**1. Introduction**

74 Gamma Radiation

Yoshida, N. & H. Tsukahara (1987) A γ-ray spectral survey on giant clam colonies using the

w/English abstract).

submersible Shinkai2000. *JAMSTEC J. Deep Sea Res.,* Vol.3, pp.105-112 (in Japanese

We are all exposed to ionizing radiation from natural sources at all times. This radiation is called natural background radiation. Background radiation is the radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources. Natural radioactivity is wide spread in the earth's environment; it exists in soil, plants, water and air. Exposure of radiation mainly come from natural radiation (85 %). The assessment of gamma radiation doses from natural sources is of particular importance because natural radiation is the largest contributor of external dose to the world population (UNSCEAR,2000; Narayana N. et al.,2007) The exposure of human beings to ionizing radiation from natural sources is a continuing and feature of life on earth inescapable (UNSCEAR Report 2000). Throughout the history of life on earth, organisms have been continuosly exposed to radiations from radionuclides produced by cosmic ray interaction in the atmosphere and radiations from naturally occuring substances that are spatially distributed in all living and non-living components of the biosphere.(Whicker F.W. And Schultz, 1982)

Environmental natural gamma radiation is formed from terrestrial and cosmic sources (Merdanoglu and Altinsoy, 2006, M.Degerlier et al., 2008) It comes from two primary sources: cosmic radiation and terrestrial sources. The worldwide average background dose for a human being is about 2.4 millisievert (mSv) per year. This exposure is mostly from cosmic radiation and natural radionuclides in the environment (including those within the body).

The main sources of natural background radiation are radioactive substances in the earth's crust, emanation of radioactive gas from the earth ,cosmic rays from outer space which bombard the earth, trace amounts of radioactivity in the body.

Sources in the Earth include sources in water, soil and food which are incorporated to the human body, to building materials, and to products that incorporate radioactive sources from nature, sources from outer space are the radiation produced by the atomic bombardment of the upper atmosphere by high-energy cosmic rays and sources in the atmosphere, such as the radon gas released from the Earth's crust, which then decays into radioactive atoms that attach to airborne dust, and other particulate (granular, powder) materials.

Gamma Dose Rates of Natural Radioactivity in Adana Region in Turkey 77

On the ground, cosmic radiation makes up on average about 17 % of the natural background radiation to which we are all exposed. The rest consists of radon gas (50%), radiation from

Some radioactive materials - most of which are naturally occurring elements - are actually air pollutants. All of them, as a whole, are a relatively small proportion of the many elements and chemicals that are considered air pollution. Radon is the most significant of these elements, but most radon exposure stems from the indoor environment. Improving technology continues to minimize man-made radioactive air pollutants and monitor air

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

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

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

radiation dose to individuals in typical situations both outdoors and indoors.

region depends on soil and geographic structure.

minerals in the soil (20 %), and radiation in our bodies from food and water (13 %).

quality.

**2. Terrestrial** 

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



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

On the ground, cosmic radiation makes up on average about 17 % of the natural background radiation to which we are all exposed. The rest consists of radon gas (50%), radiation from minerals in the soil (20 %), and radiation in our bodies from food and water (13 %).

Some radioactive materials - most of which are naturally occurring elements - are actually air pollutants. All of them, as a whole, are a relatively small proportion of the many elements and chemicals that are considered air pollution. Radon is the most significant of these elements, but most radon exposure stems from the indoor environment. Improving technology continues to minimize man-made radioactive air pollutants and monitor air quality.
