Radon and Other Sources of Background Radiation

Uranium-239 has a half-life of 23.5 min and decays spontaneously to the element neptunium hy the emission of heta particles  

Neptunium is also unstable, with a half-life of 2.33 days it converts into a second new element, plutonium (Pu)  

Plutonium-239, like neptunium-239, is radioactive, hut it has a half-life of 24,100 years. Because of the relative values of the half-Uves, very little neptunium could he accumulated, hut the plutonium could he obtained in larger quantities. The names of neptunium and plutonium were taken from the mythological names Neptune and Pluto in the same atomic number sequence as the order of the planets Uranus (uranium), Neptune, and Pluto out from the Sun. 

By 1996, elements up to 112 had all been created, many with extremely short half-lives. Element 112, for example, has a half-life of 240 microseconds. 

Four atoms each of element 113 and element 115 were produced in a fusion reaction between calcium-48 and americium-243 in 2004. These two elements, combined with element 114, produced earher, extend the periodic table to 115 elements. Element 113 was produced by the alpha decay of element 115. 

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