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1673 246-, 318-, 475-, and 540-kev transitions. The counting rates were not high enough to determine if the gamma rays with energies above 700 kev are also in coincidence with this transition.The 0.48-0.54 Mev region of the pulse-height distribution is shown in Fig. 4. The normal pulse-height distribution is plotted in each part of the figure as a solid curve, and the distributions from gamma rays which are in coincidence with the 246-, 318-, and 475kev photopeaks are plotted as dashed curves in (a), (b), and (c), respectively. From these curves one can con-* These investigations were

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energy-level diagram for O 17 is included in Fig. 2, which also shows the 870.5±2.0 kev gamma ray reported by Thomas and Lauritsen. 10 The authors wish to express their appreciation for the assistance they received in the course of this work from the various members of the ONR Generator Group. We are indebted to Dr. M. M. Elkind, Mr. Walter J. Fader, and Mr. C. M. Braams for their help in obtaining preliminary data. We wish especially to thank those who read the photographic plates, particularly Mr. Absolute differential scattering cross sections for proton-proton scattering at laboratory energies of 5.77 and 5.86 Mev (±1 percent) have been obtained with an accuracy of about one percent at many angles (23° to 110° cm.) by two independent experiments, one employing nuclear emulsion plates as detectors and the other employing proportional counters. Reduced to the same energy, the average indicated S-wave nuclear phase shift is in excellent agreement with other data for this energy region. However, at small scattering angles, important for determining a P-wave phase shift, the measured cross sections differed originally by 3 to 5 percent, the nuclear emulsions method indicating a P-wave shift of -0.08±0.05 degree, and the original counter data indicating -0.34zb0.05 degree. After the beam collimation was improved and the energy spectrum of the incident proton beam was examined, check runs with the counters at six scattering angles failed to indicate the large P-wave effect, giving -0.08d=0.07 degree, in agreement with the emulsion data. It therefore appears likely that the P-wave shift at this energy is small (less than 0.1 degree) and negative, in agreement with other determinations in this energy region.