Sources of Radiation

There are two types of sources of radiationnatural and artificial.

Natural Sources of Radiation

Natural sources of radiation are the sun and other stars and naturally radioactive elements. The sun and other stars release both electromagnetic and particle radiation.

Radiation from the stars results from the fusion of hydrogen nuclei in the stars. The hydrogen changes into helium and gives off a large amount of energy. This produces electromagnetic radiation across the entire spectrum. Besides visible light, a star releases everything from radio waves to high-energy gamma radiation.

Stars also produce alpha and beta particles, protons, neutrons, and other forms of particle radiation. They release high-energy particles called cosmic rays. Solar flare is a phenomenon where the sun releases cosmic rays strong enough to disrupt communications on Earth.

The sources of particle radiation are naturally radioactive substances such as radium, uranium, and many other heavy elements that are found in rocks and soil. However, scientists are capable of creating radioactive forms of any element in a laboratory.

Most naturally radioactive substances belong to one of three sequences of change, which are called radioactive decay seriesi) the uranium series, ii) the thorium series, and iii) the actinium series. Heavy isotopes which are forms of the same element but have different numbers of neutrons decay into various lighter isotopes in each of these series by giving off radiation till they become stable.

The uranium series starts with uranium 238. It is the heaviest isotope of uranium. It has 92 protons and 146 neutrons. After losing an alpha particle, the nucleus has 90 protons and 144 neutrons. It no longer remains uranium, but becomes a radioactive isotope of thorium. This process of changing from one into another element is called transmutation. The thorium breaks down in several steps to radium 226. The radium 226 again decays into radon. Radon is a naturally occurring radioactive gas. Radon might turn hazardous if it accumulates in certain buildings, especially where ventilation is poor. The series continues till the isotope becomes a stable form of lead.

The thorium series starts with thorium 232, an isotope of thorium. It also ends with lead.

The actinium series begins with uranium 235, which is another isotope of uranium. It is also called U-235. Like the other two series, the actinium series continues until the isotope becomes a stable form of lead.

There is another group of naturally radioactive substances, which includes a wide variety of materials that do not belong to a radioactive series. Many of these elements, such as carbon 14, potassium 40, and samarium 146, are produced when cosmic radiation strikes Earth's atmosphere.

Artificial Sources of Radiation

Artificial radioactive substances are formed by human activities, such as the fission that takes place in nuclear weapons and nuclear reactors, or in laboratories. When fission breaks up a nucleus, it releases several types of radiation, including neutrons, gamma radiation, and beta particles. The process also creates new radioactive atoms called fission products. In the 1950s and 1960s, atomic bomb tests produced a new fission product called cesium 137, which was a radioactive isotope of cesium. Nuclear plants also create new radioactive elements. These elements are known as activation products. The pipes and other materials in a nuclear reactor absorb neutrons and other types of radiation and become radioactive. These are then called activation products. Used fuel from nuclear plants also contains fission products like plutonium 239, strontium 90, and barium 140. This used fuel, called nuclear waste, remains radioactive and potentially harmful for many years.

Sometimes physicists use powerful devices to speed up the movement of electrically charged particles that include the entire nuclei. Then physicists shoot stable, non-radioactive atoms with beams of these high-speed particles. This results in collisions producing new radioactive atoms.