**2. Terrestrial**

76 Gamma Radiation

Radiation UNSCEAR

Air 1.26 0.2-10.0 Internal 0.29 0.2-1.0 Terrestrial 0.48 0.3-1.0 Cosmic 0.39 0.3-1.0 Total 2.40 1.0-13.0

Medical 0.60 0.03-2.0 Fallout 0.007 0-1+ others 0.0052 0-20

(mSv) Typical Range (mSv)

Fig. 1. Exposure radiation dose rates from natural and artificial sources

Type Source World Average

Table 1. Exposure dose rates as mSv from natural and artificial sources in the World

Fig. 2. Exposure dose percentage from natural and artificial radiation sources

Natural

Man Made

Naturally occurring radionuclides of terrestrial origin (also called primordial radionuclides) are present in various degrees in all media in the environment, including the human body itself. Only those radionuclides with half-lives comparable to the age of the earth, and their decay products, exist in significant quantities in these materials. Irradiation of the human body from external sources is mainly by gamma radiation from radionuclides in the 238U and 232Th series and from 40K. These radionuclides are also present in the body and irradiate the various organs with alpha and beta particles, as well as gamma rays. Some other terrestrial radionuclides, including those of the 235U series, 87Rb, 138La, 147Sm and 176Lu exist in nature but at such low levels that their contributions to the dose in humans are small.

Natural radionuclides in soil generate a significant componed of the background radiation exposure of the population (Karahan and Bayulken, 2000) Gamma radiation intensity in a region depends on soil and geographic structure.

External exposures outdoors arise from terrestrial radionuclides present at trace levels in all soils. The specific levels are related to the types of rock from which the soils originate. Higher radiation levels are associated with igneous rocks, such as granite and lower levels with sedimentary rocks. There are exceptions however as some shales and phosphate rocks have relatively high content of radionuclides. There have been many surveys to determine the background levels of radionuclides in soils, which can in turn be related to the absorbed dose rates in air. The latter can easily be measured directly, and these results provide an even more extensive evaluation of the background exposure levels in different countries. All of these spectrometric measurements indicate that the three components of the external radiation field, namely from the gamma emitting radionuclides in the 238U and 232Th series and 40K, make approximately equal contributions to the externally incident gamma radiation dose to individuals in typical situations both outdoors and indoors.

The radionuclides in the uranium and thorium decay chains cannot be assumed to be in radioactive equilibrium. The isotopes 238U and 234U are in approximate equilibrium as they are separated by two much shorter lived nuclides, 234Th and 234Pa. The decay process itself may however allow some dissociation of the decay radionuclide from the source material, facilitating subsequent environmental transfer. Thus, 234U may be somewhat deficient relative to 238U in soils and enhanced in rivers and the sea. The radionuclide 226Ra in this chain may have slightly different concentrations than 238U because separation may occur between its parent 230Th and uranium and because radium has greater mobility in the

Gamma Dose Rates of Natural Radioactivity in Adana Region in Turkey 79

Cosmic radiation observed at a high elevation would be expected to have higher counts as a

The cosmic radiation originates from space as cosmic rays whose contribution to background changes mainly with elevation and latitude. Cosmic radiation consist of energetic charged particles, such as protons and helium ions, moving through space. They originate from events beyond our solar system and from the sun. When these particles enter the Earth's atmosphere they collide with, and disrupt, atoms in our atmosphere, producing secondary, less intense, radiation. By the time cosmic radiation reaches the ground its

The amount, or intensity, of cosmic radiation depends on altitude and latitude, as well as the stage of the solar cycle. The Earth's atmosphere provides considerable protection from cosmic radiation. At commercial aircraft altitudes the protective layer of the Earth's atmosphere is much thinner than it is on the ground and the intensity of cosmic radiation is

The Earth's magnetic field can deflect some of the cosmic radiation away from the Earth. The shielding ability of the magnetic field is most effective over the equator and least effective over the poles. The intensity of cosmic radiation at aircraft altitudes around the

The sun's magnetic field can also deflect cosmic radiation away from the Earth. The strength of the sun's magnetic field varies with the approximate 11 year cycle of rise and decline of solar activity (solar cycle). When solar activity is low (solar minimum), the magnetic field is less effective in deflecting cosmic radiation; cosmic radiation reaching the Earth will be more intense during solar minimum. The effect of solar activity on intensity of cosmic radiation is much smaller than that caused by altitude or latitude. The sun ejects energetic particles, such as protons (solar flares), which may also contribute to the intensity of cosmic radiation. However, only on very infrequent occasions would solar flares have sufficient energy to

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

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

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

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

approximately 100 times greater at these altitudes than it is on the ground.

increase the intensity of cosmic radiation at commercial aircraft altitudes.

result of less atmosphere above the flight line.

intensity has been considerably reduced.

equator is about three times less than at the poles.

**4. Materials and methods** 

in mSv y-1 as proposed by UNSCEAR .

Turkey.

the laboratory.

environment. The decay products of 226Ra include the gaseous element radon, which diffuses out of the soil, reducing the exposure rate from the 238U series. The radon radionuclide in this series 222Rn has a half life of only a few days but it has two longer lived decay products, 210Pb and 210Po, which are important in dose evaluations. For the 232Th series, similar considerations apply. The radionuclide 228Ra has a sufficiently long half-life that may allow some separation from its parent 232Th. The gaseous element of the chain 220Rn has a very short half life and long lived decay products.

The activity concentration of 40K in soil is an order of magnitude higher than that of 238U or 232Th.

Terrestrial radiation is due to various radioactive nuclides that are present in soil, water, air and their abundance changes depending on the geological and geographical features of region (UNSCEAR Report 2000) The intensity of the terrestrial natural radioactivity varies by an order of magnitude for different regions of the world due to geological and environmental factors (Patra A.K.et al, 2006)

The variations in the abundance and distribution of the primordial radionuclides in the environment account for the spatial variations in the natural gamma radioactivity of such environments (Isinkaye M.O, et al., 2008) The terrestrial component is due to the radioactive nuclides that are present in air, soils, rocks, water and building materials in amounts that vary significantly depending on the geological and geografical features of a region.

Radionuclides when released to the atmosphere, undergo decay in transit or are deposited on Earth's surface by wet or dry deposition within relatively short periods. They are initially deposited on the upper surface of the soil, but are quickly weathered into the first few centimeters of the soil (UNSCEAR Report,2000; Isinkaye M.O et al., 2008)

In its first assessment of representative concentrations of these radionuclides in soil, in the UNSCEAR 1982. Committee suggested the values of 370,25 and 25 Bq kg-1 for 40K, 238U and 232Th respectively.

Direct measurements of absorbed dose rates in air have been carried out in the last few decades in many countries of the world.
