DATING METHODS DENDROCHRONOLOGY RADIOCARBON DATING POTASSIUM ARGON DATING LUMINESCENCE DATING ESR DATING FISSION TRACK DATING PROTEIN AND AMINO ACID DIAGENESIS

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<ul><li><p>DATING METHODSDENDROCHRONOLOGY</p><p>RADIOCARBON DATING</p><p>POTASSIUM ARGON DATING</p><p>LUMINESCENCE DATING</p><p>ESR DATING</p><p>FISSION TRACK DATING</p><p>PROTEIN AND AMINO ACID DIAGENESIS DATING</p><p>OBSIDIAN HYDRATIAN DATING</p><p>ARCHEOMAGNETIC DATING</p><p>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</p></li><li><p>TARHLENDRME YNTEMLEROrganik veya inorganik materiyalleri</p><p>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.</p></li><li><p>DENDROCHRONOLOGY</p><p>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.</p><p>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. </p></li><li><p>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.</p><p>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. </p><p>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 </p><p>on bone or charcoal, </p><p>as these are the organics that most frequently survive from the past, but many other materials can also be dated using this technique. </p></li><li><p>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. </p></li><li><p>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)</p></li><li><p>POTASSIUM ARGON DATINGPotassium-Argon Dating </p><p>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. </p></li><li><p>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</p></li><li><p>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)</p></li><li><p>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.</p><p>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.</p></li><li><p>LUMINESCENCE DATINGAs far as dating is concerned, the phenomenon of luminescence can be subdivided according to the kind of energy supply during stimulation into</p><p> thermoluminescence (TL, stimulated by heat) </p><p> optical stimulated luminescence (OSL, stimulated by visible light) </p><p> infrared stimulated luminescence (IRSL, stimulated by infrared light) </p><p>ELSEC 9010 osl device</p></li><li><p>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.</p></li><li><p>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.</p><p>The two types of luminescence are distinguished by the atomic mechanisms whereby the light is emitted.</p></li><li><p>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)</p></li><li><p>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. How-ever, it is not clear that the same defect centres are involved in both processesin any one material (McKeever, 2001). OSL has several advantages over TL.When dealing with unheated materials (i.e. materials zeroed by light ex-posure) the most important of these advantages are that in OSL only thetrapping levels most sensitive to light are sampled; that is the charge popula-tion most eectively zeroed. In many samples, it is believed that 99% of theinitial OSL signal originates from the 325 C TL peak in quartz (Murray andWintle, 1999). Another advantage of OSL over TL is that stimulation can beperformed at room temperature (although some advantages may be obtainedat slightly elevated temperatures), which means that thermal quenching isnot made worse by heating.</p></li><li><p>Trap mechanismTrap mechanism, namely the time-dependent accumulation of electrons and holes in the crystal lattice of certain common minerals (trap). The minerals are acting as natural radiation dosimeters. When a mineral is formed or reset, all electrons are in the ground state. Naturally occurring radioactive isotopes (U, Th, and K) emit a variety of rays which ionize atoms. Negatively charged electrons are knocked off atoms in the ground state (valence band) and transferred to a higher energy state (conduction band); positively charged holes remain near the valence band. Trap schematicThe trapped electrons and holes forms luminescence centres which can be stimulated. For the measurement of a luminescence signal, the trapped electrons have to be either thermally (by heating) or optically (by light exposure) activated. The electrons return to the conduction band and most of them will recombine with the holes. If such holes are luminescence centres, light emission (luminescence) is observed. </p></li><li><p>Zeroing a trapFigure show the basic principles of the dating process. A zeroing event resets any previously stored trapped electrons - this resetting may be heating, exposure to sunlight or mineral formation. After zeroing, new electrons and holes are trapped as a result of natural radiation </p></li><li><p>ReferencesChronometric Dating in Archaelogy (Edited by R.E.Taylor and Martin j.Aitken)Archaeological dating using physical phenomena(M.J. Aitken)</p></li><li><p>Electron spin resonance</p></li><li><p>ESR DATING Electron spin resonance (ESR) was proposed as a dating method by Zeller as early as 1967, but its practical application began with the work of Ikeya in 1975.Study based on carbonate materials, bones, and quartz ESR-dating is a powerful tool to date the time of mineralization, sedimentation or last heating of minerals. The dating method has the same dosimetric basis as TL/OSL, but in contrast to these methods only paramagnetic centers are detected with ESR. As the measurement does not destroy the centers however, it can be repeated several times. Figure 1: Created by ionising radiation, point defects accumulate predictably in enamel. Imperfections in the crystal lattice exist between the valence and conduction bands, trapping free radicals </p></li><li><p>FISSION TRACK DATINGFission track dating is a radiometric dating technique based on analyses of the damage trails, or tracks, left by fission fragments in certain uranium bearing minerals and glasses. </p><p>Uranium-238 undergoes spontaneous fission decay at a known rate. The fragments emitted by this fission process leave trails of damage in the crystal structure of the minerals enclosing the uranium Fission tracks in an apatite crystal (top) and in a muscovite mica (bottom). </p></li><li><p>FISSION TRACK DATINGEtching of polished surfaces of these minerals reveals the spontaneous fission tracks for counting by optical microscopic means. The number of tracks correlates directly with the age of the sample and the uranium content Fission Tracks (FT) are micrometer-sized, linear damage tracks that occur in insulating minerals and that are caused by the spontaneous fission of heavy, unstable nuclides (mostly 238U in natural minerals). The spontaneous fission of 238U occurs at a specific rate, described by the decay constant (l f = 8.46 10-17a-1). This implies that when the uranium concentration (CU) of a sample is known, the spontaneous FT density (r s = number of tracks/cm2) in that sample is an indication for the samples age. r s is determined by counting the tracks under an optical microscope (at 1250 magnification). Since FTs are features at an atomic scale, they require chemical techniques (etching) to make them observable under the optical microscope. CU is measured by irradiating the sample in a nuclear reactor with thermal neutrons </p></li><li><p>PROTEIN AND AMINO ACID DIAGENESIS DATINGAt a widely publicized news conference in August of 1972, Dr. Jeffrey Bada of Scripps Institute of Oceanography announced the "discovery" of a new dating method based on the rate of racemization of amino acids in fossil material. He was quoted as saying that he had discovered the basis of the method in 1968, and that it was so obvious and simple he was amazed it hadn't been discovered earlier. Amino acids are the "building blocks," or sub-units, of proteins. About 20 different kinds of amino acids are found in proteins. All amino acids in proteins (except glycine) are L-amino acids. These amino acids spontaneously tend to slowly change to the D-form. The D-form tends to revert to the L-form, and eventually an equilibrium is obtained, as illustra...</p></li></ul>

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