Naturally occurring radioactive substances have high nucleon number. It is possible to make artificial radioactive substances by bombarding lighter nuclides withÂ Â - particles, protons or neutrons. The radioactive substances produced in this manner are known as radioisotopes.
A nuclide is any species of atom of which each atom has an identical proton number and also an identical nucleon number. Different nuclides, which have the same proton number (but different nucleon numbers) are called isotopes (isotopic nuclides). The first radioisotope was an unstable isotope of phosphorus. It was produced in 1934 by bombarding aluminium withÂ Â - particles, i.e.,
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We return to sources of radioactivity in this chapter in order to learn about methods which are used to make radioisotopes.
The type of radioisotope of value to nuclear medicine imaging should have characteristics which keep the radiation dose to the patient as low as possible. For this reason they generally have a short half life and emit only gamma-rays - that is no alpha-particle or beta-particle emissions. From an energy point of view the gamma-ray energy should not be so low that the radiation gets completely absorbed before emerging from the patient's body and not too high that it is difficult to detect. For this reason most of the radioisotopes used emit gamma-rays of medium energy, that is between about 100 and 200 keV. Finally since the radioisotope needs to be incorporated into some form of radiopharmaceutical it should also be capable of being produced in a form which is amenable to chemical, pharmaceutical and sterile processing.
The production methods we will consider are nuclear fission, nuclear bombardment and the radioisotope generator.
It was just over a century ago that a little known French scientist named Henri Becquerel came across something new and immensely startling. At the time, while working with phosphorescent materials (i.e. materials that glow in the dark after being subjected to light), he discovered naturally occurring rays that he couldnâ€™t account for. In time, these rays were discovered to be present in several naturally occurring elements, and were dubbed radioactivity. Those metals that exhibited them also came to be known as Radioactive Isotopes.
Radioisotopes, (also known as radioactive isotopes or radionuclides), are atoms with a different number of neutrons than a usual atom. Due to this imbalance, these isotopes have an unstable nucleus that decays, and in the process emitting alpha, beta and gamma rays until the isotope reaches stability. Once itâ€™s stable, the isotope has transformed into another element entirely. Every chemical element has one or more radioisotopes, with over 1,000 isotopes accounted for in total. Approximately 50 of...