Aplicação da Tomografia Computadorizada 3D com Raios X Microfoco no exame de Peças Arqueológicas

Transcription

1 Nuclear Instrumentation Laboratory Aplicação da Tomografia Computadorizada 3D com Raios X Microfoco no exame de Peças Arqueológicas R.T.Lopes, S.M.F. Mendonça de Souza, L.F. Oliveira and E.F.O. de Jesus Fundação Oswaldo Cruz, ENSP e Museu Nacional/UFRJ

2 Computed Tomography: Transversal Section - CT gives a image digital of a transversal section of um phantom.

3 Evolução das imagens

4 Representação do sistema de tomografia

5 Representação do sistema de tomografia

6 Reconstrução 3D a partir de projeções 2D obtidas por feixe cônico corpo de prova detetor 2D fonte de raios-x

7 Visualização 3D

8

9 Visualização 3D

10 Visualização 3D

11 Aplicação da Tomografia 3D na calota de Lagoa Santa (a) frente, (b) lado direito and (c) parte inferior (a) (c) (b)

12 Imagem Radiográfica

13 Projeções da amostra

14 Imagens Reconstruídas

15 Arqueometria Aplicação na Arqueologia

16 Arqueometria Aplicação na Arqueologia

17 Arqueometria Aplicação na Arqueologia

18 Aplicação na Arqueologia Arqueometria

19 Aplicação na Arqueologia PLANO XY

20 Aplicação na Arqueologia PLANO XZ

21 Aplicação na Arqueologia PLANO YZ

22 Nuclear Instrumentation Laboratory Elemental Characterization of a Fossilized Cap from Lagoa Santa-Brazil Using Non- Destructive EDXRF Analysis X-Ray Spectrometry ; 34: University of Rio de Janeiro State - Physics Institute Fundação Oswaldo Cruz, ENSP and National Museum/UFRJ

23 Objective The main objective of this work is to use the EDXRF technique, associated with statistical tests, in the study of a fossilized cap from Lagoa Santa in Brazil. The scientific document produced here also has two goals: first it will certainly help to erase any illusion about the nature of this finding; second, and once more, it will help us to understand the nature of scientific knowledge and its fakes. The choice of non-destructive analysis took in account the interest in keeping intact this historical object.

24 Introduction The energy dispersive X-ray Fluorescence spectrometry (EDXRF) is a multi-elemental and non-destructive analytical technique that can be applied to many areas of science and technology. Besides it should be a non-destructive technique to preserve the integrity (physical and chemical) of the studied object and consequently to maintain its historical and cultural value. A skullcap found in 1975, among fossilized bones in Harold Walter s paleontological collection from Lagoa Santa Brazilian limestone caves has been suggested to be a possible proof of the existence of archaic morphologies in South America.

25 Introduction - continuated The described condition of extreme fossilization of Lagoa Santa calotte, suggested it was different from the other human remains from Lagoa Santa, reinforcing the hypothesis of its great antiquity. The physical anthropologists, geologists and archeologists from National Museum in Rio de Janeiro, Brazil who examined the object in the seventies, have proposed that the calotte was a fake. Brazilian professionals had the opinion that it was just a replica. The recent interest for the prehistoric Brazilian collections of great antiquity, forced also a review of this cap, in order to publish its detailed description that allowed demonstrating it is real nature and scientific value.

26 Materials and Methods The analysis of a polemic Calotte The calotte has been registered in the Section of Biological Anthropology of National Museum, under the registration number of The calotte consists of nearly complete frontal bone, and major portions of bath parietals. The measurements of the cap are 160mm of maximum length along the sagital axis, and 120mm of maximum width perpendicular to it. Its thickness, excluding the suppraorbital area, is around 9mm.

27 The experimental setup The EDXRF system employed a mini X-ray tube with W anode (30 kev and 75 µa). Fluorescent radiation is detected with a 30mm 2 detector (180 ev resolution at Mn-K α line). Si(Li) The X-ray beam is filtered through a Ti filter. The angle of incident x-ray beam is 16 degree to the sample surface. The detector was placed perpendicular to the sample surface. The x-ray fluoresce spectra were evaluated with software package QXAS/IAEA.

28 Schematic layout of the EDXRF spectrometer Detector Si(Li) X-ray Tube ψ 16 0 Calotte

29 Materials and Methods - continuated The cap did not receive any special pre-treatment before the measures. The integrity of the cap was analyzed taking place a radiographic exam of the piece. It was observed marks due to restoration. Therefore, it was decided, for a better analysis, that the cap would be divided in seven parts following the restoration marks. The measures of X-ray fluorescence were carried on in each one of the parts of the piece.

30 (a) radiographic exam of de cap (b) the cap divided in seven parts for study (a) restoration marks (b)

31 Statistic tests Materials and Methods - continuated Correlation test: Methods of correlation analysis will be applied starting from the elementary concentrations in several points of the cap so that it is tested the hypothesis that different parts of the cap possess weak correlation, indicating evidences that the cap can have been mounted with different materials. ANOVA test: Methodology to compare the average arithmetic of the groups. Tukey test: To examine, simultaneously, multiple comparisons between all the pairs of groups of averages

32 Results and Discussion The spectra of XRF for each one of the parts of the cap are enough similar (the same chemical composition). The presence of 13 elements is observed in different amounts: Major elements: Ca, Fe and Sr. Minor elements: Mn, Zn, Pb. Trace elements: S, K, Ti, Cu, Br, Rb and Zr. It is not possible to elaborate, concretely, any conclusion in according to the differences between the seven parts of the cap starting from the analysis of the fluorescence spectra.

33 Typical XRF spectra of various parts of calotte. relative counts S K Ca Mn Ti Fe Cu Zn Pb Br Rb Zr Sr part energy (kev)

34 Table 1 - Ca/Sr concentration in the cap, rock and bones of the same archaeological site. Sample part part part part part part part part part a 5b 5c 6 7 rock b Ca/Sr No inference can be made in relation to similarity between the different parts of the cap starting from Ca/Sr values Does some linear relation exist between the different parts of the cap? It is coherent to admit the existence of a linear relation supposing that the whole cap is constituted of materials of same origin.

35 Table 2 - Results of the correlation test. Part a 5b 5c 6 7 rock a b c Strong correlation exists between all the parts of the cap and the rock sample. Medium correlation coefficients the parts 5a, 5b and 5c present distinctions. rock Are these significant differences to affirm that the cap is a fake piece? Are those differences the expected results of statistical floatation?

36 Table 3 - Results of the ANOVA test Source of Variation SQ gl MQ F p-value F critic Between Groups Inside of the Groups Total E E E E There are evidences that the medium values of the correlation coefficients present significant differences. This test intensifies the hypothesis that the cap is fake. To determine exactly that part or parts of the cap are different, we should make all the possible comparisons in pairs between the various parts of the cap.

37 The result of the analysis using the test of Tukey a 5a 5b 5b 5c 5c rock rock a 5b 5c 6 7 rock 36 groups of data (correlation coefficients), generating 422 pairs (degrees of freedom) that were compared with the critical interval of the test. Parts 5a, 5b and 5c presented significant differences between each average pair. The applied statistical tests reinforce the hypothesis that the parts 5a, 5b and 5c (supraorbital ridges and glabela) had been mounted with from different origins.

38 Conclusions Ca/Sr in different parts of the calotte reinforce the hypothesis that the cap had been mounted with pieces from different origins, as suspected from the appearance of the fractured borders. Coefficient of correlation calculated based on EDXRF and Tukey test confirmed weak correlation between the supraorbital ridges and glabela of the cap and the rest of them. The anatomical details were modeled to suggest an archaic human cap.

39 Conclusions - continued The data and documents presented here demonstrate that the cap is a composed object, made of mended fossil fragments, probably animal bones, masked by a crust or mass simulating sand grains cemented by limestone calcium salts. The fake has been built with anatomical knowledge. It is carefully finished, a good imitation, prepared to attend any purpose that is far from the interest of our discussion.