Radioactivity is defined as the emission of particles and electromagnetic rays from the nucleus of an unstable atom. Six types of radiation produced during nuclear decay were presented within this chapter and include:
- alpha (α) decay which is composed of two protons and two neutrons and has a +2 charge.
- beta (β) decay which is an electron ejected from the nucleus (not from the shells of electrons about the nucleus) and has a -1 charge and no mass. Within the nucleus a neutron emits the electron and is converted into a proton in the process.
- gamma (γ) decay which is characterized by the emission of ionizing radiation and does not contain mass or charge.
- positron (β+) emission which is a positron ejected from the nucleus and has a +1 charge and no mass. Within the nucleus a proton emits the positron and is converted into a neutron in the process.
- electron capture occurs when an inner shell electron combines with a proton and is converted into a neutron. The loss of an inner shell electron leaves a vacancy that will be filled by one of the outer electrons. As the outer electron drops into the vacancy, it will emit energy often in the form of X-rays.
- nuclear fission occurs when an atomic nucleus breaks apart into smaller pieces in a radioactive process that releases excess neutrons.
Each radioactive nuclide has a characteristic, constant half-life (t1/2), the time required for half of the atoms in a sample to decay. The equation below can be used to determine how much isotope will remain after the passage of a given number of half-lives
Radioactive emissions can cause damage to biological systems by causing the breakdown of proteins and DNA. This can lead to cellular and genetic damage and increase a person’s risk for diseases like cancer. However, when used is small quantities and in controlled settings, radioactive tracers and treatments have proven to be revolutionary for the medical field. For example, Radiation therapy is the use of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing. Radioactive tracers have also been very useful in evaluating heart disease, thyroid dysfunction, and other blood disorders. Positron emission tomography (PET) scans use radiation to diagnose and track health conditions and monitor medical treatments by revealing how parts of a patient’s body function and X-rays have long been used to visualize breaks in bones and cavities in teeth.