Page 191 - 00. Complete Version - Progress Report IPEN 2014-2016

Nuclear Science and Technology | Progress Report 191

annual dose rate coming from the radioactive Pleistocene–Holocene South American mega-
elements present in the soil and in the sample fauna belonging to different faunistic mo-
itself can be calculated by determining the U, ments related to climate changes during the
Th and K concentration. Therefore, the deter- quaternary. The equivalent dose (De) was de-
mination of the dose rate depends on the con- termined using single exponential fitting re-
centration of these main radioactive elements. sulting in (24±1) Gy. The De was converted to
age using ROSY ESR Dating program and the
Neutron Activation Analysis has the sensitiv- concentration of radioisotopes present in the
ity and the accuracy necessary to determine sample and soil determined through neutron
U and Th with this objective. Depending on activation analysis. The ages cover the range
the composition of the sample, the determi- of 25–34 ka. This information is important
nation of U and Th can be improved irradiat- to contextualize other findings in the region
ing the sample inside a Cd capsule, reducing from different sites and to help obtain bet-
the thermal neutron incidence on the sample ter information about the climate changes in
and, therefore, diminishing the activation of this region. (Partnership: Universidade Sagra-
possible interfering nuclides. do Coração, Bauru, SP, Brazil; Departamento de
Física, Faculdade de Filosofia Ciências e Letras,
Electron spin resonance (ESR) dating was ap- USP, Ribeirão Preto, SP, Brazil).
plied to a Smilodon populator tooth found in
“Toca de Cima dos Pilão”, located in the sur- Relative INAA and k0-INAA at
roundings of the Serra da Capivara National IPEN: a Comparative Study
Park. Neutron Activation Analysis was used to
determine the concentration of radioisotopes The Neutron Activation Analysis Laboratory at
present in the sample and in the sediment to IPEN (LAN-IPEN) has been analyzing different
calculate the internal and external dose rates. kinds of samples for decades, using the relative
The result of age found is 93±9 ka, which con- method of instrumental neutron activation
firmed the presence of this species in Serra da analysis (INAA) at the IEA-R1 nuclear research
Capivara National Park in the late Pleistocene. reactor of IPEN. In this method, samples and
standards are irradiated simultaneously with
Electron spin resonance (ESR) dating was ap- neutrons under the same conditions. Elemen-
plied to a fossil human tooth and shell found tal concentrations are calculated by compar-
at the archaeological site Toca do Enoque lo- ison of the activities of the gamma-rays from
cated in Serra das Confusões National Park (Pi- the sample and standard. This procedure re-
auí, Brazil). The ages for the tooth and the shell quires the preparation of element standards,
(~4.8 kyBP) agreed with C-14 dating of the shell which is very laborious and time consum-
and other samples (charcoal) collected at the ing. Furthermore, some elements present in
same study site, showing the validity of ESR the sample cannot be analyzed due to the ab-
dating for this range of ages. sence of a corresponding element standard.
The k0-INAA method, developed by the Insti-
Electron spin resonance (ESR) dating was ap- tute of Nuclear Sciences, Gent, Belgium, has
plied to date a sample of fossil tooth found in been increasingly used, as it requires only a
Ribeira Valley, São Paulo, Brazil. This region is single comparator such as 197Au for multiele-
characterized by abundant fossil records of mental determination instead of multielemen-