Atomic Weight of Cæsium: Use of the Word ‘Mass-spectrograph’


THE first mass-speetra obtained from caesium by means of a hot anode showed only one line of mass number 133. As I pointed out,1 the conditions of the experiment precluded any accuracy of measurement sufficient to decide whether the chemical atomic weight then and since accepted, 132.81, did or did not represent the weight of the atom. Quite recently, K. T. Bainbridge,2 using Dempster's method of analysis, has confirmed the simplicity of caesium to such a degree as to make him confident that no other isotope exists to the extent of 0.3 per cent. As he points out, on this view the atomic weight of 132.81 would imply a packing fraction of -14.3. Such a figure would be so completely abnormal that it seemed desirable that it should be tested by direct and trustworthy means.


  1. 1

    Phil. Mag., 42, p. 440; 1921.

  2. 2

    Phys. Rev., 36, 1668; 1930.

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ASTON, F. Atomic Weight of Cæsium: Use of the Word ‘Mass-spectrograph’. Nature 127, 813 (1931).

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