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T HE total neutron cross sections of polyethylene (for hydrogen), beryllium, carbon, titanium, 1 vanadium, 1 zirconium, 1 and lead were obtained from a good geometry transmission measurement using neutrons from the University of Pittsburgh cyclotron, made available through the courtesy of Dr. A. J. Allen. Neutrons in the energy range of 13 to 15 Mev were detected by allowing the neutron beam to impinge on a polyethylene radiator and then detecting recoil protons by passing them through a proportional counter telescope 2 made up of four counters in a triple coincidence, anticoincidence arrangement. Suitable aluminum absorbers were placed between the polyethylene foil and the front counter of the telescope and between the last two counters in order to determine the lower and upper energy limits, respectively, of the sensitive range of the counter telescope. The mean neutron energy was 13.9 Mev.The samples whose neutron transmissions were measured were placed midway between the cyclotron target and the polyethylene foil of the neutron detector. The largest sample subtended a plane angle of 5° at the detector. Hence, it was necessary to correct each observed cross section for the effect of neutrons scattered elastically into the detector from the sample. This correction was calculated using the method of McMillan and Sewell. 3 Table I lists the observed cross sections, the elastic scattering corrections, and the corrected cross sections. The errors due to counting fluctuations are considered to be much greater than any others inherent in the method used, since the measured transmissions were corrected by measurement of stray neutrons scattered into the detector from the surroundings. Hence, the standard deviations listed with the corrected cross sections were calculated only on the basis of counting statistics. 4 The last column of Table I lists nuclear radii calculated from the corrected cross sections by the relation: o-< = 27ri? 2 .

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