An atomic species is defined by two whole numbers: the number of protons in the nucleus (known as Z, or atomic number) and the total number of protons plus neutrons (known as Z, or mass number).
Isotopes are the atoms in an element that have the same atomic number but a different atomic mass; that is, the same number of protons and thus identical chemical properties, but different numbers of neutrons and consequently different physical properties. Isotopes can be stable or unstable or radioisotopes. In the latter, their nuclei have a special property: they emit energy in the form of ionizing radiation while searching for a more stable configuration.
Isotopes are the atoms in an element that have the same atomic number but a different atomic mass
Atomic number (Z) and mass number (A)
The atomic number defines the chemical element that the atom belongs to. Thus, regardless of the number of neutrons they have, all atoms whose nuclei have one proton are hydrogen atoms. All of those with eight protons are oxygen atoms, etcetera.
The mass number is the whole number that is closest to the mass (expressed in atomic mass units) of the atom in question. Thus, all the atoms with A = 2 have a mass of approximately 2 mass units; atoms with A = 235 have a mass of approximately 235 atomic mass units.
Annotation: AZX (where X is the atom’s element)
Isotopes (from the Greek isos = same and tópos = place) are atoms from a same element, whose nuclei have a different number of neutrons and, therefore, differ in mass. That is, they have the same atomic number (Z) but different mass numbers (A).
For instance, carbon is presented in nature as a mix of three isotopes with mass numbers 12, 13 and 14: 12C, 13C and 14C. The global amounts of carbon in each are respectively 98.99%, 1.11% and traces.
Most chemical elements possess more than one isotope, as is the case of tin, the element with the highest number of stable isotopes. Only 21 elements, like beryllium and sodium, have one single natural isotope.
Types of isotopes:
- Natural: Those naturally found in nature. Examples: hydrogen has three natural isotopes (protio, which has no neutrons, deuterium, with one neutron, and tritium, with two). Another element containing very important isotopes is carbon, which includes carbon 12, the referential base of atomic mass in any element; carbon 13, the only carbon with magnetic properties, and radioactive carbon 14, very important since its average life span is 5,730 years and is widely used in archeology to determine the age of organic fossils.
- Artificial: These isotopes, manufactured in nuclear laboratories by bombarding of subatomic particles, usually have a short life span, mostly due to their unstable nature and radioactivity. Examples: iridium 192, used to verify that pipe welding is hermetically sealed, especially as regards transport pipes for heavy crude oil and fuels. Some isotopes from uranium are also used for nuclear work such as electric generation.
Isotopes are also subdivided into stable isotopes (there are less than 300) and unstable or radioactive isotopes (there are around 1,200). The concept of stability is not exact, since there are almost stable isotopes. That is, for some time they are unstable and become stable or turn into other stable isotopes.
Most chemical elements possess more than one isotope, as is the case of tin, the element with the highest number of stable isotopes
Radioisotope (also known as radisotope)
These are radioactive isotopes, since they have an unstable atomic nucleus (due to the balance between neutrons and protons) and emit energy and particles when it changes to a more stable form. The energy liberated in the form change can be measured with a Geiger counter or with photographic film.
Each radioisotope has a characteristic disintegration or semi-life period. Energy may be liberated mostly in the form of alpha (helium nuclei), beta, (electrons or positrons), or gamma (electromagnetic energy) rays.
Several unstable and artificial radioactive isotopes have medical uses. For instance, a technetium isotope (99mTc) may be used to identify blocked blood vessels. Various natural radioactive isotopes are used to determine chronologies, such as the archeological kind (14C).
Applications of radioisotopes
- Medicine: Diagnosis and treatment of diseases, sterilization of products frequently used in clinical and surgical environments, etc.
- Industry and technology: review of materials and welding in construction, control of productive processes, research, etc.
- Agriculture: Plague control, food conservation, etc.
- Art: restoration of art objects, verification of historic or artistic objects, etc.
- Archeology: Geological event dating, etc.
- Research: Universe, industry, medicine, etc.
- Pharmacology: The study of the metabolism of drugs before they are authorized for public use.