For medical applications (explained in later chapters), we usually need rather short­lived radionuclides that have to be artificially produced because we cannot separate them economically from natural sources. We can produce radioactive materials in the following ways (also see Chapter 8):

• In nuclear reactors, where irradiation channels are formed through the nuclear reactor shield to put the target in the way of high neutron flux. The neutrons induce nuclear transformations.

• The other possibility is to use accelerators, especially cyclotrons, invented by Ernest Lawrence (1901 — 1958) at Berkeley, who was awarded the Nobel Prize in physics in 1939. In 2005, there were about 130 cyclotrons in the European Union, 80% of which were dedicated to routine medical radioisotope production.

• The daughter element of a radionuclide may also be radioactive; this fact is utilized in radioisotope generators (see later in this chapter and Section 8.7.1.4).

From a practical point of view, the most important difference is that radioisotopes produced in nuclear reactors are usually cheaper than cyclotron products. We shall list some other aspects next.