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Thermoluminescence dating method based on the fact that every material on earth receives a low level of radiation from the radioactive elements in the environment. Many solid materials store small fractions of this energy, which accumulates steadily over time. When the solid material is heated, the stored energy releases and emits light, a phenomenon called thermoluminescence. The age of the sample is assumed to be the length of time since the object was heated to a very high temperature. Thermoluminescence dating has obvious applications for dating volcanic rocks and other geological formations, but it can also be applied to humanly heated objects such as clay vessels, heat-treated stone artifacts, or fired bricks. Samples are taken by crumbling an object such as a potsherd or by drilling any holes in it for core samples. The laboratory সবধsures the natural thermoluminescence of the object রিঃh an alpha radiation counter.
As a rule, trees produce growth rings each year formed by the cambium, or growth layer, lying between the wood and the bark. When the growing season starts, large cells are added to the wood. These cells develop thicker walls and become smaller as the growing season progresses, by the end of the growth season, cell production has ceased altogether. This process occurs every growing year, and a distinct line is formed between the wood of the previous season, with its small cells, and the wood of the next, with its new, large cells.
The thickness of the rings may vary according to the tree's age and annual climatic variations, thick rings are characteristic of good growth years. Weather variations within a circumscribed area tend to run in cycles. A decade of wet years may be followed by five dry decades. One season may break a forty-year rainfall record. These eyeles of climate are reflected in patterns of thicker or thinner tree rings, which are repeated trom tree to tree within a limited area. Dendrochronologists have invented sophisticated methods of correlating rings from different trees so they can build up long master sequences of rings from a number of trunks that may extend over many centuries.
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