-8- For a parabola described by the equation x = ky?, a line passing from a point (x), y,) on the parabola through a point (-x,, 0) on the x axis is tangent to the parabola at the point (x), Y¥,)) (Fig. 5). Inthe region of interest, the para- bolic arcs can be approximated reasonably well by straight lines. lector foil was cut (Fig. 6) into a series of pieces of equal area. The colThe method of cutting accepts particles of energies between 1 and 3 MeV per unit charge. These pieces were dissolved separately and analyzed radiochemically for a variety of fission products. The total remaining area of the foil in the quadrant where activity is expected was also analyzed to give a measure of the total beam intensity. A measure of background level was obtained by analysis of that part of the foil lying in the other quadrants. From Eq. (3) above, 7 =k: 2 + x; from the method of cutting, x is taken as constant. On analyzing for a product of a particular mass, we only expect to find activity for integral values of q. It is convenient, therefore, to plot a graph of counts per minute as ordinate against y" as abscissa, with y measured to the center of the trapezoidal section. We expect to find equally Spaced maxima, the difference in abscissa between maxima corresponding to a change of q of one electronic charge. The spacing between the ordinate axis and the first maximum should be the same as the spacing between adjacent peaks if the first maximum does indeed represent a singly-charged species. Figure 7 represents results obtained by counting the total gamma radia- tion emitted by sections of the collector foil cut as for analysis. The predicted positions of the various species are indicated on the figure, H and L standing respectively for heavy group" and "light group,'' and the number representing ionic charge. There is a general background level which is probably due to fission-product activity thermally evaporated from the source; however, 5001831