Characteristics of positive ion emission for various compounds on a tungsten filament are noted. Methods of analysis of mixtures of radioactive isotopes by mass spectrograph are described. The following mass assignments are made: 108-day yttrium, 88; 57-day yttrium, 91; 1-year ruthenium, 106; 300-day cerium, 144; 3.7-year element 61, 147; 55-day strontium, 89; 25-year strontium, 90; 60-hour yttrium, 90; 12.6-day barium, 140; 40-hour lanthanum, 140.

• Received 3 June 1948

DOI:https://doi.org/10.1103/PhysRev.74.650