Measurement of and Calibration for Gamma Spectroscopy of Mississippi River Water.

摘要

Natural sources and industrial operations are known to introduce radioactive materials into the Mississippi River. The current investigation was undertaken to extend qualitative and quantitative knowledge of specific radionuclides in river water through the application of gamma-photon scintillation spectrometry. Raw river-water samples,collected from the intake pipe at a Jefferson Parish water treatment plant,were counted as one-liter aliquots in a Marinelli beaker for 12hours with a 4-inch by 4-inch NaI(Tl) crystal housed in a large graded-steel shield. Net peak areas from multichannel analyzer data for gamma energies of interest were obtained by subtraction of 12-hour background counts. A novel technique for establishing counting yield as a function of energy was developed to obtain both energy baseline and quantitative information from sample gamma spectra. This technique involved activation of selected target nuclides by Californium-252neutrons,with the product radionuclides first being quantitated by point-source counting,and then dissolved for counting as one-liter samples in the Marinelli beaker to provide empirical counting-yield data. Only naturally-occurring radionuclides were detected,with Potassium-40being the major contributor;up to 90 picocuries per liter of this radionuclide were observed. Suggested improvements in methodology include use of large-volume semiconductor detectors and longer counting times to obtain greater specificity and sensitivity.