Abstract
The mass spectra of four rare earth elements have been photographed, by the use of a spark source for the ions. New faint isotopes have been found in all four. The mass numbers of the new isotopes and rough estimates of their abundance in percent are: Gd, 154 (1.5), 152 (0.2); Dy, 160 (1.5), 158 (0.1); Er, 164 (2), 162 (0.25); Yb, 170 (2), 168 (0.06).

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