Photon Activation Analysis

A useful method in material investigation and analytical science

 

Dr. Christian Segebade
Federal Institute for Materials Research and Testing
Berlin, Germany 

Photon activation analysis (PAA) and other radioactivation procedures (activation analysis with neutrons or charged particles) are the only analytical methods based upon nuclear reactions.  Consequently, elements can be detected, and chemical species in several exceptional cases can be determined.  Most of the elements of the Periodic Table can be studied in multi-component material normally without any chemical treatment.  Samples are exposed to the activating radiation (in PAA, bremsstrahlung photons from a high energy electron source), whereby nuclear reactions are induced in the different elements.  Thus, radioactive atoms are produced whose characteristic radiations (preferably gamma quanta) are then measured with appropriate spectrometers.  PAA is not an “absolute” method, hence the samples under study have to be irradiated together with a comparative material sample (calibration material) with well-known chemical composition.  After spectroscopic measurement of both samples the quantitative evaluation is performed by comparison of the two resulting element spectra, basically following the same procedure as in most instrumental methods, e.g. ICP, AAS, etc.. The particular advantages of activation analysis are freedom from blank values, reduced danger of contamination and, since frequently investigations can be carried out “non-destructively”, easy handling of material difficult to treat chemically, such as refractory metals, dusts, ashes etc.  Another advantage is the option to study very small samples (a few milligrams) as well as very large ones (up to multi-kilogram amounts).  Basically, there are no limitations concerning the nature of material studied.  PAA has been applied to environmental studies, biochemistry, material science, geo- and cosmochemistry, certification of standard materials, forensic science, studies in art and archaeology and more (particularly for the latter application, non-destructivity is essential!).  Basic information as well as application cases will be presented during the colloquium.