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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    156Dy 155.924 284(8)0.000 56(3)
    158Dy 157.924 41(2)0.000 95(3)
    160Dy 159.925 203(5)0.023 29(18)
    161Dy 160.926 939(5)0.188 89(42)
    162Dy 161.926 804(5)0.254 75(36)
    163Dy 162.928 737(5)0.248 96(42)
    164Dy 163.929 181(5)0.282 60(54)

    In 1969, the Commission assessed Ar(Dy) = 162.50(3). The atomic weight and uncertainty of dysprosium were changed to their current values in 2001 as a result of new mass-spectrometric measurements. 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


    Ar(Dy) = 162.500(1) since 2001

    The name derives from the Greek dysprositos for "hard to get at", owing to the difficulty in separating this rare earth element from a holmium mineral in which it was found. It was discovered by the Swiss chemist Marc Delafontaine in the mineral samarskite in 1878 and called philippia. Philippia was subsequently thought to be a mixture of terbium and yttrium. It was later rediscovered in a holmium sample by the French chemist Paul-Emile Lecoq de Boisbaudran in 1886, who was then credited with the discovery. Dysprosium was first isolated by the French chemist Georges Urbain in 1906.