Fw: C-14 radiocarbon from academic perspective

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--- On Tue, 30/6/09, ishwar33 <ishwar33 wrote:

 

Dear Chandrasekhar Phadke,

 

Thanks for your informative article on C-14 radiocaron dating on archeological artifacts and you also mentioned that antique metalic items which were created in were in use since then does not contain the enough carbon to be dated.

 

The dating is done using normal C14 assay or C-14 AMS (Accelerator Mass Spectrometry) . For samples with very less c-14 carbon and small sample size the C14-AMS is preferred and there is no lab in India who can do C14-AMS. There is only one conventional dating lab in lucknow, headed by Dr. Chandra Mohan Nautiyal. The C-14 AMS labs can be found at http://www.radiocar bon.org/Info/ ams-labs. htm

 

What is c-14 radiocarbon dating?

 

The C-14 is formed by interaction of cosmic radiation with N-14 (Nitrogen 14) .

The abundant c-12, rare c-13 and radioactive c-14 is aborbed by living organism. The c14 is so rare that only 1 atom of c-14 is present per every trillion. After the death of living organisms the amount of c14 begins to decrease. A C-14 date estimates the time since the death of once-living things, upto about 50,000 years. The c14 in dead organism slowly decays to N-14, the mechanism is called beta decay. The rate, as for all radioactive decay, is related to the amount of C-14 present at any given time, in principle any material that still has a sufficient amount of c-14 can be dated, with the date representing the time since the material since the material stopped exchaning carbon with atmosphere. For example the percentage of c-14 left after 3 half-lifes of time have gone by is 12.5 %. The half-life of c-14 is 5730 years (normaly rounded to 6000 years). A sample that has decayed for 3 half-lifes is 3 x 5730 years or 17190 years old.

 

There is nothing called c13 assay test, but The deltaC13 is a notation to indicate the stable carbon isotoopic composition (deviation of C-13/C-12 ratio in the sample from a standard;(it' s multiplied by 1000 to make it comfortable to deal with). It's not related to the measurement of C-14 which is, in contrast, radioactive. The value of deltaC-13 is, however, used to make a correction on C-14 date.

 

I also got confirmation from Dr. Alexander Cherkinsky at

Center for Applied Isotope Studies,University of Georgia that brass, bronze, silver and silver alloys cannot be dated using c14-AMS or other dating methods due to nil carbon content.

 

Regards,

Ishwar

 

 

 

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