ABSTRACT
I n this chapter, we give an overview of the sources of radionuclides found in our environment. Some, such as 238U and 40K occur naturally, while others, such as 137Cs
and 60Co are man-made, and result from industrial or military activities. The first artificial nuclear reaction was performed by Ernest Rutherford in 1917, when
he bombarded stable 14N with α-particles, each reaction creating an 17O nucleus and a proton. However, no radionuclides were produced because 17O is stable. With the discovery of the neutron by James Chadwick in 1932, a number of radionuclides of non-natural origin began to be created. Using neutrons, Enrico Fermi and others attempted to produce elements heavier than uranium using nuclear reactions, but in many of the experiments the radionuclides produced were lighter than uranium, for example, barium. This was explained by Lise Meitner and Otto Frisch in 1938, who showed that bombarding uranium with neutrons caused the uranium nucleus to split into two parts. This process, called nuclear fission, was found to release large amounts of energy, and attempts were made to construct a device for controlled nuclear fission on a larger scale. These attempts proved successful in 1942, when Fermi was able to produce a self-sustaining chain reaction, heralding the start of the nuclear era.
