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Promethium (Pm)
Promethium (Pm)
Element 61 on the periodic table. This radioactive metal is one
of the rare-earth metals and a lanthanide. It was discovered in 1947 by J. A. Marinsky, L. E. Glendenin and C. D. Coryell.
Protactinium (Pa)
Element 91 on the periodic table. A radioactive chemical element of the actinide series.
It was discovered in 1913 by Kasimir Fajans and O.H. Göhring.
Proton
A positively charged particle in the nucleus of an atom that balances out the charge of the surrounding electrons.
R
Radiation
The exchange of energy with the surroundings by means of particles of energy.
Radiation – This diagram shows the main sources of background radiation that most of us experience.
Radioactive
Emitting radiation or particles from the nucleus of atoms. (See also: Radioactive decay.)
Radioactive decay
A change in a radioactive element due to loss of mass through radiation. For example, uranium decays (or changes) to lead. (See also: Half-life.)
Radioisotope
A shortened version of the phrase radioactive isotope.
Radium (Ra)
Element 88 on the periodic table. This silvery-white metal is the heaviest radioactive element in group 2 (the alkaline-earth metals).
Radium was discovered in 1889 by Pierre Curie, Marie Curie and G. Bémon.
Radium found an important use in medicine as a way of treating cancer by focusing radiation on tumours. In recent times it has been replaced by cobalt-60.
Radium glows in the dark and was mixed with zinc sulphide to make luminous paint. This stopped when the dangers of using radium were recognised.
Radon (Rn)
Element 86 on the periodic table. A heavy radioactive gas of
group 8 (the noble gases).
It is produced by the radioactive decay of radium.
Radon is a colourless, odourless, tasteless gas. The atmosphere contains small amounts of radon, especially above rocks like granite as a result of seepage from the radioactive decay of uranium in these rocks. High levels of radon gas may be a health hazard.
Rare-earth metal, rare-earth element
An element belonging to a series of 17 chemically similar metals also known as lanthanides on the periodic table.
They are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lutetium(Lu), lanthanum (La), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).
Reaction
The combination of two substances using parts of each to produce
new substances. For example, the reactants sodium chloride and sulphuric acid react and combine to produce sodium sulphate, chlorine and water. (See also: Catalyst.)
Reactivity, reactive
The tendency for a substance to react with other substances. The term is most widely used in comparing the reactivity of metals.
Radon (32%)
Gamma radiation (19%)
Cosmic radiation (14%)
Medical (11.5%)
Fallout (0.5%) Miscellaneous (0.5%)
Occupational (0.4%)
Nuclear discharges (0.1%)
Internal (body) (17%)
Thoron (5%)
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