**4. Materials and methods**

In order to determine the outdoor gamma dose rates region and activity concentrations in soil samples is divided to 6 basic geographic areas in Adana region in Turkey. Each geographic area called as a sampling station. This region is located in the southern part of Turkey.

The outdoor gamma dose rates were measured by Eberline smart portable device (ESP-2) connected with and SPA-6 model plastic scintillation detector. Measurements were taken in air for two minutes at 1 m above the ground and the gamma dose rates were recorded as µRh-1 . The gamma absorbed doses in nGy h-1 were also converted to annual effective dose in mSv y-1 as proposed by UNSCEAR .

SPA-6's calibration was done using 137Cs with an electrometer device for certain distances in the laboratory.

Sampling stations were chosen uncultivated and near to populated areas to understand the amount of dose received by the population because of absorbed gamma dose rate in air. At

Gamma Dose Rates of Natural Radioactivity in Adana Region in Turkey 81

The outdoor gamma dose rates was shown in Table 2 and Figure 8.The average outdoor gamma dose rates in air is 76.2 nGy h-1. The highest value was measured as 134 nGy h-1 in Feke town. The lowest outdoor gamma dose rate was measured as 49.5 nGy h-1 in Karatas town.

U-238 series Th-232 Series Pb-214 Bi-214 Ac-228 Tl-208

(Yuregir) 5.80 4.83 8.38 8.36

(Center) 22.59 21.34 39.38 43.47

(Center) 17.38 16.77 16.15 14.98

(Center) 9.10 9.75 8.65 8.37

(Center) 28.33 23.06 49.87 54.89

Table 2. Activity concentrations in soil samples as Bq kg-1

17.66 16.17 23.63 27.19

Fig. 3. Typical Gamma Ray Spectrum

Balcali Fen Edebiyat Fakultesi

Yeniyayla

Feke

Ceyhan

Karatas

Saimbeyli

each measurement a reading was taken in air for 1 h at 1 m above the ground level. The instrument calculates an average 1 h exposure rate based on the multiple measurement results. The results include both terrestrial and cosmic ray components of gamma radiation level that was recorded in units of µRh-1.

Soil samples were taken with 25 cm diameter cores collected at different locations and different depths ranging from 0 to 30 cm. These samples were taken from uncultivated fields and sampling stations were chosen close to populated areas.

The soil samples were dried, pulverized, homogenized and sieved through 2 mm mesh. The meshed soil samples were transferred to Marinelli beakers of 1000 ml capacity. The soil samples were weighed, carefully sealed and stored for 30 days to allow secular equilibrium between thorium and radium and their products (Mollah et al., 1987)

Gamma spectropic measurements were performed using a coaxial HPGe detector having a 16 % relative efficiency. A detection system containing a Canberra Model 2020 Amplifier and a Canberra S-85 Multi Channel Analyzer with Model 8087 4K ADC was used for the measurements. The detector was shielded in a 10 cm thick lead well, internally lined with 2 mm thick copper and 2 mm thick cadmium foils. The overall detector resolution (FWHM) of 1,9 keV was obtained for the 1332 keV gamma line of 60Co. Energy calibration and relative efficiency calibration of the gamma spectrometer were carried out using 109Cd, 57Co, 113Sn, 134Cs, 137Cs, 188Y and 60Co calibration sources in 1000 ml Marinelli beaker covering the energy range from 80 to 2500 keV. The counting time for each sample, as well as for background was 50,000 s.

Gamma spectroscopy was used to determine the activities of 238U, 232Th, 40K and 137Cs. For concentrations of 232Th and 238U the following gamma transition lines were used; 232Th series: 228Ac (911 keV), 208Tl (583.1keV); 238U series : 214Pb(351.9 keV) and 214Bi (609.2 keV).

The contribution of natural radionuclides to the absorbed dose rate in air depends on the concentration of the radionuclides in soil. The largest part of the gamma radiation comes from terrestrial radionuclides. There is a direct correlation between terrestrial gamma radiation and radionuclide concentration in soil.
