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The Science of Nuclear Radiation

posted Nov 8, 2012, 8:39 AM by Administrator NLA   [ updated Nov 15, 2012, 10:36 PM ]
Dr Jaiby Joseph Ajish*

(Dr Joseph Ajish is a Knowledge Contributor to the Nuclear Law Association)

Radiation is energy that comes from a source and travels through space. They are ubiquitous in the environment, and are able to penetrate various materials. Radiation is generated through natural nuclear reactions such as cosmic rays, lightening and supernova explosion or through artificial sources such as high-energy particle accelerators. Radiation can be ionizing or non-ionizing. Ionizing radiation alters chemical bonds in a material to make them chemically reactive and removes electrons from atoms and produces ions. Thus, exposure to ionizing radiation causes damage to living tissues, and it presents a health hazard. Ionizing radiation includes cosmic rays, X-rays, alpha, beta, and gamma rays. In general, any charged particle moving at relativistic speeds (those which travel close to the speed of light) are considered ionizing. Ionizing radiation includes some portion of the ultraviolet spectrum, depending on context. Radio waves, microwaves, infrared light, and visible light are normally considered non-ionizing, although very high intensity beams of these radiations can produce sufficient heat to exhibit some properties of ionizing radiation. Ionizing radiation is invisible and not directly detectable by human senses, so instruments such as Geiger counters are usually required to detect its presence. Biological damage of the radiation can result in sickness, mutilation, cancer and death but it has many practical uses in medicine, research, construction, and in other areas.

Atoms with unstable nuclei are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass as radiation (e.g. Alpha (α), Beta (β), Gamma (γ), neutrons (n)). In general, if the characteristic energy of the radiation is greater than the ionization energy (energy needed to break free an electron of the atom) of the target material, then each particle collision can be expected to ionize or alter a target atom, no matter how low the power of the beam. But most targets are composed of a variety of atoms, which will have a range of ionization energies. Alpha (α) radiation consists of a fast-moving helium nucleus and can be stopped by a sheet of paper. Beta (β) radiation consists of electrons and can be halted by an aluminum plate. Gamma (γ) radiation, consisting of energetic photons is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons that are blocked using light elements, like hydrogen, which can slow down and/or capture them.

Radioactive wastes are usually byproducts of nuclear power generation and other applications of nuclear technology such as nuclear weapons reprocessing. Radioactive waste is regulated by government agencies in order to protect health and the environment. The radioactivity of all nuclear waste diminishes with time. Current major approaches to managing radioactive waste have been deep burial or nuclear transmutation for the long-lasting, high-level wastes. For low-level waste, it is typically isolated and stored for a period until it no longer poses a hazard. Low-level waste with low levels of radioactivity such as common medical or industrial radioactive wastes are needed to be stored for only hours or days, while high-level wastes such as spent nuclear fuel must be stored for years. The time frame in question when dealing with radioactive waste ranges from 10,000 to 1,000,000 years.

The amount of high-level waste worldwide is currently increasing by about 12,000 metric tons every year. The cost of managing and disposing of nuclear power plant wastes represents about 5% of the total cost of the electricity generated. Governments around the world are considering a range of waste management and disposal options, though there has been limited progress toward long-term waste management solutions.

Nuclear reactors produce large quantities of ionizing radiation as a byproduct of fission. In addition, they also produce highly radioactive nuclear waste, which contains radioactive material and will emit ionizing radiation for thousands of years for some of the fission byproducts. The safe disposal of this waste is critical to protect future generations from radiation exposure. However, it is currently imperfect and remains as a highly controversial issue. During normal conditions, radioactive emissions from nuclear power plants are generally lower than coal-burning plants; though several high profile nuclear accidents such as Chernobyl and Fukushima have released dangerous levels of radioactivity.

A comparative radiation chart (sourced) is placed below to better understand radiation dose from different sources.

*Dr Jaiby Joseph Ajish, is an Experimental Nuclear Physicist, and holds a Ph.D from Kent State University, Ohio, USA. She works with the STAR Collaboration in analyzing the data from particle collisions at Brookhaven National Lab’s Relativistic Heavy Ion Collider (RHIC). She has about five years of experience in nuclear research including two years of detector R&D work at Brookhaven National Lab, New York.