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How to decide ancient wood time
From;    Author:Stand originally
A kind of method that archaeologist determines Gumunian is acting is to use a radio isotope to regard “ clock as ” , will measure long time, this calls a radio isotope ancient bronze mirror year law.
The carbon in nature basically is 12C, also have a few 14C, it is the generation below the effect that the high-energy particle that the nucleus in high-level air shoots in the sun spreads. 14C is to have emissive carbon isotope, can undertake β disintegration initiatively, become nitrogen, half-life is 5730.

14C atom arises ceaselessly ceaseless disintegration, achieve dynamic balance, its content in atmosphere is stable, there is a 14C in 1012 carbon atom about. Vivid plant carries photosynthesis and respiration and element of environmental exchange carbon, in the scale of the 14C inside body and air identical.

The plant is withered after dying, the 14C inside remains still is undertaking disintegration, decrease ceaselessly, but get complement no longer. Accordingly, the circumstance that reduces according to radioactivity intensity is OK the time that cipher out plant dies.

For example, should conclude the time of a Gu Mu, can add Gu Mu first lukewarm, make the sample of carbon extraction 1g, reoccupy particle tally undertakes metrical. If be measured sample is minutelily,the time just in time of disintegration is the in part that modern plant institute makes sample, show this Gu Mu passed a half-life of 14C, namely 5730. If be measured minutelily,the frequency of disintegration is other value, also can give Gu Mu's time according to half-life computation.

Worker of our country archaeology uses radio isotope ancient bronze mirror year the law piles fir of cover board of the outer coffin outside a Chinese grave to undertake metrical to Ma Wang, the result shows this grave is apart from today 2130±95 year. Carry historical literature textual research, the time of this barrow is the Western Han Dynasty inchoate, it is about before 2100, both accord with very well.

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