Alpha efficiency Alpha rays are significantly less effective in producing ESR intensity than beta or gamma rays. The alpha efficiency is the ratio of ESR intensities generated by a given alpha dose over an equivalent beta or gamma dose.
Cosmic rays Ionizing radiation received from space (mainly originating from the sun).
Disequilibrium The activity ratio of two isotopes is different from unity.
Dose Amount of radiation received.
Dose response curve Plot of ESR intensity versus laboratory dose.
Dosimeter An instrument or substance for measuring the dose generated by ionizing radiation (e. g., X-, alpha, beta, gamma and cosmic rays).
Electron spin resonance dating A dating method based on the time dependent, radiation induced accumulation of electrons and holes in the crystal lattice of certain minerals. The age estimate usually refers to the formation of the minerals (e. g., tooth enamel, shells, corals, etc.). The trapped electrons and holes are measured with an electron spin resonance spectrometer. speleothems Carbonate precipitations in caves, consisting of stalactites (growing from the cave ceiling), stalagmites (from the cave floor), and flowstones (sheets). thermoluminescence dating A dating method based on the time dependent, radiation induced accumulation of electrons in the crystal lattice of certain minerals. The age estimate usually
Refers to resetting by light (quartz grains) or heating (pottery, flint). The trapped electrons are measured with a thermoluminescence reader.
Figure 1 Trapping of electrons and holes: the basis for ESR dating. An insulating mineral has two energy levels, at which electrons may occur. The lower energy level (valence band) is separated from the higher energy level (conduction band) by a so-called forbidden zone. When a mineral is formed or reset, all electrons are in the ground state. Ionizing radiation emitted from radioactive elements (U, Th, and K) knocks off negatively charged electrons from atoms. The electrons are transferred to the conduction band and positively charged holes are left behind near the valence band. After a short time of diffusion most of the electrons recombine with the holes. Some electrons can be trapped by impurities (electron traps) in the crystal lattice. These electrons can be directly measured by electron spin resonance spectroscopy. Ea — activation energy or trap depth.
Travertines Carbonate deposits around springs.
U-decay chains There are two naturally occurring U-decay chains. 8U decays via eight alpha emissions to the stable end product 206Pb and 235U via seven alpha emissions to 207Pb. In nature, the atomic 238u/235U ratio is about 138/1.
U-series dating Dating methods based on the time dependent change of the 230Th/234U and 231Pa/235U ratios. When minerals are precipitated from aqueous solutions, they are free of water-insoluble isotopes such as 230Th and 231Pa. With time, 230Th and 231Pa are produced through the radioactive decay of 234U and 235U, respectively. At the time of mineral formation, the 230Th/234U and 231Pa/235U activity ratios are zero, after about
500 000 and 150 000 years, respectively, they approximate equilibrium (i. e., 230Th/234U - 1; 231Pa/235U - 1). This presents the upper dating limits of the methods. 231Pa/235U is only rarely applied because of the shorter dating range and difficulties of precisely measuring 231Pa.
Electron spin resonance (ESR) dating is based on the time-dependent accumulation of electrons and holes in the crystal lattice of certain minerals. The process is the result of the exposure of the mineral to radiation, which is emitted from radioactive isotopes in the sample and its surroundings. In such a way, the mineral acts as a natural dosimeter. A numerical age can be derived from the estimation of the dose a sample has received in the past and the dose rate generated by the already-mentioned radioactive elements. Analysis of tooth enamel is the most common ESR dating application in archaeology. In ideal circumstances, dating of tooth enamel to about one million years seems possible.
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