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Module 11: Radioecology in the North. The three types of radiation Identify radiation as a normal part of the environment Define the concept of half-life and nuclear fission Man-made radionuclides and their effects on the environment. Overview.
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Module 11: Radioecology in the North • The three types of radiation • Identify radiation as a normal part of the environment • Define the concept of half-life and nuclear fission • Man-made radionuclides and their effects on the environment
Overview • Awesome energies are locked in the nuclei of atoms (e.g. explosion of first atomic bomb in 1945) • All humankind shares the benefits and danger of atomic energy (a dilemma in itself) • Chernobyl and Amchitka events have left a legacy that the circumpolar North has to deal with • Nuclear energy represents both opportunities (e.g. economic benefit of uranium mining) and challenges (e.g. high radio-activity)
Concepts Chemical Energy • Energy produced (exothermic) or absorbed (endothermic) in the process of a chemical reaction. In such a reaction, energy losses or gains usually involve only the outermost electrons of the atoms (or ions) of the system undergoing change. • Note: A chemical bond is established or broken without disrupting the original atomic or ionic identities of the constituents.
Concepts Nuclear energy • Energy stored in the bonds of the sub-atomic particles in the nuclei of atoms. Such energy can be released through nuclear reaction such as (1) emission of radioactivity, (2) nuclear fission, and (3) nuclear fusion.
Concepts Radioactivity • The phenomenon of an unstable nucleus breaking down and giving off energy-loaded radiation (electromagnetic radiation and sub-atomic particles) • Note: X-rays is a form of radioactivity used in medical imaging (invented by Marie Curie)
Nuclear Chemistry and Radioactivity • Basic building block of matter is the atom • The atom is composed of three basic particles: a proton with a positive charge, an electron with a negative charge, and a neutron with no charge • The protons and neutrons in an atom are located in a very small volume called the nucleus • Each atomic element is characterized by the number of its electrons, its protons, and its neutrons • Many atoms bonded together is called a molecule
Nuclear Chemistry and Radioactivity (cont’d) • Each element has an atomic number equal to its number of protons • Hydrogen, H: has atomic number 1 (1 proton in the nucleus) • Radon, Rn: has atomic number 86 (86 protons in the nucleus) • Atoms of a given element contain the same number of protons, but may contain different numbers of neutrons in the nucleus (i.e. isotopes) protium (0 neutron) H deuterium (1 neutron) tritium (2 neutrons)
Nuclear Chemistry and Radioactivity (cont’d) • Protons and neutrons are held together by forces that are very strong • There are limits to the stability of nuclear forces • Changes of the nucleus from a less stable to a more stable condition always release radioactive emission • Energies of nuclear reactions are 100,000 times as much as those associated with molecular re-arrangements
Radioactivity • Spontaneous disintegration of certain unstable nuclei • Many of these unstable nuclei occur naturally (e.g. each of you is emitting radioactivity right now, due to K isotopes in your body!) • Living organisms receive a “normal” dose of radioactivity from cosmic and terrestrial sources • Primary terrestrial sources include carbon-14, strontium-90, and cesium-37 from uranium and thorium ores
Alpha Decay Reaction (Uranium) (Thorium) (Helium)
Radioactivity (cont’d) • There are 3 types of transformation by which a naturally occurring radioactive nuclei can decay: • Alpha particle (He nuclei) • Beta particle (electrons) • Gamma rays (photons)
Radioactivity (cont’d) • Different nuclei disintegrate, or decay, at different rates • The rate of decay is reflected by the half life of the nuclei (13Cs = 30 years half life, 14C is 5770 years)
Half life 2 x Half life 4 x Half life
Sources of Radioactivity Chernobyl (nuclear accident)
Chernobyl: Radiation Fallout Released one hundred times more radiation than the atom bombs dropped over Hiroshima and Nagasaki
Physics of Radioactivity • Radioactivity emits energy-loaded particles (He nuclei, protons, electrons, neutrons, and photons) • Damages to living tissues relate to how the energy of particles are dissipated • Water, when irradiated, contains H+ and OH- (free radical) ions that are very reactive
Radioactivity: Damages to Tissues • Radiation creates “ions” in our cells and these ions disrupt cell processes • Radiation may alter bio-molecules like DNA (most important), proteins, and lipid cell membranes • Radiation, through DNA dysfunctions, may result in cells becoming tumors
Radioactivity: the Good Parts • The body has the ability to repair radiation damage • Protection against source-radiation can be achieved through the use of barriers (lead, concrete) • Natural sources of radiation are about 300 mrem/year, mostly from radon-222 (a by-product of uranium-238 decay)
Radioactive Contamination(due to man-made radionuclides) (Finland)
Radionuclide Behaviour in Marine Systems • Transport pathways: • Water movements • Precipitation • Sediments from rivers • Marine ecosystems are less vulnerable to atmospheric radiocesium than freshwater and terrestrial systems
