Radiocarbon Dating - Wikipedia, The Free Encyclopedia

Radiocarbon datingFrom Wikipedia, the free encyclopedia

Radiocarbon dating (sometimes simply known as carbon dating) is a radiometric dating method that uses the

naturally occurring radioisotope carbon-14 (14C) to estimate the age of carbon-bearing materials up to about

58,000 to 62,000 years.[1] Raw, i.e., uncalibrated, radiocarbon ages are usually reported in radiocarbon years

"Before Present" (BP), "Present" being defined as 1950. Such raw ages can be calibrated to give calendar dates.One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains fromarchaeological sites. When plants fix atmospheric carbon dioxide (CO

2) into organic material during

photosynthesis they incorporate a quantity of 14C that approximately matches the level of this isotope in theatmosphere (a small difference occurs because of isotope fractionation, but this is corrected after laboratory

analysis[citation needed]). After plants die or they are consumed by other organisms (for example, by humans or

other animals) the 14C fraction of this organic material declines at a fixed exponential rate due to the radioactive

decay of 14C. Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allowsthe age of the sample to be estimated.

The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University ofChicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby ata seminar in Chicago that year. Libby estimated that the steady state radioactivity concentration ofexchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, he was awardedthe Nobel Prize in chemistry for this work. He demonstrated the accuracy of radiocarbon dating by accuratelyestimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian

royal barge of 1850 BC.[2][3]

Contents

1 Physical and chemical background2 Computation of ages and dates3 Methods4 Measurements and scales

4.1 Calibration4.1.1 The need for calibration4.1.2 Calibration methods

5 History6 Carbon exchange reservoir

7 Speleothem studies extend 14C calibration8 Examples9 See also10 References11 Further reading12 External links

Physical and chemical background

Radiocarbon dating - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Radiocarbon_dating

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1: Formation of carbon-14

2: Decay of carbon-14

3: The equation is for living

organisms, and the inequality is for

dead organisms, in which the 14C then

decays (See 2).

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 relatively shorthalf-life of 5,730 years, meaning that the amount of carbon-14 in asample is halved over the course of 5,730 years due to radioactive decay.Carbon-14 would have long ago vanished from Earth were it not for theunremitting cosmic ray flux interactions with the Earth's atmosphere,which create more of the isotope. The neutrons resulting from the cosmicray interactions participate in the following nuclear reaction on theatoms of nitrogen molecules (N

2) in the atmosphere:

The highest rate of carbon-14 production takes place at altitudes of 9 to15 km (30,000 to 50,000 ft), and at high geomagnetic latitudes, but thecarbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide. Carbondioxide also permeates the oceans, dissolving in the water. For approximate analysis it is assumed that thecosmic ray flux is constant over long periods of time; thus carbon-14 is produced at a constant rate and theproportion of radioactive to non-radioactive carbon is constant: ca. 1 part per trillion (600 billion atoms/mole).In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and

locality.[4] For the most accurate work, these variations are compensated by means of calibration curves. Whenthese curves are used, their accuracy and shape are the factors that determine the accuracy of the age obtained

for a given sample.[5] 14C can also be produced at ground level at a rate of 1 x 10−4 g s−1, which is not

considered significant enough to impact on dating without a known other source of neutrons.[6]

Plants take up atmospheric carbon dioxide by photosynthesis, and are ingested by animals, so every living thingis constantly exchanging carbon-14 with its environment as long as it lives. Once it dies, however, this exchangestops, and the amount of carbon-14 gradually decreases through radioactive beta decay with a half-life of 5,730

± 40 years.[7] Carbon-14 is stored in different amounts in different reservoirs because there is a dynamic

equilibrium between 14C production and decay.[6]

Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University ofCalifornia Radiation Laboratory at Berkeley.

Computation of ages and dates

The number of decays per time is proportional to the current number of radioactive atoms. This is expressed bythe following differential equation, where N is the number of radioactive atoms and λ is a positive number calledthe decay constant:

As the solution to this equation, the number of radioactive atoms N can be written as a function of time:

,


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which describes an exponential decay over a timespan t with an initial condition of N0 radioactive atoms at t =

0. Canonically, t is 0 when the decay started. In this case, N0 is the initial number of 14C atoms when the decay

started.

For radiocarbon dating a once living organism, the initial ratio of 14C atoms to the sum of all other carbon atomsat the point of the organism's death and hence the point when the decay started, is approximately the ratio in theatmosphere.

Two characteristic times can be defined:

mean- or average-life: mean or average time each radiocarbon atom spends in a given sample untilit decays.half-life: time lapsed for half the number of radiocarbon atoms in a given sample, to decay,

It can be shown that:

= = radiocarbon mean- or average-life = 8033 years (Libby value)

= = radiocarbon half-life = 5568 years (Libby value)

Notice that dates are customarily given in years BP which implies t(BP) = –t because the time arrow for datesruns in reverse direction from the time arrow for the corresponding ages. From these considerations and theabove equation, it results:

For a raw radiocarbon date:

and for a raw radiocarbon age:

After replacing values, the raw radiocarbon age becomes any of the following equivalent formulae:

using logs base e and the average life:

and

using logs base 2 and the half-life:

Wiggle matching uses the non-linear relationship between the 14C age and calendar age to match the shape of a


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The use of accelerator mass

spectrometers can improve the

sensitivity of radiocarbon dating.

series of closely sequentially spaced 14C dates with the 14C calibration curve.

Methods

Radiocarbon dating of soil organic matter (SOM) is problematic because SOM accumulates from heterogeneous

sources.[8] Fractionation of the heterogeneous organic carbon sources limits the application and interpretation ofcarbon dating of SOM. To remedy the inconsistencies in previous methods of carbon-14 dating of SOM, ahigh-temperature, pyrolysis-combustion technique was used. A combustion system used by the Illinois StateGeological Survey (ISGS), under vacuum, fractions the SOM into a volatile and residual fraction. The volatileresidue contains low-molecular-weight organic compounds, whereas, the residual residue contains high-molecular-weight organic compounds.

Preceding extraction of carbon dioxide from SOM samples, pretreatment is necessary. Each sample must bepretreated with heated 2 N HCl followed by rinsing with deionized water and vacuum filtration. Drying of thesample in a furnace will reduce the accumulation of water within the system.

The combustion system utilized by the ISGS consists of an inner and an outer quartz tube. To ensure pure CO2

production, a vacuum of -25 psi must be established. During volatile pyrolysis, the inner tube is purged withArgon while the outer tube is purged with oxygen. As the oxygen is purged through the outer tube, the volatilecompounds released from the sample are carried by the argon into the outer tube where they are oxidized at 800degree Celsius to form carbon dioxide. The CO

2 and other gases produced from the volatile fraction are then

passed through a cupric oxide furnace and wash traps including 0.5 N AgNO3 solution and a solution of 7.3 g

Na2Cr

2O

7 in 50% H

2SO

4[9] for purification purposes . After the filtration, the CO

2 is then passed through a Dry

Ice-isopropanol trap to trap the water and the CO2 is finally collected in liquid nitrogen traps. The end of the

volatile fraction is marked by the disappearance of the flame in the ignition furnace. Once the purified CO2 is

transferred, the residual pyrolysis begins with the purging of the inner tube with oxygen and outer tube withargon. In pyrolysis of large samples, a stainless steel chamber and a crucible furnace connected to the inner tubeof the combustion system must be used.

The purified CO2 is then converted to benzene for liquid scintillation spectrometry.

Measurements and scales

Measurements are traditionally made by counting the radioactive decayof individual carbon atoms by gas proportional counting or by liquidscintillation counting. For samples of sufficient size (several grams ofcarbon) this method is still widely used in the 2000s. Among others, allthe tree ring samples used for the calibration curves (see below) weredetermined by these counting techniques. Such decay counting,however, is relatively insensitive and subject to large statisticaluncertainties for small samples. When there is little carbon-14 to beginwith, the long radiocarbon half-life means that very few of the carbon-14atoms will decay during the time allotted for their detection, resulting infew disintegrations per minute.

The sensitivity of radiocarbon dating has been greatly increased by the

use of accelerator mass spectrometry (AMS). With this technique 14C atoms can be detected and counted


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directly, as opposed to detecting radioactive decay. Radiocarbon AMS samples are prepared by completelyburning the sample, collecting the resulting carbon dioxide, and reducing it to a solid carbon target for sputtering

atomic carbon ions into the mass spectrometer.[10] This method allows dating samples containing only a fewmilligrams of carbon.

Raw radiocarbon ages (i.e., those not calibrated) are usually reported in "years Before Present" (BP). This is thenumber of radiocarbon years before 1950, based on a nominal (and assumed constant – see "calibration" below)level of carbon-14 in the atmosphere equal to the 1950 level. These raw dates are also based on a slightly-offhistoric value for the radiocarbon half-life. Such value is used for consistency with earlier published dates (see"Radiocarbon half-life" below). See the section on computation for the basis of the calculations.

Radiocarbon dating laboratories generally report an uncertainty for each date. For example, 3000 ± 30 BPindicates a standard deviation of 30 radiocarbon years. Traditionally this included only the statistical countinguncertainty. However, some laboratories supplied an "error multiplier" that could be multiplied by theuncertainty to account for other sources of error in the measuring process. More recently, the laboratories try toquote the overall uncertainty, which is determined from control samples of known age and verified by

international intercomparison exercises.[11] In 2008, a typical uncertainty better than ±40 radiocarbon years canbe expected for samples younger than 10,000 years. This, however, is only a small part of the uncertainty of thefinal age determination (see section Calibration below).

Samples older than the upper age-limit cannot be dated because the small number of remaining intrinsic 14C

atoms will be obscured by 14C background atoms introduced into the samples while they still resided in theenvironment, during sample preparation, or in the detection instrument. As of 2007, the limiting age for a 1

milligram sample of graphite is about ten half-lives, approximately 60,000 years.[12] This age is derived from

that of the calibration blanks used in an analysis, whose 14C content is assumed to be the result of contamination

during processing (as a result of this, some facilities[12] will not report an age greater than 60,000 years for anysample).

A variety of sample processing and instrument-based constraints have been postulated to explain the upperage-limit. To examine instrument-based background activities in the AMS instrument of the W. M. Keck CarbonCycle Accelerator Mass Spectrometry Laboratory of the University of California, a set of natural diamondswere dated. Natural diamond samples from different sources within rock formations with standard geological

ages in excess of 100 Ma yielded14C apparent ages 64,920 ± 430 BP to 80,000 ± 1100 BP as reported in

2007.[13]

Calibration

The need for calibration

Dates may be expressed as either uncalibrated or calibrated years (the latter abbreviated as cal or cal.). A raw

BP date cannot be used directly as a calendar date, because the level of atmospheric 14C has not been strictlyconstant during the span of time that can be radiocarbon dated. The level is affected by variations in the cosmic

ray intensity which is in turn affected by variations in the Earth's magnetosphere.[18] In addition, there aresubstantial reservoirs of carbon in organic matter, the ocean, ocean sediments (see methane hydrate), andsedimentary rocks. Changes in the Earth's climate can affect the carbon flows between these reservoirs and the

atmosphere, leading to changes in the atmosphere's 14C fraction. As the graph to the right shows, there is anoverstatement of the age of the sample of nearly 1000 years in an uncalibrated dating of 7000 BP.


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Calibration curve for the radiocarbon dating scale.

Data sources: Stuiver et al. (1998).[14] Samples with

a real date more recent than AD 1950 are dated

and/or tracked using the N- & S-Hemisphere graphs.

See following figure.

Atmospheric 14C, New Zealand[15] and Austria.[16]

The New Zealand curve is representative for the

Southern Hemisphere, the Austrian curve is

representative for the Northern Hemisphere.

Atmospheric nuclear weapon tests almost doubled

the concentration of 14C in the Northern

Hemisphere.[17]

Aside from these changes due to natural processes, the levelhas also been affected by human activities. From thebeginning of the industrial revolution in the 18th century to

the 1950s, the fractional level of 14C decreased because ofthe admixture of large quantities of CO

2 into the

atmosphere, due to the excavated oil reserves andcombustion production of fossil fuel. This decline is known

as the Suess effect, and also affects the 13C isotope.

However, atmospheric 14C was almost doubled during the

1950s and 1960s due to atmospheric atomic bomb tests.[19]

Calibration methods

The raw radiocarbon dates, in BP years, are calibrated togive calendar dates. Standard calibration curves areavailable, based on comparison of radiocarbon dates ofsamples that can be dated independently by other methodssuch as examination of tree growth rings(dendrochronology), deep ocean sediment cores, lakesediment varves, coral samples, and speleothems (cavedeposits).

The calibration curves can vary significantly from a straightline, so comparison of uncalibrated radiocarbon dates (e.g.,plotting them on a graph or subtracting dates to give elapsedtime) is likely to give misleading results. There are alsosignificant plateaus in the curves, such as the one from11,000 to 10,000 radiocarbon years BP, which is believed tobe associated with changing ocean circulation during theYounger Dryas period. Over the historical period from 0 to10,000 years BP, the average width of the uncertainty ofcalibrated dates was found to be 335 years, although inwell-behaved regions of the calibration curve the widthdecreased to about 113 years while in ill-behaved regions itincreased to a maximum of 801 years. Significantly, in theill-behaved regions of the calibration curve, increasing theprecision of the measurements does not have a significant

effect on increasing the accuracy of the dates.[20]

The 2004 version of the calibration curve extends backquite accurately to 26,000 years BP. Any errors in thecalibration curve do not contribute more than ±16 years to the measurement error during the historic and lateprehistoric periods (0–6,000 yrs BP) and no more than ±163 years over the entire 26,000 years of the curve,

although its shape can reduce the accuracy as mentioned above.[21]

In late 2009, the journal Radiocarbon announced agreement on the INTCAL09 standard, which extends a more

accurate calibration curve to 50,000 years.[22][23]


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History

Carbon dating was developed by American scientist Willard Libby and his team at the University of Chicago.Libby calculated the half-life of carbon-14 as 5568 ± 30 years, a figure now known as the Libby half-life.Following a conference at the University of Cambridge in 1962, a more accurate figure of 5730 ± 40 years wasagreed upon based on more recent experimental data (this figure is now known as the Cambridge half-life).

The chairman of the Cambridge conference, Harry Godwin, wrote to the scientific journal Nature,recommending that the Libby half-life continue to be used for the time being, as the Cambridge figure might

itself be improved by future experiments.[24] Laboratories today continue to use the Libby figure to avoidinconsistencies with earlier publications, although the Cambridge half-life is still the most accurate figure that iswidely known and accepted. However, the inaccuracy of the Libby half-life is not relevant if calibration isapplied: the mathematical term representing the half-life is canceled out as long as the same value is usedthroughout a calculation.

Carbon exchange reservoir

Libby's original exchange reservoir hypothesis assumes that the exchange reservoir is constant all over the

world. The calibration method also assumes that the temporal variation in 14C level is global, such that a small

number of samples from a specific year are sufficient for calibration.[25] However, since Libby's early work waspublished (1950 to 1958), latitudinal and continental variations in the carbon exchange reservoir have been

observed by Hessel de Vries (1958;[4] as reviewed by Lerman et al.[26]). Subsequently, methods have beendeveloped that allow the correction of these so-called reservoir effects, including:

When CO2 is transferred from the atmosphere to the oceans, it initially shares the 14C concentration of

the atmosphere. However, turnaround times of CO2 in the ocean are similar to the half-life of 14C

(making 14C also a dating tool for ocean water).[27] Marine organisms feed on this "old" carbon, and thustheir radiocarbon age reflects the time of CO

2 uptake by the ocean rather than the time of death of the

organism. This marine reservoir effect is partly handled by a special marine calibration curve,[28] but localdeviations of several hundred years exist.

Erosion and immersion of carbonate rocks (which are generally older than 80,000 years and so shouldn't

contain measurable 14C) causes an increase in 12C and 13C in the exchange reservoir, which depends onlocal weather conditions and can vary the ratio of carbon that living organisms incorporate. This isbelieved negligible for the atmosphere and atmosphere-derived carbon since most erosion will flow into

the sea.[29] The atmospheric 14C concentration may differ substantially from the concentration in localwater reservoirs. Eroded from CaCO

3 or organic deposits, old carbon may be assimilated easily and

provide diluted 14C carbon into trophic chains. So the method is less reliable for such materials as well asfor samples derived from animals with such plants in their food chain.

Volcanic eruptions eject large amount of carbon into the air, causing an increase in 12C and 13C in theexchange reservoir and can vary the exchange ratio locally. This explains the often irregular dating

achieved in volcanic areas.[29]

The earth is not affected evenly by cosmic radiation, the magnitude of the radiation depends on land


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altitude and earth's magnetic field strength at any given location, causing minor variation in the local 14Cproduction. This is accounted for by having calibration curves for different locations of the globe.However this could not always be performed, as tree rings for calibration were only recoverable from

certain locations in 1958.[30] The rebuttals by Münnich et al.[4] and by Barker[31] both maintain that

while variations of carbon-14 exist, they are about an order of magnitude smaller than those implied byCrowe's calculations.

These effects were first confirmed when samples of wood from around the world, which all had the same age(based on tree ring analysis), showed deviations from the dendrochronological age. Calibration techniques basedon tree-ring samples have contributed to increased accuracy since 1962, when they were accurate to 700 years

at worst.[32]

Speleothem studies extend 14

C calibration

Speleothems (such as stalagmites) are calcium carbonate deposits that form from drips in limestone caves.

Individual speleothems can be tens of thousands of years old.[33] Scientists are attempting to extend the recordof atmospheric carbon-14 by measuring radiocarbon in speleothems which have been independently dated using

uranium-thorium dating.[34][35] These results are improving the calibration for the radiocarbon technique and

extending its usefulness to 45,000 years into the past.[36] Initial results from a cave in the Bahamas suggested a

peak in the amount of carbon-14 which was twice as high as modern levels.[37] A recent study does not

reproduce this extreme shift and suggests that analytical problems may have produced the anomalous result.[35]

Examples

Ancient footprints of AcahualincaChauvet CaveDolaucothiEve of NaharonHaraldskær WomanKennewick ManShroud of TurinSkeleton LakeThera eruptionVinland map

See also

Arizona Accelerator Mass Spectrometry LaboratoryCarbon sequestrationCosmogenic isotopesDiscussion of half-life and average-life or mean-lifetimeEnvironmental isotopesOld wood

References


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^ Plastino, W.; Kaihola, L.; Bartolomei, P.; Bella, F.(2001). "Cosmic Background Reduction In TheRadiocarbon Measurement By ScintillationSpectrometry At The Underground Laboratory OfGran Sasso"(https://digitalcommons.library.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2Fvolume43%2Fnumber2A%2Fazu_radiocarbon_v43_n2a_157_161_v.pdf) . Radiocarbon 43 (2A): 157–161.https://digitalcommons.library.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2Fvolume43%2Fnumber2A%2Fazu_radiocarbon_v43_n2a_157_161_v.pdf.

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^ Arnold, J. R.; Libby, W. F. (1949). "AgeDeterminations by Radiocarbon Content: Checkswith Samples of Known Age"(http://hbar.phys.msu.ru/gorm/fomenko/libby.htm) .Science 110 (2869): 678–680. Bibcode1949Sci...110..678A (http://adsabs.harvard.edu/abs/1949Sci...110..678A) .doi:10.1126/science.110.2869.678 (http://dx.doi.org/10.1126%2Fscience.110.2869.678) .PMID 15407879 (//www.ncbi.nlm.nih.gov/pubmed/15407879) . http://hbar.phys.msu.ru/gorm/fomenko/libby.htm.

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^ Willard Frank Libby (http://web.archive.org/web/20080208212514/http://www.mnsu.edu/emuseum/information/biography/klmno/libby_willard.html)

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^ a b c Münnich KO, Östlund HG, de Vries H (1958)."Carbon-14 Activity during the past 5,000 Years".Nature 182 (4647): 1432–3. Bibcode1958Natur.182.1432M (http://adsabs.harvard.edu/abs/1958Natur.182.1432M) .doi:10.1038/1821432a0 (http://dx.doi.org/10.1038%2F1821432a0) .

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^ McFadgen, B G et al. (1994). "Radiocarboncalibration curve variations and their implications forthe interpretation of New Zealand prehistory"(http://digitalcommons.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2FVolume36%2FNumber2%2Fazu_radiocarbon_v36_n2_221_236_v.pdf) . Radiocarbon 36 (2): 221–236.http://digitalcommons.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2FVolume36%2FNumber2%2Fazu_radiocarbon_v36_n2_221_236_

v.pdf. "The shape of a distribution of calibrated 14C

dates displays spurious peaks and troughs, brought

about by changes in the slope of the calibration

curve interacting with the spreading effect of the

stochastic distribution of counting errors"

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^ a b Ramsey, C. Bronk (2008). "Radiocarbon dating:revolutions in understanding". Archaeometry 50 (2):249-275. doi:10.1111/j.1475-4754.2008.00394.x(http://dx.doi.org/10.1111%2Fj.1475-4754.2008.00394.x) .

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^ http://hypertextbook.com/facts/1997/MargaretKong.shtml

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^ Wang, Hong; Keith C. Hackley,a Samuel V.Panno,a Dennis D. Coleman,b Jack Chao-li Liu,b andJohnie Brownc (8). "Pyrolysis-combustion 14Cdating of soil organic matter" (http://ac.els-cdn.com/S0033589403001133/1-s2.0-S0033589403001133-main.pdf?_tid=815280222545290bc41a3ae3b164cd90&acdnat=1335240057_f32e355d4e44a37c586151e56a074444) . Quaternary Research 60: 348-355.Bibcode 2003QuRes..60..348W(http://adsabs.harvard.edu/abs/2003QuRes..60..348W) .doi:10.1016/j.yqres.2003.07.004 (http://dx.doi.org/10.1016%2Fj.yqres.2003.07.004) . http://ac.els-cdn.com/S0033589403001133/1-s2.0-S0033589403001133-main.pdf?_tid=815280222545290bc41a3ae3b164cd90&acdnat=1335240057_f32e355d4e44a37c586151e56a074444. Retrieved 04/23/2012.

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^ Coleman, Dennis (1973). "Illinois State GeologicalSurvey Dates IV". Radiocarbon 15 (1): 75-85.

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^ Goslar, T.; Czernik, J. (2000). "Sample Preparationin the Gliwice Radiocarbon Laboratory"(http://www.geochronometria.pl/pdf/geo_18/geo_18_01.pdf) . Geochronmetria 18: 1–8.http://www.geochronometria.pl/pdf/geo_18/geo_18_01.pdf.

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^ Scott, EM (2003). "The Fourth InternationalRadiocarbon Intercomparison (FIRI).". Radiocarbon

45: 135–285.

11.

^ a b "NOSAMS Radiocarbon Data andCalculations" (http://www.nosams.whoi.edu/clients/data.html) . Woods Hole Oceanographic Institution.http://www.nosams.whoi.edu/clients/data.html.

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^ Taylor RE, Southon J (2007). "Use of natural

diamonds to monitor 14C AMS instrumentbackgrounds". Nuclear Instruments and Methods in

Physics Research B 259: 282–28. Bibcode2007NIMPB.259..282T (http://adsabs.harvard.edu/abs/2007NIMPB.259..282T) .doi:10.1016/j.nimb.2007.01.239 (http://dx.doi.org/10.1016%2Fj.nimb.2007.01.239) .

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^ Stuiver M, Reimer PJ, Braziunas TF (1998)."High-precision radiocarbon age calibration forterrestrial and marine samples"(http://depts.washington.edu/qil/datasets

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/uwten98_14c.txt) . Radiocarbon 40: 1127–51.http://depts.washington.edu/qil/datasets/uwten98_14c.txt.

^ "Atmospheric δ14C record from Wellington"(http://cdiac.esd.ornl.gov/trends/co2/welling.html) .Carbon Dioxide Information Analysis Center.http://cdiac.esd.ornl.gov/trends/co2/welling.html.Retrieved 1 May 2008.

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^ "δ14CO2 record from Vermunt"

(http://cdiac.esd.ornl.gov/trends/co2/cent-verm.html). Carbon Dioxide Information Analysis Center.http://cdiac.esd.ornl.gov/trends/co2/cent-verm.html.Retrieved 1 May 2008.

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^ "Radiocarbon dating" (http://www1.phys.uu.nl/ams/Radiocarbon.htm) . Utrecht University.http://www1.phys.uu.nl/ams/Radiocarbon.htm.Retrieved 1 May 2008.

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Physics 224: 423–431. Bibcode2004SoPh..224..423K (http://adsabs.harvard.edu/abs/2004SoPh..224..423K) .doi:10.1007/s11207-005-6498-9 (http://dx.doi.org/10.1007%2Fs11207-005-6498-9) .

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Post-Bomb 14C Data". Radiocarbon 46 (3):1299–1304

19.

^ These results were obtained from a Monte Carloanalysis calibrating simulated measurements ofvarying precision using the 1993 version of thecalibration curve. The width of the uncertaintyrepresents a 2σ uncertainty (that is, a likelihood of95% that the date appears between these limits).Niklaus TR, Bonani G, Suter M, Wölfli W (1994)."Systematic investigation of uncertainties inradiocarbon dating due to fluctuations in thecalibration curve". Nuclear Instruments and

Methods in Physics Research 92: 194–200. Bibcode1994NIMPB..92..194N (http://adsabs.harvard.edu/abs/1994NIMPB..92..194N) .doi:10.1016/0168-583X(94)96004-6(http://dx.doi.org/10.1016%2F0168-583X%2894%2996004-6) .

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^ Reimer Paula J et al. (2004). "INTCAL04Terrestrial Radiocarbon Age Calibration, 0–26 CalKyr BP" (http://digitalcommons.library.arizona.edu/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume46/Number3/azu_radiocarbon_v46_n3_1029_1058_v.pdf) .Radiocarbon 46 (3): 1029–1058.http://digitalcommons.library.arizona.edu/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume46/Number3

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/azu_radiocarbon_v46_n3_1029_1058_v.pdf. A webinterface is here (http://calib.qub.ac.uk/calib/calib.html) .^ Reimer, P.J.; et. al. (2009). "IntCal09 andMarine09 Radiocarbon Age Calibration Curves,0–50,000 Years cal BP"(http://researchcommons.waikato.ac.nz/bitstream/10289/3622/1/Hogg%20Intcal09%20and%20Marine09.pdf) .Radiocarbon 51 (4): 1111–1150.http://researchcommons.waikato.ac.nz/bitstream/10289/3622/1/Hogg%20Intcal09%20and%20Marine09.pdf.

22.

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Further reading

Bowman, Sheridan (1990). Interpreting the Past: Radiocarbon Dating. Berkeley: University of California Press.ISBN 0-520-07037-2.Currie, L. (2004). "The Remarkable Metrological History of Radiocarbon Dating II" (http://nvl.nist.gov/pub/nistpubs/jres/109/2/j92cur.pdf) . J. Res. Natl. Inst. Stand. Technol. 109: 185–217. http://nvl.nist.gov/pub/nistpubs/jres/109/2/j92cur.pdf.Friedrich, M.; et al. (2004). "The 12,460-Year Hohenheim Oak and Pine Tree-Ring Chronology from CentralEurope—a Unique Annual Record for Radiocarbon Calibration and Paleoenvironment Reconstructions".Radiocarbon 46: 1111–1122.Gove, H. E. (1999) From Hiroshima to the Iceman. The Development and Applications of Accelerator MassSpectrometry. Bristol: Institute of Physics Publishing.Kovar, Anton J. (1966). "Problems in Radiocarbon Dating at Teotihuacan". American Antiquity (Society forAmerican Archaeology) 31 (3): 427–430. doi:10.2307/2694748 (http://dx.doi.org/10.2307%2F2694748) .JSTOR 2694748 (//www.jstor.org/stable/2694748) .Lorenz, R. D.; Jull, A. J. T.; Lunine, J. I.; Swindle, T. (2002). "Radiocarbon on Titan". Meteoritics and Planetary

Science 37 (6): 867–874. Bibcode 2002M&PS...37..867L (http://adsabs.harvard.edu/abs/2002M&PS...37..867L) .doi:10.1111/j.1945-5100.2002.tb00861.x (http://dx.doi.org/10.1111%2Fj.1945-5100.2002.tb00861.x) .

Mook, W. G.; van der Plicht, J. (1999). "Reporting 14C activities and concentrations"(http://digitalcommons.library.arizona.edu/index.php/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume41/Number3/azu_radiocarbon_v41_n3_227_239_v.pdf) . Radiocarbon 41: 227–239.http://digitalcommons.library.arizona.edu/index.php/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume41/Number3/azu_radiocarbon_v41_n3_227_239_v.pdf.Weart, S. (2004) The Discovery of Global Warming - Uses of Radiocarbon Dating (http://www.aip.org/history

/climate/Radioc.htm) .Willis, E.H. (1996) Radiocarbon dating in Cambridge: some personal recollections. A Worm's Eye View of the

Early Days (http://www.quaternary.group.cam.ac.uk/history/radiocarbon/) .


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External links

Radiocarbon - The main international journal of record for research articles and date lists relevant to 14C(http://www.radiocarbon.org/)C14dating.com - General information on Radiocarbon dating (http://www.c14dating.com/)calib.org - Calibration program, Marine Reservoir database, and bomb calibration (http://calib.org/)NOSAMS: National Ocean Sciences Accelerator Mass Spectrometry Facility at the Woods HoleOceanographic Institution (http://www.whoi.edu/nosams/page.do?pid=40138.html)Discussion of calibration (http://c14.arch.ox.ac.uk/calibration.html) (from U Oxford)Several calibration programs can be found at www.radiocarbon.org (http://www.radiocarbon.org/Info/index.html)CalPal Online (Cologne Radiocarbon Calibration & Paleoclimate Research Package) (http://www.calpal-online.de)OxCal program (Oxford Calibration) (http://c14.arch.ox.ac.uk/oxcal.html)Fairbanks' Radiocarbon Calibration program (for prior to 12400 BP)(http://radiocarbon.ldeo.columbia.edu/research/radiocarbon.htm)Notes on radiocarbon dating, including movies illustrating the atomic physics (http://id-archserve.ucsb.edu/anth3/courseware/Chronology/08_Radiocarbon_Dating.html) (from UC Santa Barbara)Carbon Dating-How it works? (http://science.howstuffworks.com/environmental/earth/geology/carbon-14.htm,)

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