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Re: C14 Natural abundance
NCRP 81, "Carbon-14 In The Environment" quotes a specific activity for
cosmogenic C-14 in the atmosphere of 6pCi/gC. In addition, there are varying
levels due to weapons tests and other manmade sources.
However, I think that you are asking the wrong question. The % abundance of a
radioactive isotope is usually asked regarding "primordial" radionuclides,
which are long lived radionuclides that were present at the creation of the
universe. These include Th-232, U-238, K-40, and Rb-87. Since C-14 has a
half life of "only" 5730 years (versus 1.28 E9 years for K-40, for example),
any C-14 present at the creation is long gone. The reason that we find it in
the environment as "natural background" radioactive material is that it is
continually being produced, by both manmade processes, such as nuclear
weapons, as well as by natural processes, such as cosmic rays. NCRP 50,
"Environmental Radiation Measurements" states that the "rate of atmospheric
production of atoms" for C-14 is 2.5/(cm2 sec).
The opinions expressed are strictly mine. Here's to a risk free world, and
other fantasies.
Bill Lipton
liptonw@detroitedison.com
Radsafers:
Can someone complete the following table for the natural
abundance of carbon isotopes in the environment and supply the
reference.
C12 - 98.89%
C13 - 1.11%
C14 - ?
I have seen a value for C14 of 0.0000000010%. Is this familiar
to anyone? Thanks for the help.
Ed Wilds
+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*++*+*+*+*+*+*+*+
Edward L. Wilds, Jr., Ph.D.
The University of Connecticut
Department of Environmental Health & Safety
Radiation Safety Manager
233 Glenbrook Rd., U97
Storrs, CT 06269-4097
Ph. (860) 486-3613
Fax.(860) 486-1106
Email: Ehsadm3@uconnvm.uconn.edu
Wilds@safety.ehs.uconn.edu