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11 Apr

Samples used for radiocarbon dating must be handled carefully to avoid contamination.

Not all material can be dated by this method; only samples containing organic matter can be tested: the date found will be the date of death of the plants or animals from which the sample originally came.

Charcoal is less likely than wood to have exchanged carbon with its environment, but a charcoal sample is likely to have absorbed humic acid and/or carbonates, which must be removed with alkali and acid washes. The constituents of bone include proteins, which contain carbon; bone's structural strength comes from calcium hydroxyapatite, which is easily contaminated with carbonates from ground water.

Removing the carbonates also destroys the calcium hydroxyapatite, and so it is usual to date bone using the remaining protein fraction after washing away the calcium hydroxyapatite and contaminating carbonates. Collagen is sometimes degraded, in which case it may be necessary to separate the proteins into individual amino acids and measure their respective ratios and activity.

Approaching archaeological techniques and artifacts from an interpretive viewpoint, the series looks in detail at specific classes of artifacts that have contributed most to our knowledge of the past, and at particular investigative techniques that are now being used to refine this knowledge and thereby to question previous assumptions.

In Radiocarbon Dating, Sheridan Bowman provides a much-needed introduction to the complex field of carbon dating.

Wood contains cellulose, lignin, and other compounds; of these, cellulose is the least likely to have exchanged carbon with the sample's environment, so it is common to reduce a wood sample to just the cellulose component before testing.

However, this can reduce the volume of the sample down to 20% of the original size, so testing of the whole wood is often performed as well.

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Since it was created after the start of atomic testing, it incorporates bomb carbon, so measured activity is higher than the desired standard.Two common contaminants are humic acid, which can be removed with an alkali wash, and carbonates, which can be removed with acid.These treatments can damage the structural integrity of the sample and remove significant volumes of material, so the exact treatment decided on will depend on the sample size and the amount of carbon needed for the chosen measurement technique.This convention is necessary in order to keep published radiocarbon results comparable to each other; without this convention, a given radiocarbon result would be of no use unless the year it was measured was also known—an age of 500 years published in 2010 would indicate a likely sample date of 1510, for example.In order to allow measurements to be converted to the 1950 baseline, a standard activity level is defined for the radioactivity of wood in 1950.