Coincidence methods in low-level counting of neutron activated bioenvironmental samples

Although the counting techniques of instrumental neutron activation analysis (NAA) are well established in determining low level trace elements in bioenvironmental studies, little information has been reported in using more sophisticated coicidence methods to lower detection limits. Methods such epithermal NAA may reduce spectral backgrounds arising from activated products which exhibit 1/v cross sections. Radiochemical methods although very effective in determining many trace elements at the nanaogram and subnanogram level, are very time consuming, cannot be easily incorporated in large number of samples and sometimes are inappropriate when wanting to do multielemental analysis. Both Compton suppression and {gamma}-{gamma} coincidence methods are ideally suited in neutron activation studies, particularly in quantifying elements that are not usually determined. During the past several years our group has judiciously employed Compton suppression methods to determine several environmentally significant elements in airborne particulate matter, tobacco smoke, hazardous waste and botanical reference materials. Besides reducing the detection limits for copper, cadmium, silicon, nickel, etc. by suppressing the Compton continuum, spectra interferences are also significantly reduced particularly from radionuclides which emit coincident {gamma}-rays. This work will focus on the use of Comptons suppression methods and its value in environmental studies.