DATING METHODS DENDROCHRONOLOGY RADIOCARBON DATING POTASSIUM ARGON DATING LUMINESCENCE DATING ESR...
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POTASSIUM ARGON DATING
FISSION TRACK DATING
PROTEIN AND AMINO ACID DIAGENESIS DATING
OBSIDIAN HYDRATIAN DATING
SURFACE DATING USING ROCK VANISHOne of the most important questions asked about any ancient object is just how old it really is.There are a number of scientific techniques which can be used to date antiquities
TARHLENDRME YNTEMLEROrganik veya inorganik materiyalleri
Radyokarbon (C-14), Dendrokronoloji-Tree ring dating, Elektron Spin Rezonans (ESR),Termolminesans (TL) ve OSL gibi arkeometrinin en nemli uygulamalar arasnda saylabilecek yntemlerle tarihlendirmek mmkndr.Potasyum Argon Metodu (KA): Radyoaktif olan (potasyumun) radyoaktif olmayan Argon40 gazna dnmesine dayanr. zellikle jeolojik tabakalar iinde bulunan fosil kalntlarna uygulanr. 100.000 yl akn volkanik kayalara da uygulanmaktadr.Radyokarbon Metodu (C-14): 1955' te Amerika'da Chicago niversitesi'nde W. Libby ve arkadalar bu metodu uygulamlardr. Bu tarihten itibaren en geerli, en yaygn tarihlendirme metodudur. zellikle tarih ncesi arkeolojide kullanlr. Tm organik maddelerde bulunan radyoaktif karbonun, bunlarn canllklarn kaybetmelerinden sonra belirli bir tempoda azald gzlenmitir. Bu oran bilindiinden, bulunan organic maddenin ya, bu gznnde tutularak bulunur. llere gre yaklak olarak organik maddelerin mrlerinin yars boyunca ylda 5568 karbon kaybettikleri anlalmtr. Sakncal yan tam doru netice vermemesidir.Nedeni de atmosferin her zaman ayn miktarda karbon ihtiva etmemesidir.Dendrokronoloji: Amerikal A.E. Douglass tarafndan bulunan, aa gvdelerinin enine kesitinde grlen yllk halka tabakalarnn incelenmesine dayanan tarihlendirme yntemidir. Aalar her yl gvdesinde yeni bir halka oluturur. Bu halka bol yal yllarda kaln, az yal yllarda ince olur. Douglass eski evlerde kullanlan aalardan zel bir teknikle kesit alarak, zerlerindeki halkalar sayp yaplarn tarihini saptamay baarmtr.Termolminesans Metodu: Ta, keramik, cam gibi kristal yapya sahip maddelerin ya tayininde kullanlr.
Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree-ring growth patterns. This technique was invented and developed during the 20th century originally by A. E. Douglass,the founder of the Laboratory of Tree-Ring Research at the University of Arizona. The technique can date wood to exact calendar years.
Visible rings result from the change in growth speed through the seasons of the year, thus one ring usually marks the passage of one year in the life of the tree.
Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope isotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 yearsThe technique of radiocarbon dating was discovered by Willard Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago.
Probably the best known and most frequently used is radiocarbon or 14C dating. Radiocarbon dating can only be applied to organisms that were once alive and is a means of determining how long ago they died. Radiocarbon dating is possible because of the existence in nature of a tiny amount of 14C, or radiocarbon, a radioactive isotope of carbon.
By measuring how much 14C remains in ancient organic materials, it is possible to calculate how long ago they died. To do this requires extensive chemical processing, carried out in laboratoriesTo convert the carbon in the ancient objects to a form in which the very low level radioactivity can be measured. Most radiocarbon dating is carried out
on bone or charcoal,
as these are the organics that most frequently survive from the past, but many other materials can also be dated using this technique.
RADIOCARBON DATING Carbon has two stable, nonradioactive isotopes : carbon-12 (12C), and carbon-13 (13C). In addition, there are trace amounts of the unstable isotope carbon-14(14C) on Earth. Carbon-14 has a half-life of 5730 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which create more of the isotope.
This 14C isotope is produced in the upper atmosphere by the action of cosmic rays on 14N. This 14C combines with oxygen to produce carbon dioxide (CO2) and is taken in by plants during photosynthesis. From plants this 14C is absorbed into the tissues of every living thing via the food chain. Since it is radioactive, it is unstable and decays away at a known rate. While any plant or animal is alive the 14C lost by radioactive decay is constantly replaced through the food chain, but when that organism dies,no more 14C is taken in, and the amount present in the tissues goes down. (from Aitken 1990)
POTASSIUM ARGON DATINGPotassium-Argon Dating
is the only technique for dating very old archaeological materials. Geologists have used this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, Potassium-40 (K-40) ,decays to the gas Argon as Argon-40 (Ar-40). By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined.
In principle all the materials containing quartz or feldspars and submitted to heating to several hundreds of degrees centigrate can be dated by this way
LUMINESCENCE DATING Materials with suitable luminescence properties can be dated because at some point in the past traps are emptied of their charge by sufficient exposure to heat or light. Subsequently, traps become refilled because of continued ionization by radioactivity and a latent luminescence signal steadily accumulates Optical dating is method of determining how long ago minerals were last exposed to daylight, It is useful to geologists and archaeologists who want to know when such an event occurred. Time clock become zero for a sediment of earthquake line,or sediment of loess.Thermo luminescence dating is method of determining how long ago minerals heated to 800-1000C degrees; then when heated time clock become zero (for making pottery or baked brick)
In phosphorescence the energy difference between the excited state and themeta stable state is generally so small that detrapping occurs by lattice vibra-tions at ambient temperature, i.e. no external supply of energy is required.
However, in TL and OSL the energy difference between the excited stateand the meta stable state is so large that external energy must be appliedto detrap the electrons. In TL the luminescence emission is accelerated bythermal stimulation whereas in OSL the luminescence emission is accelerated by optical stimulation.
LUMINESCENCE DATINGAs far as dating is concerned, the phenomenon of luminescence can be subdivided according to the kind of energy supply during stimulation into
thermoluminescence (TL, stimulated by heat)
optical stimulated luminescence (OSL, stimulated by visible light)
infrared stimulated luminescence (IRSL, stimulated by infrared light)
ELSEC 9010 osl device
Basic Concepts in LuminescenceLuminescence is a generic term for the electromagnetic radiation (usually in the form of visible light) emitted as a consequence of an atomic or molecular non-thermal excitation. Thus, luminescence is often described as cold light to distinguish it from incandescent light emission, which occurs when a material is excited thermally. Luminescent materials are able to absorb energy, store part of it and convert it into light; these materials usually have a crystalline structure.
Luminescence can broadly be categorised as either Fluorescence or phospho-rescence. Fluorescence: the light emission resulting from the relaxation of an electron from an excited state to the ground state (possibly through a metastable state from which transition to the ground state is allowed). The delay between the absorption of energy resulting in the excited state and the emission is determined by the life time of the excited state.The life time can be as short as picoseconds and as long as milliseconds in special cases. Photoluminescence, cathodo luminescence, chemi-luminescence, bioluminescence and triboluminescence are all examples of different fluorescence processes with different means of excitation(i.e. photons, electrons, chemical energy, biochemical and mechanical energy, respectively)Phosphorescence: the relaxation back to the ground state is delayed by a relaxation to the ground state is not permitted. These meta stable states function as electron traps, and energy must be supplied to detrap (release) the electrons back to the excited state from where they can relax to the ground state (McKinlay, 1981). The return to the ground state is thus delayed for period of time; the length of which depends on the life time of the electron in the meta stable state.
The two types of luminescence are distinguished by the atomic mechanisms whereby the light is emitted.
How stimulation occurs With optical dating,the signal is obtained by exposure to a beam of blue /green light or infrared radiation. Optically-stimulated luminescence(OSL) is commonly used , also it is calling as Photon stimulated luminescence (PSL) and Photoluminescence(PL)
Optically stimulated luminescence relies on the same basic concepts as TL,but in OSL the stimulation energy is supplied by photons instead of heat.Thus, the physical principles of OSL are closely related to those of TL