Biochemical Techniques and Instrumentation

3.1.1. Radioisotopes

The elements that have an equal number of protons and neutrons are most stable. The stable atoms have a binding energy to hold the protons and neutrons together. The isotopes are atoms of the same element that have the same number of protons but a different number of neutrons in the nucleus. If an atom has an additional neutron or two, it may remain stable. Sometimes, an additional neutron or two may upset the binding energy and cause the atom to become unstable. The nucleus then changes by giving off a neutron to get back to a balanced state. When the nucleus loses a neutron, it gives off energy and it is said to be radioactive. Therefore, radioisotopes are isotopes that are unstable and release radiation, when loses a neutron.

All isotopes are not radioisotopes. Radioisotopes are also referred as radionuclides or radioactive isotopes. All elements with atomic numbers greater than 83 are radioisotopes. Elements with atomic numbers of 83 and less, have isotopes with stable nucleus and most have at least one radioisotope with unstable nucleus.

The unstable nucleus is characterized by excess energy which is either imparted to a newly-created radiation particle within the nucleus, or to an atomic electron through internal conversion. This process of transformation into a new element is known as transmutation. The radioisotope during transmutation process undergoes radioactive decay and emits a gamma rays (s) and/or subatomic particles such as alpha and beta rays. These particles constitute ionizing radiation.