U and Th contents of samples and soils were determined by an alpha spectrometry system (Oasis, Oxford) with a passive ion-implanted silicon detector (active area
300 mm2, background 3.6 counts per day and the minimum depletion thickness of 100 μm).
The lower limit ofdetection of the method used was 0.4 Bq kg-1 of dry weight.
The radioactive element K of samples and soils was determined by atomic absorption spectrometry.
The dose rates are presented in Table 2, where the internal contribution was calculated from alpha and beta activity measurements coming from the samples taking into account the alpha correction factor.
To estimate the alpha attenuation factor (a-value) for each site we applied additive
alpha dose technique (the procedures are the same as
additive beta dose) using an 241Am alpha source for new
disks. By taking the ratio (beta ED/alpha ED) we estimated
the a-value (Aitken, 1985).
The a-values for each site are presented in Table 2. The external contribution was
calculated from gamma activity coming from the soil.
The dose rate conversion factor of alpha, beta and gamma has been done according to Aitken (1985) and the cosmic dose rate was assumed to be 0.15 Gy/ka according to (Aitken, 1985) as the level (depth) from which the pottery were collected was less than one meter below the present earth surface.
Finally the calculated age before present (BP), by applying Eq. 1.1, of the sherds from each site are presented in Table 1.
The errors for the age determination, were calculated using the error propagation rules.
The sixth column presents the mean age for each site with standard deviation (SD).