A mass spectrometer is used on a small sample to determine the ratio of the isotopic concentrations, which are similar in different regions if the geological time scale is similar.
The method can be used to identify sources of lead impurities in other metals as well as in glass and glaze.
A further use of the method is based on the fact that fission tracks disappear if the substance is heated about 500?
or so: thus a date achieved for clay (like a hearth), pottery, or obsidian that had been burnt gives the date of burning or firing, since previous fission tracks would have disappeared.
SYNONYMS OR RELATED TERMS: stable carbon isotope analysis CATEGORY: technique DEFINITION: A technique for reconstructing past diets (plant foods) by analyzing the isotopic ratios, particularly carbon and nitrogen, contained in human bone.
Human remains are analyzed for a measurement of the ratio between 13C and 12C isotopes in ancient human bone collagen.
SYNONYMS OR RELATED TERMS: oxygen isotope examination CATEGORY: technique DEFINITION: Isotope analysis looking at the O18/O16 ratio in materials.
The method can be used to classify glass types and to analyze mollusk shells in order to try and reconstruct their original environment and thus the source. The basis for this technique is the fact that the ratio of two of the stable isotopes of oxygen varies according to the material in which it is found.
The basis for this technique is that a uranium isotope, U 238, as well as decaying to a stable lead isotope, also undergoes spontaneous fission. Fission is accompanied by an energy release which sends the resulting two nuclei into the surrounding material, the tracks causing damage to the crystal lattice.It can be predicted theoretically and demonstrated experimentally, however, that subtle chemical effects do result from the difference in mass of isotopes.Isotopes of an element may have slightly different equilibrium constants for a particular chemical reaction, so that fractionation of the isotopes results from that reaction.CATEGORY: geology DEFINITION: Atoms of the same element that have different atomic masses due to having different numbers of neutrons in the nuclei, but which still have similar chemical properties.Many of these forms of elements with a specific number of electrons (such as carbon 14 or potassium 40) are unstable and decay into different elements, releasing their surplus electrons.Since the ratio of U 235 to U 238 is known, and is constant, a comparison of the number of tracks from natural fission and the number from induced fission will give the age of the sample.Though the method has been limited in its archaeological use so far, it has already proved a useful check method for for volcanic deposits at Olduvai Gorge, Tanzania, and obsidian, tephra beds, mineral inclusions in pottery, and some man-made glasses have also been dated.Radiocarbon, potassium-argon, fission track, and thermoluminescence dating all rely on this phenomenon in different ways.CATEGORY: technique DEFINITION: A technique based on the relative abundance of lead isotopes, which differ according to the origin of the lead, allowing scientists to pinpoint the source of a piece of lead once the ratios of the isotopes have been determined.The technique is also used to analyze mollusk shells in an attempt to reconstruct the original aquatic environment.Because temperature variations are correlated with changes in atmospheric O18/O16 ratios, oxygen isotope analysis has also been used to identify seasonal changes in SYNONYMS OR RELATED TERMS: radioisotope CATEGORY: term DEFINITION: Any of several species of the same chemical element, such as carbon, with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.