Dr. Vinaya Kumar Jha
Radiation carries energy which comes from a source and travels through some material or through medium or through space. In Physics, radiation means an electromagnetic (EM) waves which carry energy or moving subatomic particles, especially high-energy particles which cause ionization. The kinds of radiation are electromagnetic wave (like light) and particulate (i.e., mass given off with the energy in motion). Gamma radiation and X-rays, ultraviolet, visible light, infra-red are examples of electromagnetic radiation. Beta particles and alpha particles are examples of particulate radiation. Stream of charged particles reaches to the Earth along with the light and heat radiation from the Sun. Charged particle beyond the solar system also come onto the Earth which is called Cosmic radiation. Sources of particle radiation onto the earth are ionizing radiation can also be produced by devices such as X-ray machines. Low-frequency EM waves or radiation like light wave, infrared and radio wave are not nocuous to biological cells whereas high frequencies EM waves like gamma rays, X rays, UV rays along with highly energetic subatomic particles give adverse effect to living cells and become the cause of disease like cancer. In this report, we discuss the radiations which are present in our environment and harms to human beings through long exposure to these radiations
Environmental radiation is such radiation which surrounds us all the times, in another word, it is ubiquitous. It is also known as background level of radiation in the natural environment. Background radiation has shown constant association with us since the birth of the Earth and development of life on it. Background radiation comprises radiation coming from space, from natural and man-made radionuclides present in space and on the Earth.
Sources of Background Radiation
Background radiation present on the Earth is obtained from both natural and artificial radioactive substances. Some naturally occurring radionuclide like Radon is found in the earth beneath our feet, while others are produced in the atmosphere by radiation from space. Man-made (artificial) radionuclides have come into the environment from activities such as medical procedures that use radionuclides to image the body and nuclear power plant that uses radioactive Uranium as fuel. Persons are continuously irradiated by sources outside and inside their bodies. Outside sources include cosmic radiation and terrestrial radiation. Inside sources include the radioactive molecules that enter our bodies through food and water people consume and the air they breathe in. Whatever its origin, radiation is present everywhere in the environment. Humans on the earth surface receive radiation mainly in three ways, viz.: (1) radiation from space, (2) terrestrial radiation and (3) radiation from radionuclides in the body.
Radiation from Space: Cosmic rays are radiation that enters the Earth’s atmosphere from outside of the solar system and even beyond the Milky Way galaxy. Cosmic rays from beyond the solar system have enough energy to generate additional radiation as they pass through Earth’s atmosphere, creating either radionuclide in the air or secondary particles. Some secondary particles reach the Earth’s surface, most readily near the Earth’s magnetic poles where shielding by the Earth’s magnetic field is the weakest and at high altitudes where the Earth’s atmosphere is the thinnest. Radionuclides created by space radiation (or Cosmic rays) are called cosmogenic radionuclides. They include Tritium (1H3), Beryllium (4Be7), Carbon (6C14) and Sodium (11Na22) etc.
Terrestrial Radiation: Radiation that originates on surface of the Earth is called terrestrial radiation. Ancient radionuclides that were present when the Earth formed about 4.5 billion years ago are found in igneous and sedimentary rock of the Earth’s crust. From the exposed weathered rocks, these radionuclides migrate into soil, water, and even air. In the past, once nuclear weapons were used that also contributed to terrestrial radiation.
Radionuclides in the Body: Terrestrial and cosmogenic radionuclides enter the body through the food and water we take in, and air we breathe in. Radionuclides present inside the body are used and eliminated out of the body during normal metabolism. Other radionuclides decay more slowly and may concentrate in specific body tissues (such as Radium in bone); others are not readily absorbed by the gut and are quickly eliminated. The percentage distribution of radiation from different sources into the environment is presented in Figure 1.
Dose from Background Radiation
A person receives a radiation dose from exposure to radiation sources outside the body (e.g., external radiation from uranium in concrete of the building) and inside the body (e.g., internal radiation from radioactive Potassium absorbed by the cells from the eaten food). Here, the term “dose” means the effective dose, which describes the amount of radiation energy absorbed by the body. The Sievert (Sv) is the unit of dose or smaller unit is microsievert or µSv. Another unit of dose is the gray (Gy) and one trillionth of a gray (nanogray or nGy). For normal people, the annual average total dose from background radiation should be in the order of a few mSv for safe range. Whereas medical technician (radiologist) receives more annual dose than normal people. A radiologist uses proper lead garment (apron) in order to reduce the radiation exposure to the body during the operation of equipment. Dosimeter is a small device kept within the lead apron in order to estimate the radiation dose received by the body while handling the radiation equipment.
Health Effects of Background Radiation
Exposure of body part to high levels of radiation is known to cause cancer. But, the effects on human health from very low doses of radiation (like doses from background radiation) are very difficult to determine because there are so many other factors that shadow the effects of radiation. For example, among people exposed to high Radon levels, cigarette smokers are much more likely to get lung cancer than nonsmokers. Sciences have suggested that there may be some risk of cancer even at the very low doses of background radiation, but the risk is small. Although the overall risk is low for all cancers, but it is not zero and it is greater for some types of cancer than others.
- Environmental Protection Agency. Monitoring for environmental radiation. Available at: http://www.epa.gov/ rpdweb00/rert/monitoring.html. Accessed 1 September 2009.
- FERMILAB radiological control manual, Environmental Radiation Monitoring and Control Revised: December 2007.