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DEFINITIONS/ INFORMATION FOR NUCLEAR CHEMISTRY. RADIOACTIVITY – The “spontaneous” emission of particles and/or radiation from certain types of “unstable” nuclei.
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RADIOACTIVITY – The “spontaneous” emission of particles and/or radiation from certain types of “unstable” nuclei. Ernest Rutherford was a major investigator in studying natural forms or radioactivity. Uranium and thorium were among the elements he studied noticing unusual characteristics that set them apart from stable isotopes. His studies were a key factor in determining the existence of alpha (a) and beta (b) particles. He helped establish this new field of chemistry along with Frenchman Paul Villard who later discovered gamma (g) radiation.
ALPHA (a) EMISSION – Alpha particles are helium nuclei comprised of 2 protons and 2 neutrons with a charge of + 2. This means that the mass number is equal to “4” and the atomic number is equal to “2.” These are massive particles compared to most other types of radiation. Proportionally they are 7500 times the mass of an electron. External penetration is relatively low with little shielding required an literally no damage sustained.
BETA (b) EMISSION – Beta particles are electrons, usually emitted in streams with the mass and charge of an electron (-1). Within the nucleus of the source a neutron is converted to a proton. Tritium forming an isotope of helium is a good example. The nuclear transformation consists of a neutron being converted to a proton in the nucleus of the source. External penetration is usually in the ballpark of 1 cm of living tissue causing such damage as skin burns/cancer. Plexiglas, tin foil or 100 sheets of paper provides adequate shielding.
GAMMA (g) EMISSION– This is pure energy in the form of radiation similar to X-rays. Gamma rays have no mass and are not particles. Since their frequency is higher than X-rays they have more energy than X-rays. External penetration is extensive and severe resulting in maximum damage usually in the bone marrow where leukemia can develop. Lead is required for shielding. Bone is “not” a form of shielding for protection from this type of radioactive emission.
POSITRON EMISSION – Positrons are positive electrons with the same mass as an electron and a positive charge of +1. The nuclear transformation consists of a proton being converted to a neutron in the nucleus of the source. Positrons were discovered by Carl Anderson in 1932. They are considered to be the antimatter analogue to an electron. Polonium-207 is a radioisotope that undergoes this type of transition to form bismuth-207.
NEUTRON EMISSION – Neutrons are a form of radiation that have mass similar to a proton and no charge. When struck by neutrons matter becomes radioactive due to the increase in neutron/proton ratio. Since neutrons are considerably more massive than electrons (Remember CHE 101!) much more shielding is required and permanent damage is caused.
ELECTRON CAPTURE – Electron capture or K-capture occurs when an extranuclear electron is captured by a nucleus. Similar, but not identical to positron emission, the nuclear transformation consists of a proton being converted to a neutron in the nucleus of the source. The reason it is sometimes referred to as K-capture is because in the old nomenclature the innermost electron shell was called the K shell. Beryllium-7 can undergo this type of transformation to form lithium-7.
BOMBARDMENT REACTION – A bombardment reaction is initiated by striking a very large, massive nucleus with a small stable atom. This is not fusion! It usually results in a man-made element which lasts only for a short time before breaking down.
BINDING ENERGY – The energy required or necessary (endergonic) to completely break down a nucleus into individual protons and neutrons. Binding energy is considered to be a measure of the stability of an atom. The “Binding Energy” chart or plot graphs binding energy per nucleon versus mass number of an element. What we see is a sharp increase from the very small elements like hydrogen and helium to a curve for the moderate size elements including iron to a gradual decline to the very large elements like uranium. Iron(Fe) possesses the highest binding energy of any element. This represents the greatest nuclear stability on the periodic chart.
FISSION – The breakdown of a “large unstable” nucleus into two or more “unstable” nuclei of intermediate mass resulting in an extremely large release of energy according to “e = mc2!” The loss of mass must equal the amount of energy released. Atomic bombs and nuclear power plants are examples of fission. The United States currently operates 103 nuclear power plants including the one in Clinton, Illinois. There are 435 total nuclear power plants spread throughout the world.
FUSION – The combination of two or more “light stable” nuclei into one “heavier stable” nucleus. Much more energy is released than in fission. Hydrogen bombs and stars are examples of fusion. Once achieved matter takes the form of a “plasma.” Nuclear fusion is “not” used as a source of power or energy for the general public yet because it is impractical. Research in this field is continuing with high hopes that it will eventually produce inexpensive energy since hydrogen is a relatively cheap fuel for this reaction. The high cost of research as well as the dangers involved have prevented progress thus far.
