soon as fission is complete, and the study of fission yield as a function of mass can be carried out at a rate well suited to radiochemical or massspectrometric techniques. This is not true of nuclear charge; the vast ma- jority of fission fragments undergo several changes of nuclear charge via beta decay before heing transformed into species sufficiently long-lived for radiochemical or mass-spectrometric study, | ‘Some information is available; Wahl al.} have measured direct fission yields of two or three isobaric nuclides in each of several mass chains that are susceptible to rapid chemical separation. The technique is unfortunately, limited to regions with amenable chemistry and to species with half-lives of a few seconds or more. Cohen and Fulmer have made an ingenious applica- tion of the mass-spectrometric technique to the study of the charge distribution of fission fragments escaping from a thin source into low-pressure gas. From the observed relationship between mass resolution and gas pressure, they were able to deduce a ''width" of the charge distribution curve for the mass 97 fission product chain of about 2.2 charge units. It is unfortunatethat their method has an optimum mass resolution of several mass numbers. The study of the nuclear charge distribution of a large number of fission product mass chains demands a rapid separation of species. Such a separation need not isolate one single nuclide, although that would be the ideal case; it is enough to separate a small group of nuclides that can be measured in the presence of each other by suitable methods. Previous investigators have usually isolated a group of isotopes of a single element by chemical methods, An equally good method, permitting even simpler resolution, would be to isolate the isobars of a single mass number; for example, by passage through a mass spectrometer, In either case the amount of each species present in the mixture is determined by resolving the multicomponent decay curves, by 9001831