Dating artefacts

The number of applications of AMS today is large, and so we will focus on a general overview of some interesting applications that will give some flavor for the variety of uses of the method.

Libby’s measurements on C, using samples of several grams of carbon-black powder (see Anderson et al., 1946).

The first attempt to use radiocarbon for dating was the work of Libby and his co-workers, 50 years ago, using counting of the decays of the radioactive isotope.

In the 1950s, gas-counting methods were perfected, and later, liquid scintillation counting has also been used, as we will discuss later.

This article is reproduced from Nuclear News, June 19998, and is based on a paper presented at the ANS Winter Meeting, held November 16-20, 1997, in Albuquerquete N. AMS has become an accurate and precise method for dating many types of materials - including such interesting items as the Shroud of Turin and the Dead Sea Scrolls, which will be discussed later—where only a small sample can be spared.

Accelerator mass spectrometry (AMS) is a technique for direct measurement of the concentration of radioisotopes.

An archaeologist must know the different between an artifact and a fossil.

The practical use of accelerator mass spectrometry was shown in 1977 by two groups simultaneously at Mc Masversity and at the universities of Toronto and Rochester (N. The great advantage of using AMS is that we can measure the isotope ratio of C to stable carbon directly.

By the end of 1997, some two dozen AMS laboratories were in operation around the world, with more in the planning stages.

C produced in the atmosphere were always the same, then we could calculate a "radiocarbon age" using the equation we have discussed directly as an estimate of sample age. This was recognized soon after Libby published his first Curve of Knowns (Arnold and Libby, 1949).

When a C atom decays, it emits a beta particle, which can be counted in a gas by the electrical pulse it generates.

In a liquid scintillation counter, the beta particle excites the emission of light from a complex organic molecule or "scintillant." Because only about 13.5 decays per minute occur in one gram of modern carbon, it was necessary to use fairly large samples of several grams of carbon.

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