurement of atmospheric radiocarbon (C14) expressed in "permil" and seeks to clarify what this measurement is relative to, particularly in the context of its decline since atmospheric nuclear testing ended. Participants are exploring the implications of these measurements and their conversion into absolute units.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions what "permil" refers to in the context of atmospheric C14 measurements, expressing a desire to understand its absolute units.
  • Another participant suggests that the measurement could refer to either "per thousand" or "per million," indicating uncertainty about the terminology.
  • A different participant proposes that the measurement is typically a ratio to stable C12, leaning towards "per thousand" based on referenced materials.
  • One participant expresses confusion regarding the high values of C14 measurements and the use of the symbol "0/00," which indicates parts per 1000, but remains unclear about what it is parts per 1000 of.

Areas of Agreement / Disagreement

Participants exhibit uncertainty regarding the definition of "permil" in this context, with multiple competing views on whether it refers to "per thousand" or "per million." The discussion remains unresolved.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the definitions of "permil" and the lack of clarity on the reference standard for the C14 measurements.

Calvadosser
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Atmospheric C14 is measured "permil". Permil of what?

I'm interested in understanding how the level of atmospheric radiocarbon has declined since atmospheric nuclear testing ended. Please excuse my ignorance of what is no doubt something extremely elementary.

Atmospheric C14 measurements are available - for example http://scrippsco2.ucsd.edu/data/flask_co2_and_isotopic/daily_iso/mlo_c14indiv.csv These tables give "Atmospheric Delta-14C (permil) derived from flask air samples."

The measured C14 is given as "permil" but I don't know what it is permil of.

Please help me understand what this means, so I can convert the measurements given into absolute units. Thank you for your help.

Martin
 
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Hi Martin! :smile:
Calvadosser said:
Atmospheric C14 measurements are available - for example http://scrippsco2.ucsd.edu/data/flask_co2_and_isotopic/daily_iso/mlo_c14indiv.csv These tables give "Atmospheric Delta-14C (permil) derived from flask air samples."

Unfortunately, there is no way of being sure whether it means "per thousand" or "per million" :rolleyes: …

see http://en.wikipedia.org/wiki/Per_mil :redface:
 
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I believe it is usually given as a ratio to stable C12.

As for "per thousand" vs "per million", judging by the Wiki article referenced by tiny-tim, it is "per thousand". Another pointer to that is that in the tabulated data provided includes another quantity which is expressed as "ppm" which is explicitly "per million".
 


Beee - thanks for that. I also thought it probably was relative to C12 - but the values go up to 900 in some C14 measurements. The symbol "0/00" is used sometimes - definitely indicating parts per 1000.

So I'm still puzzled what it is parts per 1000 of.
 

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