**3. Cosmic**

The main contributors to natural radiation are high energy cosmic ray particles incident on the Earth's atmosphere and radioactive nuclides that originated in the Earth's crust. Humans are affected by both external and internal exposures (UNSCEAR Report 2000)

Cosmic radiation is formed due to high energy particles that come from outer space and continually bombard the Earth. These cosmic rays interact with the nuclei in atmosphere, producing a cascade of interactions and secondary reaction products that contribute to cosmic ray exposures. The cosmic ray interactions also produce radioactive nuclei known as cosmogenic radionuclides (UNSCEAR 2000)

Although cosmic radiation increases with increasing altitude, it could be expected that people living at high altitudes suffer more from cosmic rays than those at sea level. Because of the Earth's magnetic field, the cosmic ray intensity varies with latitude, the lowest value being at the geomagnetic equator.

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

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

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

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

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

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

Direct measurements of absorbed dose rates in air have been carried out in the last few

The main contributors to natural radiation are high energy cosmic ray particles incident on the Earth's atmosphere and radioactive nuclides that originated in the Earth's crust. Humans

Cosmic radiation is formed due to high energy particles that come from outer space and continually bombard the Earth. These cosmic rays interact with the nuclei in atmosphere, producing a cascade of interactions and secondary reaction products that contribute to cosmic ray exposures. The cosmic ray interactions also produce radioactive nuclei known as

Although cosmic radiation increases with increasing altitude, it could be expected that people living at high altitudes suffer more from cosmic rays than those at sea level. Because of the Earth's magnetic field, the cosmic ray intensity varies with latitude, the lowest value

are affected by both external and internal exposures (UNSCEAR Report 2000)

vary significantly depending on the geological and geografical features of a region.

centimeters of the soil (UNSCEAR Report,2000; Isinkaye M.O et al., 2008)

220Rn has a very short half life and long lived decay products.

environmental factors (Patra A.K.et al, 2006)

decades in many countries of the world.

cosmogenic radionuclides (UNSCEAR 2000)

being at the geomagnetic equator.

232Th.

232Th respectively.

**3. Cosmic** 

Cosmic radiation observed at a high elevation would be expected to have higher counts as a result of less atmosphere above the flight line.

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 intensity has been considerably reduced.

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

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 equator is about three times less than at the poles.

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 increase the intensity of cosmic radiation at commercial aircraft altitudes.
