Moderation of 241Am-Be neutrons in paraffin wax

Neutron-flux measurements in a block of paraffin wax surrounding a 1 Ci 241Am-Be source have been made by activation of indium or gold foils. A discrimination between thermal and resonance neutrons was made by wrapping the foil in cadmium. Magnitudes of moderation parameters are derived and examined. The source of neutrons consists of 1 Ci of 241Am as the oxide compacted with beryllium metal and encapsulated in stainless steel (total emission 2.2x106 n s-1). It was obtained from the Radiochemical Centre, Amersham, and the capsule has the external dimensions 22.4 mm diameter x31.0 mm height. For the estimation of thermal neutron flux bare and Cd-covered gold foils were also irradiated. The isotopic activation cross-section for thermal neutrons for the reaction 115In(n,γ) 116Insub(m1) was taken as 155 barns and for the reaction 197Au(n,γ)198Au as 98.8 barns. Gamma rays of 0.417 MeV(30%) in the case of 116Insub(m1) and 0.412 MeV (95%) in the case of 198Au were measured. (F.Gy.)