Natural radiation in the environment comes from two sources: cosmic rays and radiation present in the earth crust. Cosmic rays have already been discussed in 'Air Travel and Cosmic Radiation' of the column 'Radiation Tidbits' in e-Bulletin on Educational Resources. This article focuses on radiation present in the earth crust.
Naturally-occurring radiation has been part of the earth since the latter came into existence. Such primordial radiation existing in the earth crust diffuses slowly into air, water and the body of living organisms (animals and plants). As it cannot be felt or sensed by human beings, it was not until about a hundred years ago when scientists began to invent measuring instruments and discovered the existence of radiation.
Written by: Yeung Siu-wai
Naturally-occurring radiation exists everywhere in nature