Radiocarbon dating
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'''Radiocarbon dating''' is a [[radiometric dating]] method that uses the naturally occurring [[radioisotope]] [[carbon-14]] (<sup>14</sup>C) to determine the age of [[carbonaceous]] materials up to about 60,000 years.<ref>{{cite journal |last=Plastino |first=W. |authorlink= |coauthors=Kaihola, L.; Bartolomei, P.; Bella, F. |year=2001 |month= |title=Cosmic Background Reduction In The Radiocarbon Measurement By Scintillation Spectrometry At The Underground Laboratory Of Gran Sasso |journal=Radiocarbon |volume=43 |issue=2A |pages=157–161 |id= |url=https://digitalcommons.library.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2Fvolume43%2Fnumber2A%2Fazu_radiocarbon_v43_n2a_157_161_v.pdf |accessdate= |quote= }}</ref> Raw, i.e. uncalibrated, radiocarbon ages are usually reported in '''radiocarbon years''' "[[Before Present]]" (BP), "Present" being defined as [[AD]] 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 from archaeological sites. When plants fix atmospheric [[carbon dioxide]] ({{co2}}) into organic material during [[photosynthesis]] they incorporate a quantity of <sup>14</sup>C that approximately matches the level of this isotope in the atmosphere (a small difference occurs because of [[isotope fractionation]], but this is corrected after laboratory analysis). After plants die or they are consumed by other organisms (for example, by humans or other animals) the <sup>14</sup>C fraction of this organic material declines at a fixed [[exponential decay|exponential rate]] due to the [[Beta decay|radioactive decay]] of <sup>14</sup>C. <!-- (this assumes that the organic material persists; most is [[cellular respiration|respired]] back to {{co2}}).--> Comparing the remaining <sup>14</sup>C fraction of a sample to that expected from atmospheric <sup>14</sup>C allows the age of the sample to be estimated.
The technique of radiocarbon dating was developed by [[Willard Libby]] and his colleagues at the [[University of Chicago]] in 1949.<ref name=libby49>{{cite journal |last=Arnold |first=J. R. |authorlink= |coauthors=Libby, W. F. |year=1949 |month= |title=Age Determinations by Radiocarbon Content: Checks with Samples of Known Age |journal=[[Science (journal)|Science]] |volume=110 |issue=2869 |pages=678–680 |doi=10.1126/science.110.2869.678 |url=http://hbar.phys.msu.ru/gorm/fomenko/libby.htm |accessdate= |quote=|pmid=15407879 }}</ref> Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, he was awarded the [[Nobel Prize in chemistry]] for this work. He first demonstrated the accuracy of radiocarbon dating by accurately measuring the age of wood from an [[ancient Egypt]]ian royal barge whose age was known from historical documents.<ref name=libby49/>
==Basic physics==
[[Image:Radiocarbon bomb spike.svg|thumb|300px|right|Atmospheric <sup>14</sup>C, [[New Zealand]]<ref>[http://cdiac.esd.ornl.gov/trends/co2/welling.htm Atmospheric δ<sup>14</sup>C record from Wellington], [[Carbon Dioxide Information Analysis Center]]. Retrieved [[1 May]] [[2008]].</ref> and [[Austria]]<ref>[http://cdiac.esd.ornl.gov/trends/co2/cent-verm.htm δ<sup>14</sup>{{co2}} record from Vermunt], [[Carbon Dioxide Information Analysis Center]]. Retrieved [[1 May]] [[2008]].</ref>. 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 <sup>14</sup>C in the Northern Hemisphere<ref>[http://www1.phys.uu.nl/ams/Radiocarbon.htm Radiocarbon dating], [[Utrecht University]]. Retrieved [[1 May]] [[2008]].</ref>.]]
[[Carbon]] has two stable, nonradioactive [[isotope]]s: [[carbon-12]] (<sup>12</sup>C), and [[carbon-13]] (<sup>13</sup>C). In addition, there are trace amounts of the unstable isotope [[carbon-14]] (<sup>14</sup>C) 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. The [[neutron]]s resulting from the cosmic ray interactions participate in the following [[nuclear reaction]] on the atoms of nitrogen molecules (N<sub>2</sub>) in the atmospheric air:
:<math>n + \mathrm{~^{14}_{7}N}\rightarrow\mathrm{~^{14}_{6}C}+ p</math>
The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km (30,000 to 50,000 ft), and at high [[geomagnetic]] latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with [[oxygen]] to form [[carbon dioxide]]. Carbon dioxide also permeates the [[ocean]]s, dissolving in the water. For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 is produced at a constant rate and the proportion of radioactive to non-radioactive carbon is constant: ca. 1 [[parts per trillion|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. For the most accurate work, these variations are compensated by means of [[calibration curve]]s. When these curves are used, their accuracy and shape are the factors that determine the accuracy and age obtained for a given sample.
Plants take up atmospheric carbon dioxide by [[photosynthesis]], and are ingested by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. Once it dies, however, this exchange stops, and the amount of carbon-14 gradually decreases through radioactive [[beta decay]].
:<math>\mathrm{~^{14}_{6}C}\rightarrow\mathrm{~^{14}_{7}N}+ e^- + \bar{\nu}_e</math>
<!--
<sup>14</sup>C behaves slightly <sup>12</sup>C and <sup>13</sup>C (due to different atomic mass), such that the isotopes will be involved in reactions out of ratio <ref>{{cite book |title=Physics and Archaeology |last=Aitken |first=M. J. |authorlink= |coauthors= |year=1961 |publisher=Interscience Publishers |location=New York |isbn= |pages= }}</ref>. This so called "fractionation" can however be reliable corrected with the assumption that the fractionation of 14C and 12C is twice the fractionation of the stable isotopes 13C and 12C.
-->
==Computation of ages and dates==
The radioactive decay of carbon-14 follows an [[exponential decay]].
A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. Symbolically, this can be expressed as the following [[differential equation]], where ''N'' is the quantity and λ is a positive number called the '''decay constant''':
:<math>\frac{dN}{dt} = -\lambda N.</math>
The solution to this equation is:
:<math>N = N_0e^{-\lambda t}\,</math>,
where, for a given sample of carbonaceous matter:
:<math>N_0</math> = number of radiocarbon atoms at <math>t = 0</math>, i.e. the origin of the ''disintegration time'',
:<math>N</math> = number of radiocarbon atoms remaining after radioactive decay during the ''time'' <math>t</math>,
:<math>{\lambda}</math> = radiocarbon decay or ''disintegration constant''.
Two related ''times'' can be defined:
:* mean- or average-life: mean or average time each radiocarbon atom spends in a given sample until it decays.
:* half-life: time lapsed for half the number of radiocarbon atoms in a given sample, to decay,
It can be shown that:
:<math>t_{avg} \,</math> = <math> \frac{1}{\lambda} </math> = radiocarbon mean- or average-life = 8033 years (Libby value)
:<math>t_\frac{1}{2} \,</math> = <math> t_{avg} \cdot \ln 2 </math> = 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
dates runs in reverse direction from the time arrow for the corresponding ages. From these considerations and the above equation, it results:
For a raw radiocarbon date:
:<math>t(BP) = \frac{1}{\lambda} {\ln \frac{N}{N_0}}</math>
and for a raw radiocarbon age:
:<math>t(BP) = -\frac{1}{\lambda} {\ln \frac{N}{N_0}}</math>
After replacing values, the raw radiocarbon age becomes any of the following equivalent formulae:
using logs base ''e'' and the average life:
:<math>t(BP) = -t_{avg}\cdot \ln{\frac{N}{N_0}}</math>
and
using logs base ''2'' and the half-life:
:<math>t(BP) = -t_\frac{1}{2}\cdot \log_2 \frac{N}{N_0}</math>
==Measurements and scales==
Measurements are traditionally made by counting the [[radioactive decay]] of individual carbon [[atom]]s by gas [[Proportional counter|proportional counting]] or by [[liquid scintillation counting]]. For samples of sufficient size (several grams of carbon) this method is still widely used in the 2000s. Among others, all the tree ring samples used for the calibration curves (see below) were determined by these counting techniques. Such decay counting, however, is relatively insensitive and subject to large statistical uncertainties for small samples. When there is little carbon-14 to begin with, the long radiocarbon [[half-life]] means that very few of the carbon-14 atoms will decay during the time allotted for their detection, resulting in few disintegrations per minute.
The sensitivity of the method has been greatly increased by the use of [[Accelerator Mass Spectrometry]] (AMS). With this technique <sup>14</sup>C atoms can be detected and counted directly ''vs'' only detecting those atoms that decay during the time interval allotted for an analysis. AMS allows dating samples containing only a few milligrams of carbon.
Raw radiocarbon ages (i.e., those not calibrated) are usually reported in "years [[Before Present]]" (BP). This is the number of radiocarbon years before 1950, based on a nominal (and assumed constant - see "[[Radiocarbon dating#Calibration|calibration]]" below) level of carbon-14 in the atmosphere equal to the 1950 level. These raw dates are also based on a slightly-off historic value for the radiocarbon half-life. Such value is used for consistency with earlier published dates (see "[[Radiocarbon dating#Radiocarbon half-life|Radiocarbon half-life]]" below). See the section on [[#Computation of ages and dates|computation]] for the basis of the calculations.
Radiocarbon dating laboratories generally report an uncertainty for
each date. For example, 3000±30BP indicates a [[standard deviation]] of 30 radiocarbon years. Traditionally this included only the statistical counting uncertainty. However, some laboratories supplied an "error multiplier" that could be multiplied by the uncertainty to account for other sources of error in the measuring process. More recently, the laboratories try to quote the overall uncertainty, which is determined from control samples of known age and verified by international intercomparison exercises <ref>{{cite journal|title=The Fourth International Radiocarbon Intercomparison (FIRI).
Radiocarbon|last=Scott|first=E. M.|journal=Radiocarbon|volume=45|pages=135–285|year=2003)}}</ref>. In 2008, a typical uncertainty better than ±40 radiocarbon years can be expected for samples younger than 10,000 years. This, however, is only a small part of the uncertainty of the final age determination (see section [[Radiocarbon dating#Radiocarbon half-life|Calibration]] below).
[[As of 2007]], the limiting age for a 1 milligram sample of graphite is about ten half-lives, approximately 60,000 years<ref name=nosams>"[http://www.nosams.whoi.edu/clients/data.html NOSAMS Radiocarbon Data and Calculations]", [[Woods Hole Oceanographic Institution]]</ref>. This age is derived from that of the [[calibration]] blanks used in an analysis, whose <sup>14</sup>C content is assumed to be the result of contamination during processing (as a result of this, some facilities<ref name=nosams/> will not report an age greater than 60,000 years for any sample).
A variety of sample processing and instrument-based constraints have been postulated to explain the upper age-limit. To examine instrument-based background activities in the AMS instrument of the W. M. Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory of the University of California, a set of natural diamonds were dated. Natural diamond samples from different sources within rock formations with standard geological ages in excess of 100 my yielded <sup>14</sup>C apparent ages 64,920±430 BP to 80,000±1100 BP as reported in 2007<ref>{{cite journal | title=Use of natural diamonds to monitor <sup>14</sup>C AMS instrument backgrounds | last=Taylor | first=R.E.| coauthors=Southon, J. | journal=Nuclear Instruments and Methods in Physics Research B | volume=259 | pages=282–287 | year=2007 | doi=10.1016/j.nimb.2007.01.239}}</ref>.<!-- THE FOLLOWING STATEMENT IS FROM THE CITED WORK'S INTRO SECTION (NOT RESULTS/DISCUSSION) AND MAY BE OUT OF CONTEXT HERE: In contrast to the sample processing and instrument-based background theories, the authors of an AMS instrument background study conclude: "<sup>14</sup>C from the actual sample is probably the dominant component of the 'routine' background". -->
=== Calibration ===
====The need for calibration====
[[Image:radiocarbon dating calibration.svg|thumb|300px|right| Calibration curve for the radiocarbon dating scale. Data sources: Stuiver ''et al.'' (1998)<ref>{{cite journal |last=Stuiver |first=M. |authorlink= |coauthors=Reimer, P. J.; Braziunas, T. F. |year=1998 |month= |title=High-Precision Radiocarbon Age Calibration for Terrestrial and Marine Samples |journal=Radiocarbon |volume=40 |issue= |pages=1127–1151 |id= |url=http://depts.washington.edu/qil/datasets/uwten98_14c.txt |accessdate= |quote= }}</ref>. Samples with a real date more recent than AD 1950 are dated and/or tracked using the N- & S-Hemisphere graphs. See preceding figure.]]
A raw BP date cannot be used directly as a calendar date, because the level of atmospheric <sup>14</sup>C has not been strictly constant during the span of time that can be radiocarbon dated. The level is affected by variations in the [[cosmic ray]] intensity which is affected by variations in the earth's magnetosphere. In addition there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments (see [[methane hydrate]]), and [[sedimentary rock]]s. Changing [[climate]] can sometimes disrupt the carbon flow between these reservoirs and the atmosphere. The level has also been affected by human activities—it was almost doubled for a short period due to [[atomic bomb]] tests in the 1950s and 1960s and has been lowered by the admixture of large amounts of CO<sub>2</sub> from ancient organic sources relatively depleted in <sup>14</sup>C —the combustion products of [[fossil fuel]]s used in industry and transportation, known as the [[Suess effect]].
====Calibration methods====
The raw radiocarbon dates, in BP years, are calibrated to give calendar dates. Standard [[calibration curve]]s are available, based on comparison of radiocarbon dates of samples that can be dated independently by other methods such as examination of tree growth rings ([[dendrochronology]]), deep ocean [[sediment]] cores, lake sediment [[varve]]s, [[coral]] samples, and [[speleothem]]s (cave deposits).
The calibration curves can vary significantly from a straight line, so comparison of uncalibrated radiocarbon dates (e.g., plotting them on a graph or subtracting dates to give elapsed time) is likely to give misleading results. There are also significant plateaus in the curves, such as the one from 11,000 to 10,000 radiocarbon years BP, which is believed to be associated with changing ocean circulation during the [[Younger Dryas]] period. Over the historical period from 0 to 10,000 years BP, the average width of the uncertainty of calibrated dates was found to be 335 years, although in well-behaved regions of the calibration curve the width decreased to about 113 years while in ill-behaved regions it increased to a maximum of 801 years. Significantly, in the ill-behaved regions of the calibration curve, increasing the precision of the measurements does not have a significant effect on increasing the accuracy of the dates.<ref>These results were obtained from a [[Monte Carlo method|Monte Carlo]] analysis calibrating simulated measurements of varying precision using the 1993 version of the calibration curve. The width of the uncertainty represents a 2σ uncertainty (that is, a likelihood of 95% that the date appears between these limits). T. R. Niklaus, G. Bonani, M. Suter, and W. Wölfli, "Systematic investigation of uncertainties in radiocarbon dating due to fluctuations in the calibration curve." ''Nuclear Instruments and Methods in Physics Research'' B 92 (1994): 194-200.</ref>
The 2004 version of the calibration curve extends back quite accurately to 26,000 years BP. Any errors in the calibration curve do not contribute more than ±16 years to the measurement error during the historic and late prehistoric 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.<ref>{{cite journal |last=Reimer |first=Paula J. |authorlink= |coauthors=''et al.'' |year=2004 |month= |title=INTCAL04 Terrestrial Radiocarbon Age Calibration, 0–26 Cal Kyr BP |journal=Radiocarbon |volume=46 |issue= |pages=1029–1058 |id= |url=http://digitalcommons.library.arizona.edu/index.php/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume46/Number3/azu_radiocarbon_v46_n3_1029_1058_v.pdf |accessdate= |quote= }}</ref>
==Radiocarbon half-life==
=== Libby vs Cambridge values ===
Carbon dating was developed by a team led by [[Willard Libby]]. Originally a carbon-14 half-life of 5568±30 years was used, which is now known as the Libby half-life. Later a more accurate figure of 5730±40 years was determined, which is known as the Cambridge half-life. This is, however, not relevant for radiocarbon dating. If calibration is applied, the half-life cancels out, as long as the same value is used throughout the calculations. Laboratories continue to use the Libby figure to avoid inconsistencies with previous publications.
== 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 <sup>14</sup>C level is global, such that a small number of samples from a specific year are sufficient for calibration.<ref>{{cite book |title=Radiocarbon dating |last=Libby |first=W. F. |authorlink= |coauthors= |year=1955 |publisher=University of Chicago Press |location=Chicago |isbn= |edition=2nd edition }}</ref> However, since Libby's early work was published (1950 to 1958), latitudinal and continental variations in the carbon exchange reservoir have been observed by [[Hessel de Vries]] (1958; as reviewed by Lerman ''et al.'', 1959, 1960). Subsequently, methods have been developed that allow the correction of these so-called ''reservoir effects'', including:
* When CO<sub>2</sub> is transferred from the atmosphere to the oceans, it initially shares the <sup>14</sup>C concentration of the atmosphere. However, turnaround times of CO<sub>2</sub> in the ocean are similar to the half-life of <sup>14</sup>C (making <sup>14</sup>C also a dating tool for ocean water<ref>A. P. McNichol, R. J. Schneider, K. F. von Reden, A. R. Gagnon, K. L. Elder, NOSAMS, R. M. Key, P. D. Quay, Ten years after - The WOCE AMS radiocarbon program, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Volume 172, Issues 1-4, October 2000, Pages 479-484.
(http://www.sciencedirect.com/science/article/B6TJN-41MHFHC-2Y/1/d7be7f3719c79ac70a3ab99ca1bc97c6)</ref>). Marine organisms feed on this "old" carbon, and thus their radiocarbon age reflects the time of CO<sub>2</sub> 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 <ref>M. Stuiver and T.F. Braziunas, Modelling atmospheric <sup>14</sup>C influences and <sup>14</sup>C ages of marine samples to 10,000 BC, Radiocarbon 35 (1993) (1), p. 137</ref>, but local deviation of several 100 years exist.
* Erosion and immersion of carbonate rocks (which are generally older than 80,000 years and so shouldn't contain measurable <sup>14</sup>C) causes an increase in <sup>12</sup>C and <sup>13</sup>C in the exchange reservoir, which depends on local weather conditions and can vary the ratio of carbon that living organisms incorporate. This is believed negligible for the atmosphere and atmosphere-derived carbon since most erosion will flow into the sea.<ref name="Kolchin1972">{{cite book |title=Absolute Archaeological Datings and their Problems |last=Kolchin |first=B. A. |authorlink= |coauthors=Shez, Y. A. |year=1972 |publisher=Nauka |location=Moscow |isbn= |pages= }}</ref>. The atmospheric <sup>14</sup>C concentration may differ substantially from the concentration in local water reservoirs. Eroded from CaCO<sub>3</sub> or organic deposits, old carbon may be assimilated easily and provide diluted <sup>14</sup>C carbon into trophic chains. So the method is less reliable for such materials as well as for samples derived from animals with such plants in their food chain.
* Volcanic eruptions eject large amount of carbonate into the air, causing an increase in <sup>12</sup>C and <sup>13</sup>C in the exchange reservoir and can vary the exchange ratio locally. This explains the often irregular dating achieved in volcanic areas.<ref name="Kolchin1972" />
* The earth is not affected evenly by cosmic radiation, the magnitude of the radiation depends on land altitude and earth's magnetic field strength at any given location, causing minor variation in the local <sup>14</sup>C production. 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.<ref>C. Crowe, ''Carbon-14 activity during the past 5000 years'', ''Nature'', 182, (1958): 470-1. The rebuttals by K. O. Münnich, H. G. Östlund, and [[Hessel de Vries|H. de Vries]], ''Nature'', 182, (1958): 1432-3 and by H. Barker, ''Nature'', 182, (1958): 1433 both maintain that while variations of carbon-14 exist, they are about an order of magnitude smaller than those implied by Crowe's calculations.</ref>
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 [[dendrochronology|dendrochronological]] age. Calibration techniques based on tree-ring samples have contributed to increase the accuracy since 1962, when they were accurate to 700 years ''at worst''.<ref>Libby, W.F. ''Radiocarbon; an Atomic Clock'', Annual Science and Humanity journal, 1962.</ref>
== Speleothem studies extend <sup>14</sup>C calibration ==
Relatively recent (2001) evidence has allowed scientists to refine the knowledge of one of the underlying assumptions. A peak in the amount of carbon-14 was discovered by scientists studying [[speleothem]]s in [[cave]]s in the [[Bahamas]]. [[Stalagmite]]s are [[calcium carbonate]] deposits left behind when seepage water, containing dissolved [[carbon dioxide]], evaporates. Carbon-14 levels were found to be twice as high as modern levels<ref>Pennicott, K., ''[http://physicsweb.org/articles/news/5/5/7/1 Carbon clock could show the wrong time]'', PhysicsWeb, 10 May 2001</ref>. These discoveries improved the calibration for the radiocarbon technique and extended its usefulness to 45,000 years into the past<ref>Jensen, M. N., ''[http://www.physics.arizona.edu/physics/public/beck-citizen.html Peering deep into the past]'', The University of Arizona, Department of Physics (2001)</ref>.
== Examples ==
*[[Ancient footprints of Acahualinca]]
*[[Chauvet Cave]]
*[[Dolaucothi]]
*[[Haraldskær Woman]]
*[[Kennewick Man]]
*[[Roopkund|Skeleton Lake]]
*[[Shroud of Turin]]
*[[Thera eruption]]
*[[Vinland map]]
== See also ==
* [[Age of the Earth]]
* [[Cosmogenic isotope]]s
* [[Environmental isotopes]]
* [[Exponential decay#Measuring rates of decay: half-life and average lifetime|Discussion of half-life and average-life or mean-lifetime]]
== Notes ==
{{reflist|2}}
== References ==
<!-- these references need to be integrated into the text; all appear relevant, but this needs to be properly explained in the article main text; otherwise they should probably be deleted (or commented out; he equivocates) Only delete if found to not be supportive of the article or frivolously added.-->
*{{cite book |title=Interpreting the Past: Radiocarbon Dating |last=Bowman |first=Sheridan |authorlink= |coauthors= |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0520070372 |pages= }}
*{{cite journal |last=Currie |first=L. |authorlink= |coauthors= |year=2004 |month= |title=The Remarkable Metrological History of Radiocarbon Dating II |journal=J. Res. Natl. Inst. Stand. Technol. |volume=109 |issue= |pages=185–217 |doi= |url=http://nvl.nist.gov/pub/nistpubs/jres/109/2/j92cur.pdf |accessdate= |quote= }}
* de Vries, H. L. (1958). "Variation in Concentration of Radiocarbon with Time and Location on Earth", ''Proceedings Koninlijke Nederlandse Akademie Wetenschappen'' B, 61: 94-102; and in Researches in Geochemistry, P. H. Abelson (Ed.) (1959) Wiley, New York, p. 180.
*{{cite journal |last=Friedrich |first=M. |authorlink= |coauthors=''et al.'' |year=2004 |month= |title=The 12,460-Year Hohenheim Oak and Pine Tree-Ring Chronology from Central Europe—a Unique Annual Record for Radiocarbon Calibration and Paleoenvironment Reconstructions |journal=Radiocarbon |volume=46 |issue= |pages=1111–1122 |id= |url= |accessdate= |quote= }}
* Gove, H. E. (1999) ''From Hiroshima to the Iceman.'' The Development and Applications of Accelerator Mass Spectrometry. Bristol: Institute of Physics Publishing.
*{{cite journal |last=Kovar |first=Anton J. |authorlink= |coauthors= |year=1966 |month= |title=Problems in Radiocarbon Dating at Teotihuacan |journal=American Antiquity |volume=31 |issue= |pages=427–430 |id= |url=http://www.jstor.org/pss/2694748 |accessdate= |quote=|doi=10.2307/2694748 }}
*{{cite journal |last=Lerman |first=J. C. |authorlink= |coauthors=Mook, W. G.; Vogel, J. C.; de Waard, H. |year=1969 |month= |title=Carbon-14 in Patagonian Tree Rings |journal=Science |volume=165 |issue=3898 |pages=1123–1125 |doi=10.1126/science.165.3898.1123 |url= |accessdate= |quote=|pmid=17779805 }}; Lerman, J. C., Mook, W. G., and Vogel, J. C. (1970) Proc. 12th Nobel Symp.
*{{cite journal |last=Lorenz |first=R. D. |authorlink= |coauthors=Jull, A. J. T.; Lunine, J. I.; Swindle, T. |year=2002 |month= |title=Radiocarbon on Titan |journal=Meteoritics and Planetary Science |volume=37 |issue= |pages=867–874 |id= |url= |accessdate= |quote= }}
*{{cite journal |last=Mook |first=W. G. |authorlink= |coauthors=van der Plicht, J. |year=1999 |month= |title=Reporting <sup>14</sup>C activities and concentrations |journal=Radiocarbon |volume=41 |issue= |pages=227–239 |id= |url=http://digitalcommons.library.arizona.edu/index.php/objectviewer?o=http://radiocarbon.library.arizona.edu/Volume41/Number3/azu_radiocarbon_v41_n3_227_239_v.pdf |accessdate= |quote= }}
* Weart, S. (2004) ''[http://www.aip.org/history/climate/Radioc.htm The Discovery of Global Warming - Uses of Radiocarbon Dating]''.
* Willis, E.H. (1996) ''[http://www.quaternary.group.cam.ac.uk/history/radiocarbon/ Radiocarbon dating in Cambridge: some personal recollections. A Worm's Eye View of the Early Days]''.
== External links ==
*[http://www.radiocarbon.org/ ''Radiocarbon'' - The main international journal of record for research articles and date lists relevant to 14C]
*[http://www.c14dating.com/ C14dating.com - General information on Radiocarbon dating]
*[http://www.nosams.whoi.edu/about/carbon_dating.html NOSAMS: National Ocean Sciences Accelerator Mass Spectrometry Facility at the Woods Hole Oceanographic Institution]
*[http://c14.arch.ox.ac.uk/calibration.html Discussion of calibration] (from U Oxford)
*[http://www.radiocarbon.org/Info/index.html Several calibration programs can be found at www.radiocarbon.org]
*[http://www.calpal-online.de CalPal Online (Cologne Radiocarbon Calibration & Paleoclimate Research Package)]
*[http://c14.arch.ox.ac.uk/oxcal.html OxCal program (Oxford Calibration)]
*[http://radiocarbon.ldeo.columbia.edu/research/radiocarbon.htm Fairbanks' Radiocarbon Calibration program (for prior to 12400 BP)]
*[http://id-archserve.ucsb.edu/anth3/courseware/Chronology/08_Radiocarbon_Dating.html Notes on radiocarbon dating, including movies illustrating the atomic physics] (from UC Santa Barbara)
{{Chronology}}
[[Category:Radiometric dating]]
[[Category:Radioactivity]]
[[Category:Carbon]]
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[[el:Ραδιοχρονολόγηση]]
[[es:Datación por radiocarbono]]
[[eo:Karbono 14]]
[[fr:Datation par le carbone 14]]
[[ko:방사성 탄소 연대 측정법]]
[[id:Penanggalan radiokarbon]]
[[is:C-14 aldursgreining]]
[[it:Metodo del carbonio-14]]
[[he:תיארוך פחמן-14]]
[[hu:Radiokarbon kormeghatározás]]
[[ml:കാര്ബണ് പഴക്കനിര്ണ്ണയം]]
[[nl:C14-datering]]
[[ja:放射性炭素年代測定]]
[[no:Karbondatering]]
[[pl:Datowanie radiowęglowe]]
[[ru:Радиоуглеродный анализ]]
[[simple:Radiocarbon dating]]
[[sk:Uhlíková metóda C14]]
[[fi:Radiohiiliajoitus]]
[[sv:C14-metoden]]
[[ta:கதிரியக்கக்கரிமக் காலக்கணிப்பு]]
[[tr:Radyokarbon tarihleme yöntemi]]
[[uk:Радіовуглецеве датування]]
[[zh:放射性碳定年法]]