Short Primer on U238 Radioactive Decay

Short Primer U238 Decay

SHORT PRIMER ON RADIOACTIVE DECAY URANIUM 238 (U238)
Atoms in a radioactive substance decay in a random fashion but at a characteristic rate. The length of time this takes, the number of steps required and the kinds of radiation released at each step are well known. The half-life is the time taken for half of the atoms of a radioactive substance to decay. Half-lives can range from less than a millionth of a second to millions of years depending on the element concerned. After one half-life the level of radioactivity of a substance is halved, after two half-lives it is reduced to one quarter, after three half-lives to one-eighth and so on. All uranium atoms are mildly radioactive. The type of radiation given off at each step and the 'half-life' of each step that U-238 goes through in its change into stable, non-radioactive lead-206. The shorter-lived each kind of atom, the more radioactive it is.

The Decay Chain of Radon: Radon originates from Uranium-238 which naturally occurs in most types of granite and soil in varying degrees. The following table for uranium-238 shows the various changes. As it undergoes radioactive decay, a chain of products is formed as a result of one by-product itself decaying to another element, which in turn decays further until finally reaching an element that is stable. In this case that stable element is Lead. The element we're interested in is Radon-222 (there is another form, Radon-218, but the half-life of this isotope is only a few hundredths of a second, so it is less of a problem). This is produced roughly halfway down this decay chain from Radium-226. Radon is a particular problem because it is a gas, and as such can leave the surrounding rock and enter buildings along with atmospheric air.

Radon-222

Half-life : 3.825 days - Emissions: Alpha 5.48MeV - Beta None - Gamma None

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