Advances in alpha liquid scintillation spectrometry

With the introduction of the technique known as Photon/Electron- Rejecting Alpha Liquid Scintillation (PERALS) Spectrometry, pioneered by W. J. McDowell in the 1970's, liquid scintillation has become a useful alternative to conventional alpha spectrometry techniques. Despite many inherent advantages such as ease of sample preparation, greater than 99% counting efficiency, and low backgrounds, the technique has yet to gain widespread acceptance. This research consisted of two separate parts, both aimed toward increasing the usefulness and level of acceptance of PERALS spectrometry in the scientific community. Part I of this work consisted of the development and testing of a new method for the determination of uranium in drinking water by PERALS spectrometry. In this method uranium was selectively extracted from an aqueous solution of DTPA into an aqueous-immiscible scintillation cocktail containing the extractant HDEHP. The extraction of uranium was found to be essentially quantitative under a wide variety of conditions. Under optimum conditions less than 1% of thorium, polonium, plutonium, americium, and radium were extracted. Because this method offered significant advantages in simplicity and speed over currently approved methods, it was proposed as an ASTM standard test method for uranium in drinking water and is currently awaiting final approval by ASTM. Part II of this work involved the development and testing of a number of potentially more environmentally-safe extractive scintillator solutions which might replace current toluene/naphthalene-based solutions. Approximately 50 extractive scintillator solutions were prepared using various combinations of six different solvents and five commonly used fluors. Both pulse-shape distributions (time spectra) and pulse-height distributions (energy spectra) were recorded for each new scintillator solution and compared with those of a comparable toluene/naphthalene-based extractive scintillator. Based on the comparison of these spectra, the solutions were ranked according to their time and energy resolution capabilities. Observations regarding phase separation characteristics and long-term chemical stability were made for each solution. Also, alpha background measurements were conducted for a number of the test solutions. It was concluded that it is technically feasible to replace toluene/napthalene- based extractive scintillators with more environmentally-safe solutions with only minor losses in extractive scintillator performance.