ESR response in tooth enamel to high-resolution CT scanning
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ORIGINAL PAPER
ESR response in tooth enamel to high-resolution CT scanning Rainer Grün & Sheela Athreya & Rachna Raj & Rajeev Patnaik
Received: 28 January 2011 / Accepted: 20 September 2011 / Published online: 11 November 2011 # Springer-Verlag 2011
Abstract High-resolution CT scanning of teeth with a resolution on the 20 to 30 μm scale introduces doses in the range of 250 to 420 Gy in the tooth enamel. If the induced doses cannot be precisely estimated, subsequent ESR dating analysis becomes impossible. Considering the increased availability of portable, high-resolution CT scanners, curators of valuable human dental fossils have to make an informed decision whether they want to preclude ESR analysis, one of the few dating methods that can be applied to older fossils. Keywords Computed tomography . Tooth enamel . ESR dating
Introduction With the increasing availability of computed tomography (CT) scanners, more and more human fossils are scanned with high resolution (e.g., Wu and Schepartz 2009). This is of great benefit to palaeoanthropological research, as the CT R. Grün (*) Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia e-mail: [email protected] S. Athreya Department of Anthropology, Texas A&M University, College Station, TX 77843, USA R. Raj Department of Geology, Maharaja Sayajirao University of Baroda, Vadodara, Gujarat 390 010, India R. Patnaik Centre for Petroleum and Applied Geology, Panjab University, Chandigarh 160 014, India
scanner provides objective data that can be used by all scholars in the same way, thus alleviating the need for subjective measurements. For CT scanning, an X-ray generator is used. CT scanning of living organisms, particularly humans, is limited by health and safety regulations. Except for cancer treatment, typical CT generated doses are in the range of 1 to 20 mGy. For vital organs, the doses are kept to a feasible minimum. For example, the head may receive around 1.5 mGy (Shrimpton and Edyvean 1998), while other areas of the body may receive doses of up to 20 mGy (Brenner and Hall 2007). Doses on such scales are usually negligible in ESR dating studies, where archaeological doses in the range from a few to thousands of grays are estimated. Even a lethal dose of around 5 Gy will often be within the error range of ESR dose estimations. However, human fossils are obtained from individuals that are already dead, and no such restrictions apply. On the positive side, scans with extreme resolution can be obtained, as for example by Smith et al. (2007) who could reconstruct the enamel growth rate of the Irhoud hominid. On the negative side, samples may receive doses, which make subsequent ESR dating impossible. This study is the consequence of trying to date the relatively recent site Rampura, Gujarat, in western India. The specimen was discovered as an individual burial along the lower Narmada River (Athreya and Raj 2010). The exposed sediments at Rampura are of alluvial fan facies of the S1 surface; thermoluminescence dating
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