In order to untangle these overlapping distributions and arrive at the basic gamma lines, a method of graphical unfolding is used. present One starts at the highest-energy peak (assuming that it is not superimposed on the Compton distribution of a still higher energy) and measures the area under the total absorption peak. total ratio Then knowing the peak-to- (the method of ascertaining this ratio is des- cribed later) for each energy, one can calculate the area of the Compton distribution. After drawing in the Compton distribution of the highest energy, the process is repeated for the next highest-energy peak using the Compton of the highest energy as a base line. fe 7 The process is continued until all the energies present are analyzed. Knowing the resolution of the instrument for each energy, one can tell whether there is only one energy contributing to a particular peak, or two or more unresolved energies present, by the width of the peak. The resolution (width of a peak in kev at half-maximum height) was determined by measuring the resolution for several total absorption peaks of known energy and plotting the results (Fig. 4). In order to facilitate the measuring of the photopeak areas and to aid in estimating the relative size of two unresolved peaks,a series of Gaussian curves of predetermined widths, various heights and,thus, known areas, were drawn by means of a Gaussian curve generator (see Appendix II). 12 By