Detection of Fast Neutrons by Etch-Pit Method of Nuclear Track Registration in Plastics

Abstract

Plastics, such as polycarbonate, cellulose nitrate and cellulose acetate were irradiated with fast neutrons (2.5, 14MeV) and a count was made of the number of etch-pits on the surfaces of the irradiated material after etching with suitable chemical reagents. The experiments proved that the number of etch-pits increases with the etching time, and that at least during the early period of etching, a close correlation seems to exist between ΔP the increment in the number of etch-pits per unit area and Δl the increment of thickness of layer removed for a common increment of etching time Δt. In other words, an approximate relation ΔP/Δl=ρ was observed to hold during this early etching period, ρ being a constant that seems to correspond to the number of etchable damages produced by fast neutron irradiation per unit volume. The value of ρ was found to correspond roughly to the estimated number of recoil carbon and oxygen atoms in a unit volume in the case of polycarbonate which consists of carbon, oxygen and hydrogen. This indicated that the etch-pits observed in polycarbonate might have developed at the sites of radiation damage caused by the recoil carbons and oxygens due to fast neutron irradiation.