Photon activation analysis (PAA) is a nondestructive technique for the elemental analysis of solid materials. Nuclei within a sample and a calibration material of known composition are activated via photonuclear reactions. Then, gamma spectrometry is performed on the sample and calibration material, and this allows measurement of the elemental content. Suitable calibration materials are limited in composition and their cost prohibits wide use of the technique. Development of calibration material in which the elemental composition could be customized for each analysis would allow wider use of PAA. A solid, homogeneous matrix is required for the calibration material. Polyacrylamide was selected for use as a solid matrix. A homogeneous, aqueous solution of target elements and acrylamide can be polymerized using an electron beam. This ensures both purity and homogeneity of the calibration material during polymerization. For development purposes, linear and crosslinked polyacrylamide were polymerized using two methods of chemical initiation: reduction-oxidation initiation and atom transfer radical polymerization. The focus of this research has been to characterize polymers by analyzing thermal stability, level of cross linking, size for linear polymers, conversion rate, crystallinity, and presence of the amide groups within the polyacrylamide. Chemically initiated polymers were analyzed using the following techniques. Thermogravimetric analysis (TGA) of both linear and crosslinked polyacrylamide showed clear differences between linear and crosslinked polymers. The tea bag swelling method showed crosslink densities varied depending on crosslink:monomer ratio. Kinematic viscometers were used to determine a range of sizes which varied with polymerization method and monomer:initiator ratio. Conversion rates were used to investigate the overall efficiency of the reaction over time and to determine the reaction times for desired sizes. Infrared spectroscopy showed that the amide groups remained intact even after the polymers were oven dried. X-ray diffractometry showed most samples were amorphous. This information will aid in determining methods necessary for characterization of the calibration material prepared via electron beam polymerization.

Characterization techniques for polyacrylamide used as a solid matrix in photon activation analysis

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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