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A dual measurement system for monitoring the simultaneous positions of multiple radioactive tracer pebbles in scaled pebble bed reactors (PBRs) has been developed and benchmarked to the prototype stage. The first system (the collimated system) is an updated version of a previously developed system that is now a completely automatic system that uses three collimated directionally variable Nil detectors that are programed to continuously search for a maximum counting rate from a single radioactive pebble. This system can be used by itself when a single radioactive tracer pebble is of interest and the pebble is relatively slow moving. In the present case, its primary use is to provide an independent measurement of the position of a stationary tracer pebble that is used to provide a point for calibration of the second system. The second system (the uncollimated system) is a modified version of a multiple uncollimated NaI detector system commonly called CARPT. The modified version involves those changes necessary to allow for use of the entire gamma-ray spectra for the inverse problem instead of only the gamma-ray full energy peaks. This allows one to use multiple radioisotopes each in a different tracer pebble so that up to ten individual tracer pebbles can be followed simultaneously with the best possible accuracy. The inverse problem is treated with the Monte Carlo library least-squares approach in which Monte Carlo-generated library spectra for each radioisotope are made available for a complete range of reference positions within the scaled PBR. Then, any unknown total gamma-ray spectra can be analyzed in an iterative fashion with the radioisotope library spectra to yield the position of all the radioisotope tracer pebbles. The scaled PBR used was a 30-cm-high and 30-cm-diam circular cylindrical section on the top and a cone with a 25-deg angle on the bottom. The pebbles are 1.2-cm glass marbles. Results have been obtained with both single tracer radioisotope marbles and multiple tracer radioisotope marbles, simultaneously. [ABSTRACT FROM AUTHOR]

Airport and airspace planners need a reliable method for quantifying the effects of nighttime operations on communities. Research has shown that cumulative metrics such as Lnight, Ldn and Lden show little or no correlation with aircraft noise event (ANE) produced awakenings. What is needed is a reliable method for quantifying the likely awakenings that will result from a full night of aircraft operations. This paper reports the results of an update of the analysis reported previously in Noise Control Engineering, 55(2). The objective of this present analysis is to refine the awakening dose-response relationships to be broadly applicable across airports and communities and it does that by adding European awakening data from Schiphol to the original data from three U.S. airports. It derives new regression coefficients and then tests two aspects of the results: whether the populations around the four airports are significantly different in their probability of awakening; whether coefficients that reflect subject "sensitivity" to awakening are real or a result of the random nature of awakenings. The first analysis used the awakening data collected by Sanford Fidell at Castle Air Force Base, Los Angeles International Airport and the new Denver International Airport. Since that analysis, the authors of the Dutch Sleep Disturbance Study (W. Passchier-Vermeer, H. Vos, J.H.M. Steenbekkers, F.D. van der Ploeg and K. Groothuis-Oudshoorn) graciously provided the data they collected in the vicinity of Schiphol Airport for inclusion in this updated analysis. [ABSTRACT FROM AUTHOR]