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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    180Ta 179.947 46(2)0.000 1201(32)
    181Ta 180.948 00(2)0.999 8799(32)

    In 1969, the Commission recommended Ar(Ta) = 180.9479(3) based on new mass-spectrometric measurements, and recognized tantalum as the element whose atomic weight could be stated very precisely because of single predominant isotope, 181Ta (99.99 %). Standard atomic weight of tantalum was last revised in 2005 to Ar(Ta) = 180.947 88(2). Mass discrimination in the isotopic-abundance measurements have a very small effect to the atomic weight of tantalum.

    The minor isotope, 180Ta, is radioactive with a very long half-life of more than 1013 a. It is the last quasi-stable isotope to be discovered. Its interest is heightened by the discovery that it is not the ground-state isomer.

    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(Ta) = 180.947 88(2) since 2005

    The name derives from the Greek mythological character Tantalus who was banished to Hades, the region of lost souls where he was placed up to his chin in water, which receded whenever he tried to drink it, and under branches of fruit, which drew back whenever he tried to pick their fruit. This name was selected because of the insolubility of tantalum in acids; thus, when placed in the midst of acids, it is incapable of taking any of them up. Tantalum was discovered by the Swedish chemist and mineralogist Anders- Gustav Ekeberg in 1802.