RADIO ISOTOPES

Radionuclide or Radioisotopes Isotopes - Atoms with same number of protons but a different number of neutrons in the nucleus An additional neutron or two may upset the binding energy and cause the atom to become unstable. In an unstable atom, the nucleus changes by giving off a neutron to get back to a balanced state. As the unstable nucleus changes, it gives off radiation and is said to be radioactive. Radioisotopes are isotopes that are unstable and release radiation. All isotopes are not radioisotopes.

ISOTOPES

Transmutation All elements with atomic numbers > 83 are radioisotopes Elements with atomic numbers < 83, have isotopes and most have at least one radioisotope. As a radioisotope tries to stabilize, it may transform into a new element in a process called transmutation. Nucleus of radioisotopes is characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron (internal conversion). Radioisotope thus undergoes radioactive decay, and emits a gamma rays (s) and/or subatomic particles. These particles constitute ionizing radiation. Radioisotopes occur naturally, and can also be artificially produced.

Radioactive decay Alpha particles result from the decay of relatively heavy radioisotopes. They consist of two neutrons and two protons, bound together. Americium 241 (Am-241) is a example, commonly found in household smoke detectors.

In beta decay, a neutron converts to a proton emitting a beta particle in the process. Beta particle is identical to an ordinary electron. Carbon-14 (C-14) is a radioisotope of carbon, which undergoes beta decay and is used to establish the age of ancient artifacts ("carbon dating").

Gamma rays are emitted if a nucleus still has excess energy following decay and the emission of other particles. They are electromagnetic in nature (called photons), with a discrete, unique energy This is used to identify different radioisotopes. Gamma rays are not physical particles, but their interactions with matter are described by assigning them particle-like properties.

Naturally occurring radionuclides Primordial radionuclides: Originate mainly from the interiors of stars. Their half-lives are so long - not yet decayed. Secondary radionuclides: Radiogenic isotopes derived from the decay of primordial radionuclides. Shorter half-lives than primordial radionuclides. Cosmogenic radionuclides: Carbon-14 - continually formed in the atmosphere due to cosmic rays.

Artificially produced radionuclides Nuclear reactors: Produced with nuclear reactors. Neutrons activate elements placed within the reactor. Eg. Thallium-201 and iridium-192 Particle accelerators: Cyclotrons accelerate protons at a target to produce positron emitting radioisotopes e.g. fluorine-18. Radionuclide generators: Contain a parent isotope that decays to produce a radioisotope. Parent is produced in a nuclear reactor – molybdenum-99. Nuclear explosions: Produced as an unavoidable side effect of nuclear and thermonuclear explosions.

Uses For their chemical properties Carbon can serve as tracers because they are chemically very similar to the non-radioactive nuclides. Result examined with a radiation detector, such as a Geiger counter For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive.

2. As sources of radiation: Used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays or positrons can provide diagnostic information about a person's internal anatomy and the functioning of specific organs. This is used in some forms of tomography: single photon emission computed tomography and positron emission tomography scanning.

Medicines - promising method of treatment in hemopoietic forms of tumors. Gamma sources sterilize syringes and other medical equipment. In biochemistry and genetics, radionuclides label molecules allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport. In food preservation, radiation is used to stop the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables. In agriculture and animal husbandry, radionuclides produce high quality crops, disease and weather resistant varieties of crops, to study how fertilisers and insecticides work, and to improve the production and health of domestic animals.

In industry and mining, radionuclides examine welds, to detect leaks, to study the rate of wear, erosion and corrosion of metals, and for on-stream analysis of a wide range of minerals and fuels. Most household smoke detectors contain the radionuclide americium formed in nuclear reactors, saving many lives. Radionuclides trace and analyze pollutants, to study the movement of surface water, and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers. Natural radionuclides are used in geology, archeology, and paleontology to measure ages of rocks, minerals, and fossil materials.

Dangers If radionuclides are released into the environment, through accident, poor disposal, or other means, they can potentially cause harmful effects of radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways applied to living beings. This is called radiation poisoning. Radionuclides can also cause malfunction of some electrical devices.