Walton, R.B.; Reilly, T.D.; Parker, J.L.; Menzel, J.H.; Marshall, E.D. & Fields, L.W. Measurements of UF$sub 6$ cylinders with portable instruments, report, January 1, 1972; (https://digital.library.unt.edu/ark:/67531/metadc1032400/m1/1/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .