Assertion: carbon | /r/HasProperty | counted
Facets:
Source sentences:
text: The definition of radiocarbon years is as follows: the age is calculated by using the following standards : a) using the Libby half-life of 5568 years, rather than the currently accepted actual half-life of 5730 years; (b) the use of an NIST standard known as HOxII to define the activity of radiocarbon in 1950; (c) the use of 1950 as the date from which years "before present" are counted; (d) a correction for fractionation , based on a standard isotope ratio, and (e) the assumption that theratio has not changed over time. ^