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    Gadolinium

    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    152Gd 151.919 80(2)0.0020(3)
    154Gd 153.920 87(2)0.0218(2)
    155Gd 154.922 63(2)0.1480(9)
    156Gd 155.922 13(2)0.2047(3)
    157Gd 156.923 97(2)0.1565(4)
    158Gd 157.924 11(2)0.2484(8)
    160Gd 159.927 06(2)0.2186(3)

    In 1969, the Commission recommended the atomic weight of gadolinium to be Ar(Gd) = 157.25(3) based on recent mass-spectrometric determinations. It has remained unchanged since that time.

    152Gd has a very long half-life in excess of 1014 a. Within the life time of the earth, this radioactivity will not have affected the atomic weight to the precision here quoted. The "g" notation arises from the presence of naturally occurring fission products found in fossil reactors at Gabon, south-west Africa.

    SOURCE  Atomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
    © IUPAC 2003

    CIAAW

    Gadolinium
    Ar(Gd) = 157.25(3) since 1969

    The name derives from the mineral gadolinite, in which it was found, and that had been named for the Finnish rare earth chemist Johan Gadolin. Gadolinium was discovered by the Swiss chemist Jean-Charles Galissard de Marignac in 1886, who produced a white oxide in a samarskite mineral. In 1886, the French chemist Paul-Emile Lecoq de Boisbaudran gave the name gadolinium.