The Velocity Dependence of the Absorption of Boron for Slow Neutrons

Measurements of the slow neutron velocity distribution between 1 and 10 km/sec. from a 14-cm cube of paraffin, with a source of 2.5-Mev neutrons in the center, show the distribution to be approximately Maxwellian with $T=400\mathrm{}$ °K, but with an excess of fast neutrons for $V>\mathrm{}3.5\mathrm{}$ km/sec. Similar measurements of the distribution of neutrons transmitted through a boron absorber verify the assumed $\frac{1}{v}$ absorption law in this velocity range.