Isotopic Constitution of Tellurium, Silicon, Tungsten, Molybdenum, and Bromine

The relative abundances of the isotopes of tellurium, silicon, tungsten, molybdenum, and bromine have been redetermined by means of a mass spectrograph of the Nier type. The results are as follows: Tellurium. Samples in the form of tellurium hexafluoride were employed and the ions TeF₅⁺ and TeF₃⁺ were used in measuring relative abundances. The existence of isotope 120 was confirmed. With the assumption of a packing fraction of -4, the above values for relative abundance lead to a value of 127.64±{}0.01 for the chemical atomic weight. Silicon. Samples in the form of silicon tetrafluoride were employed and the ions SiF₄⁺ and SiF₃⁺ were used. The results are as follows: With Aston's values for the isotopic weights, the above values for isotopic abundances give 28.086 for the chemical atomic weight. Tungsten. The isotopic constitution of tungsten has been re-investigated with a view to obtaining more exact data on relative abundance. Relative isotopic abundances were measured for the W⁺ ion obtained by electronic bombardment of tungsten hexacarbonyl vapor. The existence of isotope 180 has been confirmed. The estimates of isotopic abundances obtained by electrometrical methods are: On the basis of a packing fraction of +2, these estimates lead to a value of 183.88 for the chemical atomic weight. Molybdenum. The isotopic constitution of molybdenum has been re-investigated. The values for isotopic abundance as determined electro-metrically from Mo⁺ and Mo⁺⁺ ions produced by electronic bombardment of molybdenum hexacarbonyl are: These values are in closer agreement with values reported by Valley than with values obtained by Aston or Mattauch. Bromine. Values for the relative abundance of the bromine isotopes have been obtained from measurements on Br₂⁺, Br⁺, and Br⁺⁺ ions formed by electronic bombardment of bromine vapor. The relative abundances are in essential agreement with the values reported by Blewett: No new isotopes of bromine were observed.