The first example deals with radiocarbon dating. The concept is kind of simple:. Every living being exchanges the chemical element carbon during its entire live. But carbon is not carbon. It consists almost on Carbon the stable nuclide but to a certain amount on Carbon, too. In nature the ratio is approximately constant due to a continuous production of in the earth atmosphere by cosmic rays.
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Radiocarbon dating - Wikipedia
Radiocarbon dating also referred to as carbon dating or carbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon , a radioactive isotope of carbon. The method was developed in the late s at the University of Chicago by Willard Libby , who received the Nobel Prize in Chemistry for his work in It is based on the fact that radiocarbon 14 C is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14 C combines with atmospheric oxygen to form radioactive carbon dioxide , which is incorporated into plants by photosynthesis ; animals then acquire 14 C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14 C it contains begins to decrease as the 14 C undergoes radioactive decay. Measuring the amount of 14 C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14 C there is to be detected, and because the half-life of 14 C the period of time after which half of a given sample will have decayed is about 5, years, the oldest dates that can be reliably measured by this process date to around 50, years ago, although special preparation methods occasionally permit accurate analysis of older samples.
Calculation of radiocarbon dates
Radiocarbon dating methods produce data that must then be further manipulated in order to calculate a resulting "radiocarbon age". The calculations to be performed on the measurements taken depend on the technology used, since beta counters measure the sample's radioactivity, whereas accelerator mass spectrometers AMS determine the ratio of the three different carbon isotopes in the sample. The calculations to convert measured data to an estimate of the age of the sample require the use of several standards. To compensate for this, the measurements are converted to the activity, or isotope ratio, that would have been measured if the sample had been made of wood. The details of the calculations for beta counting and AMS are given below.
Radiocarbon dating is achieved by two methods. The traditional " Beta-counting " method is based on the detection of radioactive decay of the radiocarbon 14 C atoms. These techniques are made possible by sensitive electronic instruments developed in the late twentieth century. Both methods rely on the ongoing production of radiocarbon in the upper atmosphere.