Influence of the Moderator Size on the Slowing Down of (D, D) Neutrons in Paraffin Wax

Neutrons from a D(d, n)He³ neutron source, operating with 150 kev deuterons, were slowed down in blocks of paraffin wax. The distribution of 1.44 ev neutrons was measured with indium foils in five blocks of various dimensions, all facing the target with one of their end planes. The distribution was approximately the same in all blocks with thickness equal to or larger than 22 cm, which is about four times the slowing-down length in paraffin for (D, D) neutrons slowed down to 1.44 ev. Measurements were also made in a block of dimensions 50 x 50 x 100 cm³ with the target at the center. Even here the distribution of 1.44 ev neutrons was nearly the same as in the blocks already mentioned. The slowing-down age for (D, D) neutrons to 1.44 ev in paraffin wax, measured in the direction of the incoming deuteron beam, was found to be (33.0 ± 1.3) cm³.