Rancitelli, L.A.; Cooper, J.A. & Perkins, R.W. MULTIELEMENT ANALYSIS OF BIOLOGICAL MATERIAL BY NEUTRON ACTIVATION AND DIRECT INSTRUMENTAL TECHNIQUES., report, January 1, 1968; (https://digital.library.unt.edu/ark:/67531/metadc1033111/m1/1/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .