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785As to previous range measurements, it appears that our triton range, 60.0±0.6 mm, is in agreement with that found by Livingston and Hoffman, 10 viz. 59.0d=0.6 mm, and also with that found by Rumbaugh, Roberts, and Hafstad, 11 viz., 61 mm (which is, however, not claimed to be very accurate). The latter authors have determined the alpha-range, too, but their The threshold energy for fast neutron fission of thorium and uranium has been measured by using the neutrons from thin lithium films through the Li 7 (p,n) reaction. Neutron energy fission thresholds were found to be l.OiO.l Mev for U 238 and 1.10±0.05 Mev for Th 232 .The relative probabilities of K creation and beta-emission are calculated for both molecular and atomic tritium. This ratio is shown to be 0.0035 for the molecule and 0.0065 for the atom, assuming the maximum kinetic energy of the beta-rays to be 16.9 kev.

The results of a measurement of the slowing down distribution in water of neutrons from a point fission source to indium resonance energy, 1.458 ev, are given. The second, fourth, sixth, and eighth moments of the measured distribution are calculated and have the values, r̄2=184.7 cm2, r̄4=1.222×105 cm4, r̄6=2.27×108 cm6, and r̄8=8.6×1011 cm8.

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The mean square slowing down length, r̄2, has been measured for two aluminum light water mixtures, the aluminum-to-water volume ratios being 1:1 and 1:2 by volume. The values of r̄2 obtained are 460.7 cm2 and 297.4 cm2, respectively.