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Isotopic Analysis

Isotopic Analysis

Varieties of the same chemical element, but with different atomic weights, are called isotopes. Isotopic analysis (IA) is the analysis of the isotope composition of a sample. Samples in IA can contain almost anything: different objects of everyday life, pieces of rocks, pieces of wood, samples of tissue taken from a human body, chemical compounds, and so on. In general, isotopic analysis is used for identification of a sample and for the determination of its age. Determining the age of an object can be important in a forensic examination, especially when examining human remains from cold cases, ancient sites, or mass graves. Isotopic analysis is based upon the use of mass spectrometers or radioactive radiation counters. A mass spectrometer is a device that determines the quantity and composition of different isotopes (of the same chemical element as well as various elements) in the sample.

The isotope composition of many objects is unique (relative to the composition itself as well as to the isotope concentrations), and because of this, isotopic analysis offers the possibility for identification of a sample. Isotopic analysis is also utilized in varying disciplines, including chemistry, medicine, biology, geology, archeology, and criminal forensics. Recently, isotopic analysis has seen use in the diagnosis of some diseases through analysis of air exhaled by the patient. Often, isotopic analysis permits the scientist to distinguish the genuine product from its imitation. For example, the technology is used to distinguish expensive types of wine and liquor from their imitations.

Isotopes can be both stable and radioactive. Isotopic analysis of radioactive isotopes permits scientists to determine the age of the investigated sample. Often the isotope 14C (carbon-14) is used for this purpose. This isotope itself is unstable and decays with time, and in the decay process, other stable isotopes are created. In nature, the concentration of 14C is maintained because of cosmic radiation. While a tree lives, for example, the concentration of 14C in its wood is equal to the 14C concentration in the environment, because atoms of radioactive carbon penetrate the wood from the atmosphere with carbon dioxide (CO2) molecules due to photosynthesis, and also through the tree root system. But when the tree dies, these exchange processes cease, and the 14C concentration in the tree begins to decrease. The law of radioactive carbon concentration alteration in the sample is known, hence if its concentration is measured in the sample and compared with the concentration of the isotope in nature, the age of the tree itself can be determined (or more precisely, the time since the tree died). When the decay period of the radioisotope is considered, the age of the sample can be determined within an accuracy of several decades.

Alexandr Ioffe

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