Natural Occurring Radionuclide Materials

The stellar material, from which the earth was formed, about 4.5 billion years ago, contained many unstable nuclides (Scholten and Timmermans, 1996). Some of the original primordial nuclides, whose half-lives are about as long as the earth's age, are still present. Radiation comes from outer space (cosmic), the ground terrestrial, and even from within over bodies. It present in the air we breathe, the food we eat, the water we drink and in the construction materials used to build our houses. So, radiation is all around us, it is naturally in our environment and it has been since the birth of our planet (Maher and Raed, 2007). Radioactivity of soil environment is one of the major sources of exposure to human (Abusini, 2007). The 235U, 232Th series and natural 40K are the main source of natural radioactivity in soil (Yasir et al., 2007; Vosniakos et al., 2002). Since these natural occurring radio nuclides materials, (NORMs) such as 238U, 232Th, 235U, and 40K have very long halflives (up to 1010 years), their presence of soils and rocks can simply be considered as permanent. The geological and geographical conditions are the major factors effects, the natural environmental radioactivity and the associated external exposure due to gamma radiation. Thus these radiation levels appear at different levels in the soil of each region in the world (UNSCEAR, 2000). Issue in terms of radiological protection exposure to natural source of radiation becomes an important. In 1992 the national radiological protection Board (NRPB), estimated that radon accounts for approximately 50% of annual dose of radiation from all sources in the most of the world (Ibrahim, 1999). An average person receives a radiation dose of about 300 millirem per year from natural sources compared to a dose of about 50 millirem from produced material source of radioactive materials such as medical x-ray (UNSCEAR, 1988). Exposure of public to radiation from any sources is unlikely. The European committee has issued a draft proposal for revision of the basic safety standards for the protection of workers and the general against the dangers of ionizing radiation (Marcelo and Pedro, 2007). The United Nations Scientific Committee on the Effects of Atomic Radiation established that the world mean dose from natural radiation sources of normal area is estimated to be 2.4 mSv.y-1 while for all manmade sources including exposure, is about 0.8 mSv.y-1 (UNSCEAR, 1993; Valter at el., 2008). Thus 75% of the radiation dose received by humanity is come from natural radiation source. It is clear that the assessment of gamma radiation dose from natural source is of particular importance as natural radiation is the largest contributor to the external dose of the world population (UNSCEAR, 1988).

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