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Alpha liquid scintillation counting: past, present, and future

Description: Beta liquid scintillation counting has been used for about 30 years, and its effectiveness for alpha particles has been known for almost that long; however, the technique has not been widely applied to alpha particle detection because of poor energy resolution, high background, and variable interference from beta and gamma radiation. Beginning with the work of Horrocks in the early 1960s, improvements in energy resolution and background rejection have been made. Further developments at Oak Ridge National Laboratory over the past 10 to 12 years have resulted in improved methods of sample preparation (using liquid-liquid extraction methods to isolate the sample and introduce it into the scintillator) and better instrumentation, including electronic rejection of beta and gamma pulses. Energy resolutions of 200- to 300-keV FWHM and background counts of 0.01 cpm are now routine. Alpha liquid scintillation spectrometry is now suitable for a wide range of applications, from the accurate quantitative determination of relatively large amounts of known nuclides in laboratory-generated samples to the detection and identification of very small, subpicocurie amounts of alpha emitters in environmental-type samples. Suitable nuclide separation procedures, sample preparation methods, and instrument configurations are outlined for a variety of analyses.
Date: January 1, 1979
Creator: McDowell, W.J.
Partner: UNT Libraries Government Documents Department

Analysis of low energy beta-emitters

Description: A survey was made of the instruments used for the determination of low energy beta radioactivity. Techniques commonly used are gas flow proportional counting, liquid scintillation counting, solid scintillation counting, and internal ionization chamber counting, solid state detector counting, and radiochemical separation followed by counting using one of the preceeding techniques. The first four techniques were examined and compared with each other. The sensitivities of the techniques were compared on the basis of the detection limits quoted for instruments described in the technical and reviewed literature. The detection limits were then related to the occupational and public individual maximum levels for air and water. Attention is focused primarily on the continuous monitoring of air for /sup 3/H and /sup 85/Kr, a medium energy ..beta..-emitter. It is clear that several continuous air monitoring instruments are readily available for measuring low energy ..beta.. concentrations, even in presence of certain other activity, at occupational levels. However, these instruments do not typically have sensitivities comparable to the public individual levels. Moreover, their capabilities for giving results in real time and for differentiating among the radionuclides actually present is limited.
Date: October 1, 1979
Creator: Murphy, D.L.
Partner: UNT Libraries Government Documents Department

New advanced in alpha spectrometry by liquid scintillation methods

Description: Although the ability to count alpha particles by liquid scintillation methods has been long recognized, limited use has been made of the method because of problems of high background and alpha energy identification. In recent years some new developments in methods of introducing the alpha-emitting nuclide to the scintillator, in detector construction, and in electronics for processing the energy analog and time analog signals from the detector have allowed significant alleviation of the problems of alpha spectrometry by liquid scintillation. Energy resolutions of 200 to 300 keV full peak width at half maximum and background counts of < 0.01 counts/min with rejection with rejection of > 99% of all beta plus gamma interference is now possible. Alpha liquid scintillation spectrometry is now suitable for a wide range of applications, from the accurate quantitative determination of relatively large amounts of known nuclides in laboratory-generated samples to the detection and identification of very small, subpicocurie amounts of alpha emitters in environmental-type samples. Suitable nuclide separation procedures, sample preparation methods, and instrument configurations are available for a variety of analyses.
Date: January 1, 1979
Creator: McDowell, W.J. & Case, G.N.
Partner: UNT Libraries Government Documents Department

Investigation of Cerenkov counting of environmental strontium-90

Description: A typical liquid scintillation counter was evaluated for detection of low levels of /sup 90/Sr-Y. A blank of about 5 cpm and /sup 90/Y efficiency of 42% were obtained for 20-ml samples. The corresponding minimum detectable concentration for a 100-minute count is 0.03 pCi/ml, so that measurement of water samples can readily be made at the maximum permissible concentration for /sup 90/Sr, 0.3 pCi/ml. The efficiency for /sup 90/Sr is less than 0.4%, 1.4% for /sup 137/Cs, and less than 0.04% for gamma-emitting /sup 85/Sr, a useful tracer. Some data for /sup 90/Y efficiencies and blanks are given for other liquid scintillation counters. Chemical treatments are necessary in some cases to concentrate /sup 90/Sr-Y, to remove colored substances which cause quenching, or to eliminate interfering radionuclides. However, the manipulations need not be as elaborate as in conventional radiochemical analysis methods for /sup 90/Sr. Ferric ion (yellow) quenches at the 5 ppM level, but the interference can be eliminated by adding a reducing agent. The Rn daughter /sup 214/Bi, an interfering radionuclide, disappears by decay in 2-3 hours after removal of Rn by sweeping with air or gas. Concentration-separation methods studied have included precipitation and ion exchange.
Date: January 1, 1979
Creator: Reynolds, S.A. & Eldridge, J.S.
Partner: UNT Libraries Government Documents Department