Page 14 - Curriculum Visions Dynamic Book

Background radiation
Radioactivity is a fundamental part of the Universe, and therefore we should expect to find natural radiation on Earth. In fact we experience radiation from a variety
of sources as a normal part of our lives. Together, radiation from these sources makes up “background radiation”.
The levels of background radiation have been increased by about one-fifth because of human activities this century, although the vast majority of background radiation is still from natural sources. A few people are more at risk than others from background radiation, especially those living in houses built above rocks rich in radium and from which radon gas seeps to the surface.
Cosmic radiation
This is a term for all the forms of radiation that reach the Earth from other parts of the Universe, including the Sun and all other stars.
Victor Franz Hess, an Austrian physicist, was the first person to prove that radiation continually reached the Earth from space. He received the Nobel Prize in 1936 for this discovery.
Hess made measurements in balloons
that showed that the amount of radiation increased with height. At the height an aircraft travels, the radiation is several times that on the Earth’s surface. This means that frequent aeroplane flyers are slightly more exposed to radiation than those who never fly.
Most cosmic rays are protons, but there are also alpha and beta particles. Cosmic radiation can be of the order of 1 particle/sq cm/second.
 Radon gas is most concentrated over igneous rocks such as granite.
Radioactive carbon dioxide
Cosmic rays bombard all the gases in the upper atmosphere. One effect is to change nitrogen-14 to carbon-14, the radioactive isotope of carbon. When carbon-14 and oxygen combine in the upper air, they produce radioactive carbon dioxide. Some of this is absorbed by plants and can be used to determine their age (see page 19).
 This pie chart shows the main sources of radiation.
Natural background radiation from the ground (about 37%)
Radon (32%)
Internal (body) (17%)
Thoron (5%)
Medical (11.5%)
Radiation from man-made sources is dominated by X-rays and fallout from nuclear reactors (about 13%).
14
14