RE: C14 Natural abundance

["Broseus, Roger" <rbroseus@exchange.nih.gov>]

	Edward wilds asked:

	----------
	From: 	Edward L. Wilds, Jr.[SMTP:wilds@safety.ehs.uconn.edu]
	Sent: 	Thursday, October 09, 1997 10:55 AM
	To: 	Multiple recipients of list
	Subject: 	C14 Natural abundance

	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: try NCRP Report No. 81, Carbon-14 in the Environment (1985).

Of course the abundance of C-14 in the "environment" varies and it
predictable, hence our ability to do carbon dating.  In the atmosphere,
the majority of C-14 is present due to natural production from cosmic
ray interactions in the atmosphere.  The specific activity is decreasing
due to the "Suess effect," dilution by carbon from combustion of fossil
fuels which have no C-14.

According to the above report, in Table 2.1, the abundance of C-14 in
the atmosphere is 10 to the minus 10th percent.  That works out to .000
000 000 1%.

/Roger W. Broseus
RogerB@nih.gov