MEASUREMENTS OF AIRBORNE RADIONUCLIDES AND DETERMINATION OF THEIR PHYSICAL CHARACTERISTICS R, W. PERKINS, C. W. THOMAS, and J. M. NIELSEN Hanford Laboratories, General Electric Company, Richland, Washington ABSTRACT Newly developed counting techniques that employ multidimensional gamma-ray spectrometry have been employed for the direct measurement of a large group of radionuclides in fallout samples. These techniques have made it possible to study the distribution of many of the trace constituents of fallout and also to improve the precision for the measurement of the more abundant radionuclides. The concentrations of ‘Be, ?Na, #Mn, C9, By 577—8Nb, 16Ru, 12 Sp 1255p HO B7Cg and '4Ce can be measured directly. Their concentrations in air during the past 2°), years are reported. The measured solubility of the fallout radionuclides is reported, and their deposition as dry fallout and as rainout in the area of Richland, Wash., is compared. The distribution and movement of the tracer radionuclides "y and !4Sb and of 7°°Pu both in the stratosphere and in the troposphere are discussed, The cosmic-ray-produced radionuclides Cl and *8S are mentioned, and their application along with other cosmic-ray-produced radionuclides in atmospheric research is considered. INTRODUCTION The absolute and relative concentrations of the various airborne radionuclides are of interest both in measuring their distribution and deposition rates and in studying the physical and chemical processes 198