Atmospheric C14 is measured permil Permil of what?

[Calvadosser]

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

 

[tiny-tim]

Hi Martin!

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" …

see http://en.wikipedia.org/wiki/Per_mil

 

[beee]

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".

 

[Calvadosser]

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.