Low flux multielement instrumental neutron activation analysis in archaeometry

Abstract

A rouline instrumental method has been developed for theanalysis of 35 elements in potsherds by means of neutronactivation analysis at fluxes of 2 h). This re-striction was necessary because of a physical separation of thelaboratory from the nuclear reactor employed in activationand/or because of the limiting of access to relatively highneutron fluxes in conventional reactors. +It is not impossible to use conventional reactors to deter-mine elements producing short-lived radioisotopes in ceramicmaterials (6), but the extra work required to produce satis-factory results appears to make the task impracticable on aroutine basis.Low flux reactors, such as the SLOWPOKE (Safe LowPower Critical Experiment) reactor at the University of To-ronto (7), allow access to relatively low neutron fluxes(1Qtt-1gtz nlcm2 s) and can be most profitably employed forthe analysis of short-lived isotope-producing elements inpottery.The flux limitations of such a reactor are obvious, but arenot sufficient to eliminate their use for the analysis of elementswhich produce long-lived isotopes. As an example, at theSLOWPOKE reactor, cobalt in potsherds (averages 5-30ppm) may be determined either by the production 6f 6{)mQo(10.5m half-life) or by the production of 6oCo (5.26 yearshalf-life).Since the number of elements previously studied has beenrestricted by analytical technique rather than geological orceramic considerations, a program was instituted to developa more comprehensive multielement analytical scheme whichcould be routinely applied to the analysis of potsherds.Because of the stable nature of the neutron flux in theSLOWPOKE reactor system (8), multielement standards arenot normally employed in the routine analysis o1'samples.The present work described an INAA procedure in which35 elements are quantized for each potsherd. Included areelements indicative of the provenance and the method ofproduction of the ceramics.EXPERIMENTALSamples and Standards. Two Standard Ref'erence Materials. Cloal(SRM 1632) and Fly Ash (SRM 1633), from the U.S. National Bureauof Standards, Washington, D.C., were analyzed as were samples o1'