They are then in the drift chamber, which allows the measurement of the electric current of both types of ions. There they are accelerated and hit the analysing magnet. Carbon ions (produced in the ion source) are directed to the accelerator. To determine the ratio of individual carbon isotopes, the AMS spectrometer measures the 14C, 13C i 12C atoms that are released from the cathode (made of the test material). The device can be divided into a low-energy and a high-energy part. They are entirely a uniform high-vacuum chamber of a length of about 15 meters. The various components of this apparatus, such as the ion source, accelerator, analysing magnet or electrostatic analyser are placed along the sides of a 5 x 5 m square.
Accelerator mass spectrometers are used in the AMS technique. A parallel measurement of the 13C content is also made. The accelerator technique, AMS, exploits the fact that 14C is slightly heavier compared to 12C (about 1.17 times). Measurement of the content of radioactive carbon 14C in the material is complicated and requires specialized equipment, which makes the whole process expensive. AMS technique for measuring radiocarbon concentration, 14C The conventional radiocarbon age is determined by comparing the content of both carbon isotopes in the test sample and in the modern biosphere standard. Comparison of the ratio of the content of 14C and 12C in the dead organic matter and in the atmosphere allows to determine the radiocarbon age (the time from the death of the organism to the moment of measurement). The quoted assumption became the basis for determining the age of archaeological finds, which is called radiocarbon dating (or the radioactive carbon method). The decay of this isotope takes place at a rate determined by the law of its decay (the decay of 14C atoms over time takes the form of an exponential function). When an organism dies, it no longer takes up carbon 14C, so its amount steadily decreases. Then the content of the 14C isotope is constant. Organisms participate in the radiocarbon exchange cycle with the biosphere. Carbon dioxide containing radioactive 14C penetrates into all living things – plants and animals. One of the most important applications of the 14C isotope is so-called radiocarbon dating. With its help, it is possible to track changes that occur in the natural environment. Thus, it becomes a natural isotope tracer. The concentration of the 14C isotope in the atmosphere is several times higher than, for example, in the depths of the ocean. They assimilate in plants or are dissolved in ocean water. 14C radiocarbon is a component of many organic compounds. Carbon dioxide, 14CO 2, in turn, is released from the atmosphere into the biosphere and hydrosphere (as a result of, for example, diffusion, dissolution, photosynthesis). When this form reacts with the hydroxyl radical (OH), it is further oxidized to 14CO 2. Radiocarbon datingĪ large part of the carbon isotope 14C, which is accumulated in the atmosphere, is oxidized to form 14CO. Thus, after this time, from one portion of radioactive 14C remains half of it. For the 14C isotope of carbon it is 5730 years. The time after which the content of radioactive carbon decreases by half is defined as the half-life (characteristic of radioactive elements).
The intensity of the radiation it produces also decreases. Over time, the content of radioactive 14C isotopes in the material decreases. Beta decay produces non-radioactive nitrogen 14N, an electron, and an antineutrino.
The carbon isotope 14C decays spontaneously. Its source is the nuclear reactions of thermal neutrons (of cosmic origin) with nitrogen nuclei. On the other hand, the radioactive isotope of carbon– 14C occurs on Earth in the smallest amount. In the nature, there is much less 13C that can be found. The percentages of individual isotopes also vary significantly.Įlemental carbon has three isotopes: 14C, 13C and 12C.
The vast majority of naturally occurring elements have more than one isotope. Isotopes are a set of atoms of the same element that have identical atomic number and different mass number.
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