Page 42 - PR 2014 2016 07 Nuclear Science and Technology

184 Nuclear Science and Technology | Progress Report

production centers, trade route identification, and one of each reference material are packed
raw material, object exchange, time scale, and in aluminum foil and irradiated in the research
prehistoric people mobility patterns. This in- reactor swimming pool, IEA-R1, from IPEN-
formation is possible because differences in CNEN/SP at a thermal neutron flux of about
chemical composition are typically interpreted 8.92 x 10 cm s for 8 h. Arsenic, Ba, K, La, Lu,
12
-2 -1
as evidence for different production locations. Na, Nd, Sm, and Yb are measured after a 7-day
cooling time and Ce, Cr, Cs, Eu, Fe, Hf, Rb, Sb,
In our laboratory, the Archaeometric Studies Sc, Tb, Th, Zn and U after 3 or 4 weeks’ time.
Group of the IPEN-CNEN/SP is working with a
research program as a means of physical and By means of XRD, it is possible to determine
chemical characterization of ceramic from the mineralogical composition in the ceram-
several regions of the country. The researchers ics, i.e., it indicates the relative proportions of
are inserted in an archaeometric program at minerals in the sample. The chemical and the
Activation Analysis Laboratory – LAN – and are mineralogical compositions of the ceramics are
focused on identifying the behavioural factors both complementary and equally important in
that affect chemical variability. The group use determining its properties. Both are necessary
several analytical techniques, like instrumen- to understand the history and properties of
tal neutron activation analysis, INAA, X-ray the material being investigated.
diffraction, XRD, thermoluminescence dating,
electron paramagnetic resonance, among other The firing temperature and dating is being
answering questions like “why?”, “where”? used in our Group by means of electron para-
and “when”? in studies of the natural and magnetic resonance and thermoluminescence
man-made objects. There is no doubt that if an to found the firing and the age of ceramic ma-
artifact is held in hand, its age and authenticity terials found at archaeological sites.
is of utmost interest. The most classical dating
methodology is based on seriation, stylistic The quartz and feldspar grains found in pieces
technique, clay and pigment. However, these of pottery or other types of fired clay acted as
approaches may reveal which objects belong dosimeters, i.e., they were able to record the
together, but not their age in a quantitative amount of radiation to which they had been
manner. exposed. In the case of pottery, this radiation
dose was that received by the grains since the
A typical procedure used in our laboratory time when they had been heated. The heat-
consist in cleaning the ceramics` outer surface ing erased the previous TL signal and with
and drilling using a tungsten carbide rotary file it the information on the previous radiation
attached to the end of a flexible shaft, variable exposure, i.e., that related to the time elapsed
speed drill. After that, this material is dried since the minerals had been formed. The age
in an oven at 105°C for 24h and stored in a calculation in luminescence requires the es-
desiccator. timation of two factors: the equivalent dose
(De) which is the absorbed dose, generally
For INAA, approximately 100 mg of ceramic expressed in Gy (1Gy = 1J) and measured in
samples, the standard reference materials a luminescence reader, and the annual dose
NIST-SRM-1633b and IAEA-Soil-7, are (Dan), which is the received dose of ionizing
weighed in polyethylene bags and wrapped radiation rate, expressed in mGy/year or Gy/
in aluminum foil. Groups of 8 to 10 samples ka. The ratio between both doses, De / Dan,

Instituto de Pesquisas Energéticas e Nucleares