Thermoluminescence dating problems

Thermoluminescence (TL) dating is a powerful tool in archaeology, and its reliability has been checked since the early s. It is, in principle, specific for.
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Thermoluminescence dating

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You have requested the following content:. If you have an individual subscription to this journal, or if you have purchased this article through Pay-Per-view , you can gain access by logging in with your username and password here: Any other exposure to the minimum amount of heat will reset the accumulated radiation energy Other forms of energy may also cause a release of the stored radiation energy.

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Additional causes for resetting the energy level are: When an item passes through X-ray safety inspection at an airport, or customs inspection at a sea port, the stored energy can be reset or reduced, resulting in an unreliable age test result. Defeating this dating test: Scientific Authentication The problem is Personally I feel uncomfortable with this method of dating.

Like Radiocarbon Dating that has been used for decades in archaeology for dating organic materials, it is based on an axiom. The assumption is that the level of natural radiation has always been the same as it is now. If, however, any major radiation event occurred in the past couple of hundred years, that is, if radiation was not always constant, then the theory is flawed.

Do we know whether it has been constant? As mentioned above, I feel uncomfortable with this.

Methodical problems of thermoluminescence dating of holocene ..|INIS

Ideally this is assessed by measurements made at the precise findspot over a long period. For artworks, it may be sufficient to confirm whether a piece is broadly ancient or modern that is, authentic or a fake , and this may be possible even if a precise date cannot be estimated. Natural crystalline materials contain imperfections: These imperfections lead to local humps and dips in the crystalline material's electric potential.

Where there is a dip a so-called " electron trap" , a free electron may be attracted and trapped. The flux of ionizing radiation—both from cosmic radiation and from natural radioactivity —excites electrons from atoms in the crystal lattice into the conduction band where they can move freely.

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Thermoluminescence dating

Most excited electrons will soon recombine with lattice ions, but some will be trapped, storing part of the energy of the radiation in the form of trapped electric charge Figure 1. Depending on the depth of the traps the energy required to free an electron from them the storage time of trapped electrons will vary as some traps are sufficiently deep to store charge for hundreds of thousands of years. Another important technique in testing samples from a historic or archaeological site is a process known as Thermoluminescence testing.

Which involves a principle that all objects absorb radiation from the environment. This process frees electrons within elements or minerals that remain caught within the item.

Canadian Journal of Earth Sciences

Thermoluminescence testing involves heating a sample until it releases a type of light. This light is then measured to determine the last time the item was heated. When irradiated crystalline material is again heated or exposed to strong light, the trapped electrons are given sufficient energy to escape. In the process of recombining with a lattice ion, they lose energy and emit photons light quanta , detectable in the laboratory. The amount of light produced is proportional to the number of trapped electrons that have been freed which is in turn proportional to the radiation dose accumulated.

In order to relate the signal the thermoluminescence—light produced when the material is heated to the radiation dose that caused it, it is necessary to calibrate the material with known doses of radiation since the density of traps is highly variable. Thermoluminescence dating presupposes a "zeroing" event in the history of the material, either heating in the case of pottery or lava or exposure to sunlight in the case of sediments , that removes the pre-existing trapped electrons.

Therefore, at that point the thermoluminescence signal is zero. As time goes on, the ionizing radiation field around the material causes the trapped electrons to accumulate Figure 2.