444
Radiation in Art and Archeometry D.C. Creagh and DA, Bradley (editors) © 2000 Elsevier Science B.V. All rights reserved.
AMS dating in archaeology, history and art C. Tuniz a *, U. Zoppi3 and M. Barbetti b
aAustralian Nuclear Science & Technology Organisation, Physics Division, PMB 1, Menai NSW 2234, Australia
bThe NWG Macintosh Centre for Quaternary Dating, Madsen Bldg F09, University of Sydney, NSW 2006, Australia
Radiocarbon (14C) dating provides an absolute time scale for human history over the last 50,000 years. Accelerator Mass Spectrometry (AMS), with its capacity to analyse l4C in sub-milligram carbon samples, has expanded enormously the applicability of this dating method. Specific molecular compounds extracted from ancient bones, single seeds and other microscopic carbon-bearing substances of archaeological significance can now be dated, increasing the sensibility and reliability of the chronological determination. Thanks to the very limited invasiveness of AMS, rare artefacts can be sampled for dating without undue damage. The state of the art in AMS dating of objects significant for archaeology, history and art is reviewed with examples from some recent applications.
1. INTRODUCTION
One of the main objectives of archaeology is to chronologically order past events by studying material remains that reflect human behaviour. A versatile array of dating methods is nowadays available. Relative chronologies can be deduced from circumstantial evidence, such as change of style and manufacturing technique. Relative chronological information can also be obtained using methods based on time-dependent geological and chemical changes (eg stratigraphy, sedimentation rate, weathering, hydration, magnetism). Certain kinds of annual phenomena, such as tree rings or varves, will yield very precise chronologies if stringent precautions are followed. Finally, many methods providing absolute chronologies are based on time-dependent phenomena related to natural radioactivity, and include:
1. exponential decay of long-lived cosmogenic radionuclides, as in the radiocarbon method;
2. exponential in-situ production by secondary cosmic rays of long-lived radionuclides, such as 10Be,26Al and 36C1, which can be used for dating rock surfaces and stone artefacts;
Present address: Australian Permanent Mission to the United Nations, Mattiellistrasse 2-4/m A-1040 Vienna, Austria
445
3. linear build-up of radiation exposure effects, in thermoluminescence (TL), optically stimulated luminescence (OSL), electron spin resonance (ESR) and fission track dating;
4. exponential build-up of a radiogenic daughter from a primordial radionuclide, in K-Ar, Ar-Ar and U-series dating.
I4C is the most widely used of these chronometers. In the late 1940s, the development of radiocarbon dating by detection of the 14C residual activity (Libby, 1946; Arnold and Libby, 1949) revolutionised archaeology providing a precise and direct measurement of the time scale for the development of human activities during the late Quaternary. In particular, radiocarbon dating had a strong impact on the understanding of European prehistory, previously dated only by correlation with the historical chronology of the Near East (Renfrew, 1973)
In the late 1970s (Muller, 1977; Bennett et al, 1977; Nelson et al, 1977), the development of direct atom counting by AMS enhanced more than a million-fold the sensitivity of 14C analysis. Extensive AMS work followed, particularly in the analysis of radiocarbon and other cosmogenic radionuclides for archaeological, geological and environmental applications (Tuniz et al, 1998; Fifield, 1999). Through the non-invasive analysis of famous artefacts and findings such as the Shroud of Turin (see Figure 1; Damon et al, 1989), the Ice Man (Prinoth-Fornwagner and Niklaus, 1994) and the Dead Sea Scrolls (Bonani et al, 1992), AMS has gained widespread public recognition as a dating technique.
Figure L Close up of the facial image of the Shroud of Turin as it appears on a photographic negative (photo: © 1978 Barrie M. Schwortz).
446
Radiocarbon dating must be applied with due consideration for contamination, bioturbation, natural isotopic fractionation and many other factors that can influence its accuracy. Appropriate procedures to correct for these effects have been established. In the following, AMS dating will be reviewed with some illustrations that draw on the special advantages of this method to determine a precise chronology for human prehistory. The application of AMS dating to authenticate objects and materials of historical and artistic significance will be also discussed.
2. PRINCIPLES OF RADIOCARBON DATING
i4C is formed in the atmosphere by nuclear reactions of secondary cosmic neutrons with nitrogen (78 % of the atmosphere consists of N2) and is quickly distributed throughout the atmosphere as 14C02. In pre-industrial times, the atmospheric isotopic ratio 14C/12C was about 1.2 x 10"12. In a simplified model, which is not strictly correct (see sections 4. and 5.) but is often used to introduce the basic idea, we may argue that living organisms participating to the carbon cycle via metabolic processes are characterised by this radiocarbon concentration. When a living organism dies, the carbon exchange stops. Hence, by measuring the residual 14C concentration in organic samples, if they have not been contaminated by younger material (eg via bacterial action, soil organic acids) or older material (eg geologic calcium carbonate), it is possible to calculate the time elapsed since the material was originally formed. Ages up to about 50,000 BP can be determined by radiocarbon dating.
2.1. Radiocarbon: a gift of nature
The functioning of radiocarbon as a precise natural chronometer in archaeology is due to a number of favourable circumstances. Firstly, the 14C half-life of 5730 years is ideal for studies in the temporal scale characterising the development of human civilisation. Furthermore, the rather rapid and homogeneous mixing in the atmosphere of the freshly produced 14C02 gas attenuates production variations. Hence, the time zero point of the chronometer (the initial isotopic ratio in living organisms) is fairly uniform in space and time. Finally, incorporation of 14C within organic molecules permits the extraction of material for dating which is directly derived from the original living organism.
In principle, other natural long-lived radioisotopes could be useful to extend the datable time span in archaeology. In particular, the cosmogenic isotope 41Ca was measured by AMS in modern bones and other terrestrial materials to test the possibility of directly dating archaeological findings with ages of 105 - 106 years (Middleton et al, 1989). Unfortunately, the variability of the 41Ca/40Ca ratio in contemporary materials makes it difficult to establish the time zero point for this chronometer.
3. AMS: COUNTING ATOMS RATHER THAN DECAYS
AMS is the analytical technique of choice for the detection of long-lived radionuclides in samples which cannot be practically analysed with decay counting or conventional mass
447
spectrometry (MS). Its advantage is that the ambiguities in ion identification are practically removed, enabling the analysis of isotopic ratios as low as 10"15, a factor 105 lower than in most MS systems. Since the atoms and not the radiation resulting from their decay are directly counted, the sensitivity of AMS is unaffected by the half-life of the isotope being measured and detection limits at the level of 106 atoms are possible. Compared to the decay counting technique, the efficiency of AMS in detecting long-lived radionuclides is 105 - 109 times higher, the size of the sample required for analysis can be 103 - 106 times smaller and the measurement can be performed 100 to 1000 times faster. For example, samples having as little as 20 • g carbon are analysed in 30 minutes at the ANT ARES AMS centre (see Figure 2). To highlight the difference between decay counting and atom concentration analysis, consider 1 g of modern carbon containing 6 x 1010 atoms of 14C, which can be measured by decay counting with 1% precision (104 decays detected) in 1000 minutes hours. With a high-intensity ion source, AMS can count 104 14C atoms in one minute, consuming only 100 • g of the source material.
Figure 2. The Tandem Accelerator in use at the ANTARES AMS centre (Australian Nuclear Science and Technology Organisation, Sydney; Tuniz et al, 1995).
3.1. Choice of accelerator
In AMS, the intrinsic analytical properties of ion accelerators are exploited to perform ultra-sensitive isotopic analyses.
Van de Graaff tandem electrostatic accelerators are the optimum choice for a variety of AMS applications. Tandem accelerators working between 0.5 - 3 MV have been specifically designed for 14C analysis (Purser, 1994; Suter, 1999). Large tandem accelerators, originally
448
developed for nuclear physics research, are also used to analyse a variety of rare radionuclides (Tuniz et al, 1995) with the advantage of allowing higher energies and a more effective separation of isobaric interferences.
Other accelerators, such as cyclotrons, were unsuccessfully used in early attempts to measure long-lived cosmogenic radioisotopes at natural 14C levels. Only recently, an AMS system based on a small cyclotron has been developed to detect 14C at natural abundances (Chen et al, 1999). However, its practical use is limited and further developments will be required to allow precise measurements of isotopic ratios.
3.2. Radiocarbon analysis with tandem Van de Graaff accelerators
A typical AMS set-up is shown in Figure 3. Negative carbon ions are produced in the caesium sputter ion source and, after low-energy mass analysis, are injected into the tandem accelerator. In the case of l4C, isobaric interferences are completely eliminated because 14N does not form stable negative ions. High precision AMS measurements are carried out either
( 4 -i ^ .     -I "i .....
by using simultaneous injection or by rapid sequential injection of the isotopes C, C and 14C. Negative ions are attracted to the positive voltage on the terminal and thereby accelerated to energies between 0.5 - 15 MeV, at which point they pass through a low pressure gas or a thin carbon foil and are stripped of some of their electrons. Multi-charged positive ions are then further accelerated away from the same positive terminal voltage. The stripping process is used to destroy molecular interference which is the main limitation for conventional mass spectrometry. After the acceleration stage, a magnet selects the most probable charge state (typically 3+ or 4+, depending on ion energy). Velocity or energy analysers provide additional filtering to remove residual background. Finally, identification of the 14C ions is performed in an ion detector. The isotopic ratio 14C/12C (or 14C/13C) is derived from the 14C counting rate in the detector and the 12C and 13C beam currents measured in Faraday cups. A similar methodology is used to analyse other rare cosmogenic radionuclides, such as 10Be, 26Al, etc.
Figure 3. Scheme of the ANTARES AMS facility as used for 14C AMS (Tuniz et al,
449
Reaction Unit
Figure 4. Scheme of the graphitisation line using the Zn/Fe method.
4. SAMPLES FOR AMS 14C ANALYSIS
Organic samples to be analysed by AMS need to be purified and transformed into a graphite target for the ion source. Most samples require treatment to remove extraneous carbon or to extract fractions containing only original carbon compounds. C02 is obtained from the purified sample either by combustion or hydrolysis. Finally, CO2 is reduced to graphite via a catalytic process with Fe or €0 in the presence of Zn (see Figure 4) and/or hydrogen (Jull et al., 1986; Jacobsen et al, 1997). CO2 rather than graphite can be also used, eliminating the need of converting gas to graphite (Bronk-Ramsey and Hedges, 1997). However, only low ion currents are achievable, considerably limiting the analytical throughput.
4.1. What is being dated?
The degree to which AMS dated samples are representative of a specific past event is crucial to the satisfactory interpretation of the results. Some of the archaeological materials that have been studied illustrate the importance of the small sample capability. In particular
1. individual amino acids extracted from bone or blood can sometimes provide a better basis for radiocarbon dating than the use of all organic material;
2. individual seeds can be directly dated instead of using neighbouring pieces of charcoal;
3. tiny pieces of charcoal, extracted from inclusions in ceramics can directly date the object of interest;
4. a small number of foraminifera shells (or pollen grains) of one species can be selected under a microscope and used to date sediment layers with good time resolution
The interpretation of 14C measurements, including the potential for contamination, depends on the molecular species that are extracted and used to date the original sample. The
450
small sample capability of AMS increases the need for careful study of the material used for dating and provides the means for making detailed assessments of the differences hi 4C content of various molecular species present in a sample.
An important example is the radiocarbon dating of bones. Buried bones are easily contaminated by carbonates from the surrounding soil. A simple extraction of the original organic components such as collagen may not be sufficient, as complex molecules, including proteins present in ground-waters and various soluble carbonaceous materials, may also penetrate the bone. To limit this kind of contamination, methods based on the isolation of carbon atoms forming intact peptide bonds in bone proteins have been developed (Nelson, 1991).
A simpler approach is to date all organic carbon whilst avoiding any inorganic components. For example Russ et al. (1990) have developed a method for using a low-temperature (100 °C), low-pressure (4 torr) oxygen plasma to selectively oxidise the organic carbon in small samples of pigments from prehistoric rock paintings to C02 for AMS dating.
Nelson et al. (1986) reported the use of AMS to obtain radiocarbon dates for blood residues on prehistoric stone tools. In one case, involving blood from a snowshoe hare, the {4C date (1010 ± 90 BP) was in good agreement with measurements on charcoal from a closely associated hearth (1060 + 160 BP). Only 50 |ig of carbon, extracted from high molecular weight proteins, was obtained in the second case of human blood from a chert tool and this proved sufficient to obtain a date (2180 + 160 BP) compatible with expectations.
Another important issue to consider is the biological aging process. The 14C concentration of living tissues is fixed as it is formed. Thereafter the cells and bone carbonate in animals are renewed very slowly by the metabolic processes, while radioactive decay of the fixed l4C is continuously lowering the initial level. The net result is that the 14C content lags the atmosphere by up to a few decades. In the case of growing trees, cells formation happens only in a narrow zone under the bark, so the innermost wood may already be centuries old before the tree dies. In some but not all species, there is a clear ring boundary corresponding to each year. This forms the basis of dendrochronology and explains why wood is so widely employed for radiocarbon calibration studies.
5. PERFORMANCE AND LIMITATIONS OF AMS 14C DATING
The attributes of AMS 14C dating which are most significant for archaeological applications are sample size, datable time span and dating accuracy.
Material	Quantity*	Materia!	Quantity*
Wood	5	Shell, Carbonates	10
Bone	500	Paper, textiles	5-10
Charcoal	3-5	Grass, seeds, leaves, grains	5-10
Beeswax	1-2	Hair, skin	5-7
Pollen	1	Teeth, tusk, ivory	500-700
milligrams for AMS, grams for decay counting
451
5.1. Sample size
Sample sizes required for AMS, as reported in Table 1 for some archaeologically significant carbonaceous materials, are generally 1000 times smaller than those required for decay counting and samples as small as 20 ug carbon can be processed. While the use of small samples greatly extends the applicability of i4C dating, contamination in the field and during chemistry processing may limit both accuracy and datable time span.
5.2. Datable time span
Oxidation and graphitisation processes are responsible for a background equivalent to about 1 |lg modern carbon. This sets an equivalent age limit of about 50,000 BP for 1 mg specimens. On the other hand, measurements carried out with geological (i.e. 14C-free) unprocessed graphite give results equivalent to an age of 60,000 to 70,000 BP, and accelerator background (with no sample) is equivalent to an age of 80,000 to 90,000 BP. Hence, the datable time span by AMS 14C could, in principle, be extended beyond the present limits. This extension would be very valuable for studying early activities of Homo sapiens sapiens in order to corroborate results from other dating techniques such as OSL and U-series dating (for a comparison of the datable time span for different dating techniques see Figure 5). Recent studies suggest that the use of a stepped combustion technique could further reduce the contamination (Bird et al, 1999). Pre-treatment of the glassware by baking it under streaming oxygen also showed a beneficial effect (Lawson et at, 1999).
<^   Pal aeomagnetisro <^ Fission track
Potassiuni-ar^on <^Varves^>
"^'q",|ri(j ;ffg;e exposure dating ^>
JOL?.g?.'!.<?lyj?i|[!?^cence/ gjffiffi.?.?)1. sP'n resonance
Amino acid racemizatiort ^>
Radiocarbon ^>
Obsidian liydration ^> pendrochronology ^>
Archaeomagnetism ^
I I I 11 Hi]-! I I jUHJ-1 I I |M;|-1 I ! ] HMj    1 II [i
lO3 10* 10s l<f 10?
Figure 5. Comparison of the datable time span of different dating techniques.
452
5.3. Precision and accuracy
The precision of AMS radiocarbon measurements is usually dominated by statistical error. A minimum mass of about 20 jxg is necessary to date recent (< 5000 BP) specimens with an error of 1% (~ 80 a). With the use of multiple graphite targets obtained from the same material, AMS has demonstrated the capability to provide a precision of 0.2 % ( < 20 a) for the radiocarbon analysis of modern samples. However, there are a number of systematic effects which must be considered to obtain an accurate age. These effects are briefly discussed in the following.
5.3.1. Contamination
As mentioned above, due to the small mass of material used in AMS measurements, the oxidation and graphitisation processes inevitably lead to contamination by modern CO2. It is essential to assess the contamination level introduced by each type of procedure by processing a blank material (eg coal, graphite, marble etc.). A correction can then be applied (see Figure 6). For contamination of modern origin, the correction is small for recent samples and large for older samples. It ultimately limits the maximum age of the materials which can be dated.
5.3.2. Fractionation
Natural chemical or physical processes can mass fractionate the carbon isotopes during carbon uptake and alter the 13C/12C and 14C/12C isotopic ratios. Natural mass fractionation is expressed in terms of 813C which is a measure (in parts per thousand) of the deviation of the isotope ratio C/ C from a standard material referred to as PDB, a Cretaceous belemnite, Belemnitella americana, from the Pee Dee formation of South Carolina (Olsson, 1970). Typical 513C values for environmental materials can vary between +2 permil (eg marine
60000
55000 -
o 40000 -
CO
« 50000 -
35000 -
30000
0.00
0.20
0.40
0.60
0.80
1.00
Sample mass [mg]
Figure 6. A typical background corresponding to the contamination introduced by the chemical procedures.
453
carbonate) to -27 permil (eg some kinds of wood). This effect is significant and must be taken into account to obtain accurate ages. The 513C value for a material to be radiocarbon dated must be known to correct for the fractionation affecting the 14C isotopic ratio. Additional fractionation may be introduced by chemistry processing of AMS samples (eg incomplete graphitisation) and during AMS analysis (eg ion sputtering and stripping processes). In general, these effects are corrected by processing and measuring standard materials of known isotopic ratio such as the oxalic acid HOxI (Stuiver, 1983).
5.3.3. Reservoir effects
Organic specimens drawing carbon from reservoirs other than the atmosphere may yield incorrect ages. In the case of marine shells deriving their carbon from seawater, a system not in equilibrium with the atmosphere, the reservoir effect leads to age differences of up to 1000 years (Stuiver et al, 1998b). This difference can be reflected in bones of animals or humans consuming fish. High apparent ages can be found in plants near volcanoes erupting l4C-depleted CO2. Other small age shifts arise from differences in atmospheric mixing between northern and southern hemispheres, and regional air-sea exchange of C02.
5.3.4. Variation in 14C production rate (calibration)
Conventional radiocarbon ages are reported in years before present (BP), where present is 1950 AD, and are calculated using the "Libby" half-life of 5568 years on the assumption that the production of l4C in the past has been constant (Donahue et al, 1990). The difference between conventional radiocarbon ages and calendar ages (calibrated ages) has been determined with high precision for all of the Holocene by radiocarbon measurements on tree ring samples (see Figure 7; Stuiver et al, 1998a), which are independently and precisely dated by dendrochronology. Part of this difference derives from the use of the conventional
Calendar age [AD]
Figure 7. The calibration curve for the last two millennia (Stuiver et al, 1998a).
454
half-life, which is known to be 3% too small. The remaining difference derives from secular variations of 14C production rate in the atmosphere due to geo- and helio-magnetic effects and global variations in the parameters of the carbon cycle. In the range 1650 - 1950 AD calibrated ages are ambiguous due to fluctuations in atmospheric 14C concentration. Samples with conventional radiocarbon ages of 200 years or less are often reported as 'modern' (Stuiver and Polach, 1977). A radiocarbon calibration for the late Pleistocene has been obtained by comparing radiocarbon results to ages obtained by Uranium/Thorium (Bard et al, 1998) and varve (lacustrine annual sedimentary layers) chronology (Kitagawa and van der Plicht, 1998; Hughen et al, 1998). Radiocarbon ages are younger than calendar ages during the late Pleistocene, with a difference of 1000-2000 years between 15,000 and 10,000 BP.
6. THE IN SITU METHOD
Long-lived radioisotopes such as 14C, 10Be (1.50 Ma half-life), 26A1 (720 ka), 36C1 (310 ka) and 41Ca (103 ka) are produced in situ in the shallow horizons of the Earth by interaction of secondary cosmic rays (mainly neutrons and muons) with suitable target nuclides in rocks and soil. Typical production rates at sea level and high latitudes are discussed in Tuniz et al. (1998). AMS is used to determine the radioisotope concentration and subsequently estimate the exposure age of the rock surface. The in-situ method works best on the time period from 5 ka to 5 Ma. The lower limit is set by the sensitivity of AMS. In principle, this method could be used to set an upper limit to the age of rock carvings or paintings. However, the practical limits are determined by the strong dependence on geographic location (latitude and altitude), on shielding conditions and on erosion rates. The analysis of the depth profile of a radionuclide or the measurement of the concentration of two radionuclides with different half lives can be used to determine erosion rate, exposure age and history of a surface.
One of the first archaeological applications of the in situ method was the determination of a limit age of the petroglyphs found in the Coa Valley in Portugal (Phillips et al, 1997). 36C1 exposure ages showed that the rock panels were available for engraving during the Palaeolithic, supporting the Palaeolithic origin inferred by the archaeologists (Zilhao, 1995). The in situ method was also applied to the dating of the Tabun Cave, Mt. Carmel in Israel (Boaretto et al, 1999). The sediments in the cave are of aeolian origin and are rich in quartz. To study the burial history,26Al and 10Be concentrations were measured in sediment samples and flint tools.
7. AMS 14C DATING IN PREHISTORY
Radiocarbon dates are the main source of the time perspective in prehistory Although AMS 14C dating cannot access the earliest human developments occurring at the order of 100,000 BP and beyond, it can reach a highly significant era in human prehistory. It was during the last 50,000 years that Homo sapiens sapiens, or modern humans, colonised large habitable parts of our planet. In the following we briefly discuss the contribution of AMS 14C dating to the construction of a chronology for the spread of modern humans, including the
455
early manifestations of civilisation, viz. the capacity of representing and interpreting the reality through rock pictographs.
7.1. Early human migrations
When Homo sapiens sapiens colonised America, Europe and Australia is a matter for controversy at present.
The study of human bones in North American sites originally provided a wide range of dates from less than 20,000 BP up to 70,000 BP, with many of these results obtained by amino-acid racemisation and 14C decay counting. It must be noted that radiocarbon dating of ancient bones is unreliable unless specific amino acids are extracted. AMS dating of such minute components extracted from the same bones gave results around 11,000 BP at the oldest (Taylor, 1987). This strengthened the common view that the north American continent was populated not much before the Holocene period, when an ice-free land corridor was opened across the Bering Strait at the end of the last ice age. More work is needed to support these theories as the validity of AMS 14C dates on poorly preserved fossil bones remains questioned (Stafford et ai, 1990). In recent years, the debate has been re-opened and many archaeologists now accept the date 12,500 BP for the far southern site of Monte Verde in Chile (Adovasio and Pedler, 1997).
Palaeoanthropologists are interested in the origins of Homo sapiens sapiens in Europe and its relation to the hominids of Neanderthal type. AMS has been used to date bones from the Upper Pleistocene to reconstruct the human evolution in this part of the world (Stringer, 1986). The Mousterian - Aurignacian boundary has been dated at about 37,000 BP in Spain (Bischoff et ai, 1994) by AMS 14C analysis of charcoal fragments. These dates are at the fringes of the radiocarbon method but they have been confirmed by U-series dating on the enclosing carbonate. The latter method yields a date of about 43,000 BP, a difference which may be partly explained by 14C production variations due to geomagnetic field fluctuations and climatic changes. The evolutionary fate of the Neanderthals and the spread of Homo sapiens sapiens has been recently reviewed by Pettitt et al. (1999).
Concerning the first colonisation of Australia, many archaeologists agree on the idea that the first humans entered via the north of the continent, Cape York, Arnhem Land or the Kimberley. Much less agreement exists on the time frame of this colonisation. Until recently, the most ancient radiocarbon dates for the human presence in Australia corresponded to less than 40,000 BP, as shown by AMS dates from the Kimberley region (O'Connor, 1995) and from Chillagoe in the Cape York peninsula (David et al, 1997). On the other hand, optically stimulated luminescence yields dates corresponding to 50,000-60,000 BP for sites in the Northern Territory (Roberts et al, 1994). In addition, ESR and U-series dating investigations on the Lake Mungo 3 human skeleton yielded a date of 62,000 ± 6000 BP, in good agreement with OSL age estimates on the sediments into which the skeleton was buried (61,000 ± 2000 BP) (Thorne et al, 1999). This is arguably the earliest known human presence in Australia. The difference between the dates inferred by radiocarbon and other dating methods for the earliest presence of humans in Australia is too large and it cannot be explained by astrophysical or environmental effects on l4C concentration in the atmosphere during the late Pleistocene. Various theories have been advanced to explain this discrepancy, including the hypothesis that Australia was colonised in two or more separate human migrations (Allen and Holdaway, 1995). The association between rising seas in the Austral region, around 60,000,
456
80,000 and 100,000 years ago, and human occupation of the Australian continent, have also been considered (Chappell, 1993). Recent 14C AMS dates show that the Devil's Lair site in South Western Australia was occupied by aboriginal people 48-49 ka BP, supporting the hypothesis of an early human colonisation of Australia (Turney et al., 2000).
7.2. Prehistoric rock art
Dating rock art is essential to building archaeological models describing the evolution of prehistoric civilisation. The antiquity of European cave paintings was qualitatively established since last century. Relative chronologies were developed using stylistic criteria and the status of the pigments or the presence of Figures, such as extinct fauna, of known antiquity. Some indirect chronological information was then obtained by radiocarbon dating of human occupation remains found near the paintings. However, the real test was to date actual pigments or, better still, organic components of pigments which are likely to have derived from the painters or other contemporary carbon. However, location and extraction of material that has not been contaminated since its original application, which carries a radiocarbon signature unique to that moment, and which has not become part of a complex sequence of updates or overpainting is an enormous challenge. Only recently, direct dating of the charcoal used for the drawings was possible thanks to the sensitivity of AMS 14C dating.
Dates in the range 12,900 - 14,000 BP (Valladas et al., 1992) were obtained for pictures of bison in the Spanish caves of Altamira and El Castillo and in the French Pyrenean cave of Niaux. On the other hand, remains of human occupation in the same caves range approximately from 5,000 to 18,000 BP.
Some very sophisticated Palaeolithic paintings were discovered in 1994 in the Ardeche Valley in France (Chauvet-Pont d'Arc cave). Between 300 and 400 animals are depicted with advanced techniques (including the use of perspective), such as rhinoceros, lions, mammoths, horses and bison. AMS radiocarbon dating using microscopic samples of charcoal from the paintings yield a consistent age of about 31,000 BP for several of these animals (Clottes et al, 1995). Pieces of charcoal found on the ground in the cave yield dates of 22,000 - 29,000 BP, suggesting human incursions for extended periods of time. The radiocarbon dates obtained are the oldest found for prehistoric rock art and confirm that Homo sapiens sapiens created elaborate forms of art long before the Upper Palaeolithic.
7.2.1. Australian rock art
The Australian program in AMS dating of rock art includes research into the probable age of the rock art of Chillagoe and Laura (North Queensland), the Kimberley (Western Australia) and Olary District (South Australia). A variety of materials is being analysed, including pigments, oxalate minerals, silica coatings, plant fibres, carbonised plant matter, fatty acids, beeswax and mud-wasp nests. Different sample processing techniques are being explored, including low-pressure plasma techniques and laser extraction methods. Laser-induced combustion and AMS have been used to date single laminae in 2 mm thick rock surface accretions, a very useful method to study prehistoric paintings and engravings (Campbell et al, 1996). AMS dating on charcoal drawings from Chillagoe yield ages of less than 1000 years, supporting the hypothesis of population increase and intensified use of this region during the late Holocene (David et al, 1999).
457
7.2.1.1. Bradshaw rock art
The Bradshaws are Australian Aboriginal rock paintings with a unique style characterised by elegant and graceful Figures with many ornaments and accoutrements. An example is shown in Figure 8. Paintings of this style are found in the Kimberley region in the north west of the state of Western Australia. The paint colour is usually a light mauve or mulberry. These Figures were first reported by early explorer Joseph Bradshaw who, accompanied by his brother, surveyed this region in 1891. The paintings are so unusual and distinctive that there has been much speculation and debate concerning their origins and meanings. Some researchers have gone as far as to suggest origins other than the ancestors of modern indigenous Australians.
Despite the considerable interest no scientific attempts to date the paintings were made until 1997, primarily because of the difficulties inherent in dating rock paintings. The ANTARES AMS team was involved in two separate investigations. Watchman et al. (1997) dated carbon-bearing material scraped from on or near paintings. The conclusion was that the Bradshaw paintings are at least 4,000 years old.
Figure 8. Computer enhanced "Tassel" Bradshaw Figures showing their ornate form of dress with rear triple tassels, bangles, elbow bands, cummerbund waistbands with pubic aprons and complicated head-dresses. A mud-wasp nest can be seen on the rock face just above the left hand Figure. Photo: courtesy of Graham Walsh, Takarakka Rock Art Research Centre.
458
These dates are somewhat at odds with the findings of the second investigation in which Roberts et ah, (1997) made use of the nests of mud-wasps to provide a limit for the age of a Bradshaw painting. Two measurement techniques were involved in this investigation -radiocarbon AMS and OSL. The investigators found a minimum age of 17,000 BP. So the origins of the Bradshaw paintings are still unknown and further (perhaps many) measurements to establish their ages will be required.
Fig. 9. The Jinmium rock shelter. Photo: courtesy of Richard Roberts, La Trobe University.
7.2.1.2. Jinmium
The Jinmium rock shelter is located in the northern region of Australia under a tilted block of sandstone (see Figure 9). Circular engravings (pecked cupules) have been carved by the early inhabitants of this remote area. Thermoluminescent dating provided ages of 50,000 -70,000 BP for the quartz sand associated with the buried engravings. Dates between 116,000 and 176,000 BP were provided by TL for the quartz sands of the artefact bearing sedimentary deposits near the rock shelter (Fullagar et al, 1996).
These results were subsequently contradicted using other dating techniques. Optically Stimulated Luminescence (OSL) applied to single sand grains indicated that the Jinmium deposits are younger than 10,000 BP. AMS 14C dating of the carbon fragments in the deposits provided similarly young ages (Roberts etal, 1998).
459
7.3. The ice man
The mummy of a human body (see Figure 10) was discovered in September 1991 in a glacier, at 3210 m on the Ótzal Alps, Alto Adige Region, Italy. The find is now displayed at the South Tyrol Museum of Archeology (Bozen, Italy) and includes shoes, clothes, a copper axe and a quiver of arrows. AMS was used to date a variety of samples from this find, including grass from the shoes and tissue specimens from the body. Results obtained at a number of laboratories concord on a radiocarbon age of 4546 ± 17 BP (Prinoth-Fornwagner and Niklaus, 1994), corresponding to a calendar age between 3100 and 3350 BC. This result and the style of the artefacts found with the body support the hypothesis that the Ice Man belonged to the Remedello culture present in the northern part of the Italian peninsula during this period.
Figure 10. The mummified corpse discovered in 1991. (photo: Marco Samadelli; © South Tyrol Museum of Archaeology, Bozen, Italy)
460
8. AMS IN HISTORY AND ART
8.1. The Shroud of Turin
The shroud of Turin (Figure 1), held in a church in Turin (Italy), is an object of devotion for many Catholics. The image of a crucified man appears on the textile, considered by the believers to be the burial cloth of Jesus Christ. In 1988, a 10 mm by 70 mm strip of linen was cut, divided in three postage stamp-size samples and distributed to the AMS laboratories in Zurich, Oxford and the University of Arizona in Tucson. The results from the three laboratories agreed on a medieval date, 1290 - 1360 AD, at 90% confidence (Damon et al, 1989). This is close to 1353, the first appearance of the Shroud in historical records. The possibility that the AMS 14C date does not reflect the true age of the Shroud is still being debated. A number of causes, including the 1500s fire and the effect of bacteria and microorganisms, have been considered to explain the younger age. The historical details on the AMS dating of the Shroud of Turin have been given by Gove (1996).
8.2. The Dead Sea Scrolls
The Dead Sea Scrolls are a collection of 1200 parchment and papyrus manuscripts found in 1947 in cave locations close to the Dead Sea. It is believed that they have been written by the Essenes, a religious group belonging to Judaism who lived in the Quman site until the occupation by the Romans in 68 AD. Several manuscripts were dated by means of the C AMS technique (Bonani et at, 1992; Jull et ai, 1995). The measured ages were in good agreement with the dates on the manuscripts (when present) and/or the ages derived by means of palaeographic estimates.
8.3. The Venafro chessmen
The Venafro chessmen, discovered in 1932 in the southern Italian necropolis of Venafro, are among the most controversial chess-related archaeological finds of this century. For more than 60 years, archaeologists have formulated a variety of hypotheses to explain how bone chess pieces of Arabic shape were discovered in a tomb of Roman age. Some scholars claimed that the chessmen were indeed of Roman origin. The chess pieces are preserved in the Archaeological museum of Naples, where a bone fragment of 2 grams was collected for AMS analysis. Radiocarbon measurements carried out at the ANT ARES AMS Centre yielded a calibrated age of 885-1017 AD (68 % confidence level) (Terrasi et ai, 1994), supporting the view that this game was introduced to Central Italy during the Saracen invasions of the 10th century AD.
8.4. Charlemagne's crown
The Iron Crown (see Figure 11) of the first Holy Roman Emperor, Charlemagne, is held in the Cathedral at Monza, near Milan in Italy. The origin and age of the crown, later used to crown Napoleon Bonaparte, are uncertain. Historical records place its origin between the Roman and Middle Ages, a spread of several centuries. In 1996, it was discovered that the precious stones were held in place by a mixture of clay and beeswax, which provided enough carbon for AMS radiocarbon dating. The analysis performed at ANTARES yielded an age between 700 and 780 AD (Milazzo et ai, 1997), consistent with the historical date for the crowning of Charlemagne, 800 AD, on Christmas Night.
461
8.5. Donatello's glue
The Annunciazione Cavalcanti (Cathedral of Santa Croce, Florence) is one of the best known creations of the Italian sculptor Donatello (1386-1466 AD). The sculpture is decorated with a group of terra-cotta cherubs. The base of one of these Figures has large cracks that had been subsequently repaired with a resin glue. It is not known when the accident occurred. The ANSTO results for the glue, 1331-1429 AD (68 % confidence level), proved that the restoration had been performed during the lifetime of the artist. The breakage and repair may therefore have happened when the work of art was created. Italian scholars believe that the cherub cracked because it was not hollowed out before firing and that the repair was carried out by Donatello himself, after damaging the statue in the kiln.
Figure 11. Charlemange's Crown.
8.6. The conquest of Peru
The manuscripts "História et Rudimenta Linguae Piruanorum" and "Exsul Immeritus Bias Valera populo suo'\ which were found in the family papers of Neapolitan historian Clara Miccinelli, are commonly known as the "Miccinelli documents". They discuss events and people associated with the Spanish conquest of Peru (see Figure 12).
As well as containing details about reading literary quipus (documents which were written using a combination of textile ideograms and knots) "História et Rudimenta Linguae Piruanoruni'' (History and Rudiments of the Language of the Peruvians; Laurencich Minelli et at, 1995) makes the incredible claims that Pizarro conquered the region after having Inca generals poisoned with arsenic-tainted wine and then condemned the Inca emperor, Atahuallpa, to death instead of granting him an audience with the King of Spain. The account departs markedly from the long-held version of the event - that Atahuallpa was put to death for ordering the execution of his brother and rival. Furthermore, the manuscript suggests that the chronicler Guamán Porna de Ayala (15387-1620?), author of one of the most important works on Inca Peru, the "Nueva
510401
462
Cordnica y Buen Gobiemo" (New Chronicle and Good Government) written sometimes before 1618, merely lent his name to a work actually written by the Jesuit priest Bias Valera.
Fig. 12. Pizarro on his way to Peru, as portrayed in one of the scenes of a painted panorama in the frieze of the Rotunda of the U.S. Capitol Building (Washington DC).
Valera is also believed to be the author of the manuscript "Exsul lmmeritus Bias Valera populo suó", an account of his own actions. According to this document dated May 10, 1618, Valera was forced to fake his own death in 1597 and, under a false name, was able to live in Peru between 1599 and 1618 and write the "Nueva Corónica y Buen Gobiemo". Attached to "Exsul lmmeritus Bias Valera populo suo" there were:
1. a letter from Francisco de Chaves (Laurencich Minelli et al., 1998), a conquistador and chronicler on Pizarro's expedition; (the letter, dated August 5, 1533, was addressed to Charles V, King of Spain, and is the source of the accusations already suggested in "História et Rudimenta Linguae Piruanoruni" and "Exsul lmmeritus Bias Valera populo suo");
2. a wax box containing a fragment of a letter from Columbus and the contract between Guamán Porna de Ayala and Bias Valera; (under the agreement, Ayala lent his name to Valera after payment of a horse and a chariot);
3. a few literary quipus.
The historical significance of the discovered material is immense and historians considered it to be of primary importance to verify the authenticity. As a part of a worldwide research collaboration ANSTO performed the radiocarbon dating of five samples associated with the Miccinelli documents (Zoppi et al, 1999). The results showed that, with a high degree of confidence, the wax used to seal the letter to the King of Spain originated earlier than 1533 (see Figure 13), the date on the letter. Similarly, the wax used for the box containing the
463
agreement allowing Valera to write "Nueva Cordnica y Buen Gobierno" under a false name, most probably originated before 1618, the accepted completion date of this document.
Fig. 13. The calibration of the wax sample from the seal of the letter to the King of Spain.
9. DATING WITH THE BOMB PULSE
Atmospheric nuclear weapons tests during the 1950s and early 1960s produced a rapid increase in 14C. In the northern hemisphere, the 1963-1964 14C concentration reached a level nearly 100% higher than the pre-bomb level (see Figure 14). Since the Nuclear Test Ban Treaty came into effect in 1963, the atmospheric 14C concentration has been decreasing due to exchange with the biosphere and the oceans (with minor perturbations due to sporadic nuclear tests). Presently, the 14C level has declined to about 110 percent of the pre-bomb level. The shape and intensity of this bomb pulse has been determined by measuring 14C in atmospheric CO2 (Levin et al, 1994; Manning and Melhuish, 1994) tree rings (Hua et al, 1999a&b) and ice cores (Levchenko et al, 1997). The decrease of atmospheric 14C is presently about 80 times faster than radioactive decay.
This well determined temporal change of 14C provides a clock for dating biological materials formed since 1955 AD, and leads to interest in forensic applications. For example, it was shown that it is possible to determine the time of death of humans by using the lipid fraction of bones, which is the most suitable component for dating purposes, thanks to its fast turnover (Wilde?al, 1998).
464
(650 1955 19« IMS »875
ttSO 16!» 5990 1*68 1970 197S
V.ars (AD)
-VMtiun!, AitttM 4T*H, ISTS (58BS-1W3) 0   AtKU, Hunguy <r3S*. JfSSt: (I9B1-OM)
-   .UnM BWe»ta»,*(IH3««rSfSb.f«9i 0  tew****. «<»:»r<c <*•*>*. S* 34« <1MM«H»
Fig. 14. 14C in tree rings (points) vs atmospheric radiocarbon records (lines) at similar latitudes. Bars represent the magnitude of atmospheric nuclear detonation for 3 month periods. For a review of radiocarbon data from atmospheric and tree-ring samples for the period 1945-1997 AD see Ffua ei al. (1999a&b).
10. CONCLUSIONS
AMS C dating is having a tremendous impact on studies in prehistory thanks to a 1000-fold reduction in sample size. Accurate dating is possible by extracting only the most reliable fraction or by minimising sample contamination. Presently, the age limit is around 45,000 -50,000 BP, with potential for an extension to 60,000 BP. AMS 14C can play an important role in the verification of other dating techniques, such as optically stimulated luminescence and U-series dating, which allow a further extension of the datable time span. Alternative AMS radionuclides with longer half-lives have been considered for archaeological dating but 14C remains a unique chronometer to reconstruct the sequence of prehistoric events.
AKNOWLEDGMENTS
We thank Ewan Lawson, Quan Hua and Cheryl Jones for suggestions and many valuable discussions.
465
REFERENCES
Adovasio J.M. and Pedler, D.R. (1997) Monte Verde and the antiquity of humankind in the Americas, Antiquity 71, 573-580.
Allen J, and Holdaway S. (1995) The contamination of Pleistocene radiocarbon determinations in Australia, Antiquity 69, 101-112.
Arnold J.R. and Libby W.F. (1949) Age determinations by radiocarbon content: checks with samples of known age, Science 110, 678-680.
Bard E., Arnold M., Hamelin B., Tisnerat-Laborde N. and Cabioch G. (1998) Radiocarbon Calibration by Means of Mass Spectrometric 230Th/234U and 14C ages of Corals: An Updated Database Including Samples from Barbados, Mururoa and Tahiti, Radiocarbon 40 (3), 1085-1092.
Bennett C.L., Beukens R.P., Clover M.R., Gove H.E., Lievert R.B., Litherland A.E., Purser K.H. and Sondheim W.E. (1977) Radiocarbon dating using accelerators; negative ions provide the key, Science 198, 508-509.
Bird M.I., Ayliffe L.K., Fifield L.K., Turney C.S.M., Cresswell R.G., Barrows T.T. and David B. (1999) Radiocarbon dating of "old" charcoal using a wet oxidation, stepped-combustion procedure, Radiocarbon 41(2), 127-140.
Bischoff J.L., Ludwig K., Garcia J.F., Carbonell E., Vaquero M., Stafford T.W., Jull A.J.T. (1994) Dating of the Basal Aurignacian sandwich at Abric Romani (Catalunya, Spain) by Radiocarbon and Uranium-series, Journal of Archaeological Science 21, 541-551.
Boaretto E., Berkovits D, Hass M., Hui S.K., Kaufman A., Paul M. and Weiner S. (1999) Dating of prehistoric cave sediments and flints using 10Be and 26Al in quartz from Tabun Cave, Israel, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 176, to be published in Nuclear Instruments and Methods in Physics Research B.
Bonani G., Ivy S., Wolfli W., Broshi M., Carmi I. and Strugnell J. (1992) Radiocarbon Dating of Fourteen Dead Sea Scrolls, Radiocarbon 34 (3), 843-849.
Bronk-Ramsey C. and Hedges R.E.M. (1997), Hybrid ion sources: radiocarbon measurements from microgram to milligram, Nuclear Instruments and Methods in Physics Research B 123, 539-545.
Campbell J., Cole N., Hatte E., Tuniz C. and Watchman A, (1996) Dating of rock surface accretions with Aboriginal paintings and engravings in North Queensland, Tempus 6, 231-239.
466
Chappell, J. (1993) Late Pleistocene coasts and human migrations in the Austral region, Department of Prehistory, Research School of Pacific Studies, The Australian National University, Occasional Papers in Prehistory 21,43-48.
Chen M., Lu X., Li D., Liu Y. and Zhou W. (1999) Mini-cyclotron based accelerator mass spectrometry and real 14C measurements, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 64, to be published in Nuclear Instruments and Methods in Physics Research B.
Clottes J., Chauvet J.M., Brunel-Deschamps E., Hillaire C, Daugas J.-P., Arnold M., Cachier H., Evin J., Fortin P., Oberlin C, Tisnerat N. and Valladas H. (1995) The Palaeolithic paintings of the Chauvet-Pont-D'Arc cave, at Vallon-Pont D'Arc (Ardeche, France): direct and indirect radiocarbon dating, C.R. Acad. Sci. Paris 320, 1133-1140.
Damon P.E., Donahue D.J., Gore B.H., Hatheway A.L., Ml A.J.T., Linick T.W., Sercel P.J., Toolin L.J., Bronk C.R., Hall E.T., Hedges R.E.M., Housley R., Law LA., Perry C, Bonani G., Trumbore S., Wolfli W., Ambers J.C., Bowman S.G.E., Leese M.N. and Tite M.S. (1989) Radiocarbon dating of the Shroud of Turin, Nature 337, 611-615.
David B., Roberts R., Tuniz C, Jones R. and Head J. (1997). New optical and radiocarbon dates from Ngarrabulgan Cave, a Pleistocene archaeological site in Australia: implications for the comparability of time clocks and for the human colonisation of Australia, Antiquity 71, 183.
David B., Tuniz C, Lawson E.M., Hua Q., Jacobsen G.E., Head J. and Rowe M. (1999) New AMS determinations for Chillagoe rock art, Australia, and their implications for Northern Australian prehistory, in: D. Seglie (ed.), NEWS95 - International Rock Art Congress, Proceedings CD ROM, Centra Studi e Museo d'Arte Preistorica, Pinerolo (Italy).
Donahue D.J., Linick T.W. and Jull A.J.T. (1990) Isotope-ratio and background corrections for accelerator mass spectrometry radiocarbon measurements, Radiocarbon 32 (2), 135-142.
Fifield L.K. (1999) Accelerator mass spectrometry and its applications, Rep. Prog. Phys 62, 1223-1274.
Fullagar R.L.K., Price D.M. and Head L.M. (1996) Early human occupation of northern Australia: archaeology and thermoluminescence dating of Jinmium rock-shelter, Northern Territory, Antiquity 70, 751-773.
Gove H.E., (1996) Relic, Icon or Hoax: Carbon Dating the Turin Shroud, Institute of Physics Publishing, London.
Hua Q., Barbetti M., Worbes M., Head J. and Levchenko V.A. (1999a) Review of radiocarbon data from atmospheric and tree-ring samples for the period 1945-1997 AD, IAWA Journal 20 (3), 261-283.
467
Hua Q., Barbetti M., Jacobsen G.E., Zoppi U and Lawson E.M. (1999b) Radiocarbon in annual tree rings from Thailand and Tasmania for the period AD 1952-1975, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 90, to be published in Nuclear Instruments and Methods in Physics Research B.
Hughen K.A., Overpeck J.T., Lehman S.J., Kashgarian M., Southon J.R. and Peterson L.C. (1998) A new 14C calibration data set for the last deglaciation based on marine varves, Radiocarbon 40 (1), 483-494.
Jacobsen G.E., Hua Q., Tarshishi J., Fink D., Hotchkis M.A.C., Lawson E.M., Smith A.M. and Tuniz C. (1997) AMS radiocarbon analysis of microsamples, in: Handbook of The Sixth Australian Archaeometry Conference, 10-13 Februrary 1997, Sydney, Australia, p. 36.
Jull A.J.T., Donahue D.J., Hatheway A.L., Linick T.W. and Toolin LJ. (1986) Production of Graphite Targets by Deposition from CO/H2 for Precision Accelerator 14C Measurements, Radiocarbon 28 (2A), 191-197.
Jull A.J.T., Donahue D.J., Broshi M. and Tov E. (1995) Radiocarbon Dating of Scrolls and Linen Fragments from the Judean Desert, Radiocarbon 37 (1), 11-20.
Kitagawa H. and van der Plicht J. (1998) Atmospheric Radiocarbon Calibration to 45,000 yr B.P.: Late Glacial Fluctuations and Cosmogenic Isotope Production, Science 279, 1187-1191.
Laurencich Minelli L., Miccinelli C. and Animato C. (1995) U documento seicentesco "Historia et Rudimenta Linguae Piruanorum", Studi e Materiali di Storia delle Religioni 61, 363-413.
Laurencich Minelli L., Miccinelli C, Animato C. (1998) Lettera di Francisco de Chaves alia Sacra Cesarea Maesta: un inedito del sec. XVI., Studi e Materiali di Storia delle Religioni 64, 57-91.
Lawson E.M., Elliott G., Fallon J., Fink D., Hotchkis M.A.C., Hua Q., Jacobsen G.E, Lee P., Smith A.M., Tuniz C, Tyler P., Williams A. and Zoppi U. (1999) AMS at ANTARES - the first 10 years, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 49, to be published in Nuclear Instruments and Methods in Physics Research B.
Levchenko V.A., Etheridge D.M., Francey R.J., Trudinger C, Tuniz C, Lawson E.M., Smith A.M., Jacobsen G.E., Hua Q., Hotchkis M.A.C., Fink D., Morgan V. and Head J. (1997) Measurement of the 14CC>2 bomb pulse in firn and ice at Law Dome, Antarctica, Nuclear Instruments and Methods in Physics Research B 123, 290-295.
468
Levin L, Kromer B., Schoch-Fischer H., Brans M., Munich M., Berdau D., Vogel J.C. and Munich K.O. (1994) A14C02 records from two sites in Central Europe, in: Boden T.A., Kaiser D.P., Sepanski R.J. and Stoss F.W. (eds.), Trends 93 - A compendium of data on global change, Carbon Dioxide Information Analysis Centre. Oak Ridge National Laboratory, Oak Ridge, 203-222.
Libby W.F. (1946) Atmospheric Helium Three and radiocarbon from cosmic radiation, The Physical Review 69, 671-672.
Manning M.R. and Melhuish W.H. (1994) A14C02 record from Wellington, in: Boden T.A., Kaiser D.P., Sepanski R.J., and Stoss F.W. (eds.), Trends 93 - A compendium of data oh global change, Carbon Dioxide Information Analysis Centre. Oak Ridge National Laboratory, Oak Ridge, 173-202.
Middleton R., Fink D., Klein J. and Sharma P. (1989) 4ICa concentrations in modern bone and their implications for dating, Radiocarbon 31, 305-310.
Milazzo M., Cicardi C, Mannoni T. and Tuniz C. (1997) Non destructive measurements for characterisation of materials and datation of Corona Ferrea of Monza, in: Handbook of The Sixth Australian Archaeometry Conference, 10-13 Februrary 1997, Sydney, Australia, p. 39.
Muller R.A. (1977) Radioisotope dating with a cyclotron, Science 196, 489-494.
Nelson D.E., Korteling R.G. and Stott W.R. (1977) Carbon-14: direct detection at natural concentrations, Science 198, 507-508.
Nelson D.E., Loy T.H., Vogel J.S. and Southon J.R. (1986) Radiocarbon dating blood residues on prehistoric stone tools, Radiocarbon 28,170-174.
Nelson D.E. (1991) A new method for carbon isotopic analysis of protein, Science 251, 552-554
O'Connor S. (1995) 40,000 years of Aboriginal occupation in the Napier Ranges, Kimberley, W.A., Australian Archaeology 41, 58.
Olsson U.I. (1970) The use of Oxalic acid as a standard, in: Olsson I.U. ed, Radiocarbon variations and absolute chronology, Nobel symposium, 12th Proc, John Wiley & Sons, New York, p 17.
Pettitt, P.B., Bronk-Ramsey C, Hedges R.E.M. and Hodgins G.W.L. (1999) AMS radiocarbon dating at Oxford and its contribution to issues of the extinction of Neanderthals and the spread of Homo sapiens sapiens across Eurasia, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 171, to be published in Nuclear Instruments and Methods in Physics Research B.
469
Phillips F.M., Flinsch ML, Elmore D. and Sharma P. (1997) Maximum ages of the Coa valley (Portugal) engravings measured with Chlorine-36, Antiquity 71, 100-104.
Prinoth-Fornwagner R. and Niklaus Th.R. (1994) The man in the ice: results from radiocarbon dating, Nuclear Instruments and Methods in Physics Research B 92, 282-290.
Purser K.H. (1994) A future AMS / chromatography instrument for biochemical and environmental measurements, Nuclear Instruments and Methods in Physics Research B 92, 201-206.
Renfrew, C. (1973). Before civilisation, the radiocarbon revolution and prehistoric Europe, Jonathan Cape, London.
Roberts R.G., Jones R., Spooner N.A., Head M.J., Murray A.S. and Smith M.A. (1994), The human colonisation of Australia: optical dates of 53,000 and 60,000 years bracket human arrival at the Deaf Adder Gorge (Northern Territory), Quaternary Geochronology 13, 575-583.
Roberts R., Walsh G., Murray A., Olley J., Jones R., Morwood M., Tuniz C, Lawson E., Macphail M., Bowdery D. and Naumann I. (1997) Luminescence dating of rock art and past environments using mud-wasp nests in northern Australia, Nature 387, 696-699.
Roberts R., Bird M., Olley J.,Galbraith R., Lawson E., Laslett G., Yoshida H., Jones R. Fullagar R., Jacobsen G. and Hua Q. (1998) Optical and radiocarbon dating at Jinmium rock shelter in northern Australia, Nature 393, 358-362.
Russ J., Hyman M., Shafer H.J. and Rowe M.W. (1990) Radiocarbon dating of prehistoric rock paintings by selective oxidation of organic carbon, Nature 348, 710-7:11.
Stringer C.B. (1986) Direct dates for the fossil hominid record, in: Archaeological results from accelerator dating (ed. Gowlett J.A.J, and Hedges R.E.M.), Oxford University Committee for Archaeology Monogr. Ser. no. 11, 45-50.
Stafford T.W., Hare P.E., Currie L., Jull A.J.T. and Donahue, D. (1990) Accuracy of north American human skeleton ages, Quaternary Research 34, 111-120.
Stuiver M. and Polach H.A. (1977) Discussion: reporting of 14C data, Radiocarbon 19 (3), 355-363.
Stuiver M. (1983) International Agreements and the Use of the New Oxalic Acid Standards, Radiocarbon 25 (2), 793-797,
Stuiver M., Reimer PL. Bard E., Beck J.W., Burr G.S., Hughen K.A., Kromer B., McCormac G., van der Plicht J. and Spurk M. (1998a) INTCAL98 radiocarbon age calibration, 24,000-0 cal BP, Radiocarbon 40 (3), 1041-1083.
470
Stuiver M., Reimer P.J. and Braziunas Th.F. (1998b) High-Precision Radiocarbon Age Calibration for Terrestrial and Marine Samples, Radiocarbon 40 (3), 1127-1152.
Suter M. (1999) Tandem AMS at sub-MeV energies - status and prospects, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 59, to be published in Nuclear Instruments and Methods in Physics Research B.
Taylor, R.E. (1987) Dating techniques in archaeology and paleoanthropology, Anal. Chem. 59,317-331.
Terrasi F., Campajola L., Petrazzuolo F., Brondi A., Cipriano A., D'Onofrio M., Hua Q.f Roca V., Romano M., Romoli M., Tuniz C. and Lawson E. (1994) LTtalia Scacchistica 1064, 48-60.
Thorne A., Grün R., Mortimer G., Spooner N.A., Simpson J.J., McCulloch M., Taylor L. and Curnoe D. (1999) Australia's oldest human remains: age of the Lake Mungo 3 skeleton, Journal of Human Evolution 36, 591-612.
Tuniz C, Fink D., Hotchkis M., Jacobsen G. Lawson E., Smith A., Hua Q., Peter D., Lee P., Levehenko V., Bird R., Boldeman J., Barbetti M., Taylor G. and Head J. (1995) The Antares AMS Centre: A Status Report, Radiocarbon 37 (2), 663-674.
Tuniz C, Bird J.R., Fink D. and Herzog G.F. (1998) Accelerator Mass Spectrometry (Ultrasensitive Analysis for Global Science), CRC Press, Boca Raton (Florida),
Turney C.S.M., Bird M.I. Fifield L.K., Roberts R.G., Smith M.A., Dortch C.E., Grün R., Lawson E., Miller G.H., Dortch J., Cresswell R.G and Ayliffe L.K. (2000) Breaking the radiocarbon barrier and early human occupation at Devil's Lair, southwestern Australia, submitted for publication to Nature.
Valladas H., Cachier H., Maurice P., Bernaldo de Quiros F., Clottes J., Cabrera Valdez V., Uzquiano P., Arnold M. (1992) Direct radiocarbon dates for prehistoric paintings at the Altamira, El Castillo and Niaux Caves, Nature 357, 68-69.
Wachman A.L., Walsh GL., Morwood M.J. and Tuniz, C. (1997) AMS radiocarbon age estimates for early rock paintings in the Kimberley, N.W. Australia: preliminary results, Rock Art Research 14, 18-26.
Wild E., Golser R., Hille P., Kutschera W., Priller A., Puchegger S., Rom W., Steier P. and Vycudilik W. (1998) First 14C Results from Archaeological and Forensic Studies at the Vienna Environmental Research Accelerator, Radiocarbon 40(1), 273-282.
471
Zilhao J. (1995) The age of the Coa valley (Portugal) rock art; validation of archaeological dating to the Palaeolithic and refutation of 'scientific' dating to historic or proto-historic times, Antiquity 69, 883-901.
Zoppi U., Hua Q., Jacobsen G., Lawson E.M., Sarkissian G., Petitti P., Vargiu R. and Laurencich Minelli L. (1999) Controversies in European history: two significant examples, in: Conference Compendium of the 8th International Conference on Accelerator Mass Spectrometry, 6-10 September 1999, Vienna, p. 173, to be published in Nuclear Instruments and Methods in Physics Research B.