PROMPT GAMMA ACTIVATION ANALYSIS OF NEOLITHIC GREENSCHIST POLISHED STONE TOOLS

Kasztovszky Zsolt-Szakmány György

Budapest

The neolithic greenschist tools had been widely spread in the Carpathian Basin. In the Alp-Carpathian Region this rock type can be found only in the Alps and in the Southern part of the West Carpathian Mountains. Besides other provenances, greenschist neolithic tools were found in Bicske, Endrőd, Bajc, Zengővárkony and the Northern slope of Mecsek hills (Mucsfa, Györe). The greenschist, as a raw material was very popular among the neolithic people, because it is well processable but durable.

Macroscopically, greenschist has dark green, greyish-green colour, with very fine grain size. The rock consists of lighter and darker stripes of 0.1 mm with black, purple-black spots of 2-3 mm. According to the polarization microscopic investigations, the found greenschist objects are relatively uniform petrographically, but some fine textural differencies can be observed, thus we were able to distinguish two groups of the samples.

Ten greenschist samples - six of them are neolithic tools from the above mentioned location, and four of them are rocks from outcrops (Felsőcsatár, Burg, Bazin) - were investigated with prompt gamma activation analysis at the PGAA system of the Budapest Research Reactor. The average chemical composition of the samples were determined in a volume of about 2x2x2 cm3.

Prompt gamma activation analysis is based on the detectation of prompt gamma photons of 100 keV-11 MeV energy, which are originated from the radiative capture of neutrons into nuclei, or (n,() reaction. The gamma lines are characteristic for a given element, the intensity of them are proportional to the concentration of the element. The method is suitable for determination of all the elements, with different sensitivities. In addition, the PGAA method is absolutely non-destructive and does not require any sample preparation.

Comparing the results of different analytical methods, PGAA measurements gave reliable data for main components (SiO2, Al2O3, FeOt MnO, CaO, MgO, Na2O, and K2O) and some trace elements (Sc, V, Cr, Co, Ni, Sm, Eu, Gd and Dy). For other elements, which are used for characterization of basic rocks (Ta, Nb, Zr, La, Lu, etc.), the present sensitivity of PGAA is not high enough. After the putting into the operation of the "Cold Neutron Source", the sensitivities will improve with a factor of about 100.

According to the petrographical and PGAA results, the investigated samples can be classified into different groups. Some of the neolithic stone tools are similar to the Felsőcsatár and Burg rock samples, and the others are a little bit different from them. Based on the REE-concentrations, the Bazin sample is different from the others.