The altitude distribution of cosmic-ray neutrons has been measured from ground level up to 1175 ft using BF3 detectors on a television antenna tower. Neutrons of about 1-keV energy were measured by surrounding the BF 3 counters with cadmium-coated polyethylene cylinders. The flux near the earth was found to depend strongly on the soil water content. The distribution of neutrons below 1 eV was found from the difference in count rates of bare and cadmium-covered detectors and agrees with the result of a diffusion calculation. The neutron energy spectrum was investigated at the 45-and 1175-ft levels by counting with varying thicknesses of polyethylene surrounding the detectors, but little difference between the spectra for the two levels was discernible.

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We present measured angular distributions for n+-elastic scattering at 30 and 50 MeV from selected targets with A = 12 to 208. These angular distributions were analyzed using a phenomenological optical potential of first-order form. The mass dependence of the potential strength parameters displays the isospin dependence expected from the free mN interaction.NUCLEAR REACTIONS Elastic scattering of 30 and 50 MeV~from 2C, 0, 4 Ca, +Zr, Pb. Ai~ular distributions: 25'«z,~& 160 . Optical model ana1-ysis of cross-section data.

The simple principles of hydrodynamics which explain the unusual motion of a board skimming across shallow water are investigated to show the reason for the relatively slow loss of energy.