EVALUATION OF NUCLEAR EFFECTS IN THE ANALYSIS OF PLASTICS BY NEUTRON-ACTIVATION ANALYSIS

Validation of a method for the determination of trace elements in plas tic using neutron activation analysis (NAA) required evaluation of nuc lear effects. Since plastic is a moderator of neutrons, it is possible that the neutron flux may be affected in such a way as to effectively increase or decrease the measured activity of radionuclides within th e plastic. Such effects are likely to depend on the thickness of the s ample and so thicknesses of plastic ranging from 1 to 20 mm were used to quantify the effects. A standard containing vanadium (a thermal neu tron absorber) and silver (with epithermal neutron resonances) was use d in a sandwich of the plastic. The sandwich was then irradiated and t he standard counted. The activity of each radionuclide for each thickn ess was evaluated. The results showed that a variation of only 10% max imum was observed for thicknesses up to 20 mm. An increase in measured activity was observed for both the thermal and epithermal absorbers.