A low counter background is obtained by use of steel for the shell and quartz for the counter window, while marked improvement in the stability is obtained by coating the window with an electrically conducting layer of tin oxide. The distribution of radon and its daughters within the counter under various conditions was determined by comparison of observed and calculated counting efficiencies. A stable counting efficiency of 5.58±0.05 cpm/μμc radon and a background counting rate of 0.08 cpm is obtained. The usefulness of this counter is augmented by adsorbing the radon on charcoal. The radon is then easily transferred to the counter with a small volume of helium and a Sigmamotor pump. This system is suitable for the analysis of samples of radon as small as 10−14 c or concentrations in air smaller than 10−16 C radon/liter.

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Hourly values of radon concentrations were obtained simultaneously at four levels above ground up to 39.9 meters on the Argonne Meteorology Tower on three separate days. Twenty‐seven consecutive hourly measurements were made on the first two days, and 17 on the third. Radon samples were obtained by adsorption on activated charcoal and were measured by means of scintillation counters. This technique, developed at Argonne, allowed direct measurement of radon instead of the common procedure of calculating radon values from measurements of daughter products. The large amount of meteorological data routinely obtained at the Argonne Meteorology Laboratory makes it possible to carry out detailed case studies on the relationship between radon concentration and the meteorological variables. This work has provided information on the heterogeneity of the horizontal distribution of radon. An inverse fumigation phenomenon was also observed. Under very stable nighttime conditions with light winds the radon concentrations observed at the top of the tower remained very low—about the same as during the daytime. Shortly after sunrise, with an increase in vertical mixing, the concentrations rose sharply. At a height of about 5.72 meters the radon concentrations on the clear nights ware larger by a factor of 20 than concentrations on the clear days. During cloudy conditions nighttime values were about twice as large as daytime values.

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Calcium-41 has been suggested as a new tool for radiometric dating in the range of 10(5) to 10(6) years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10(-14) and 3 x 10(-15) were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.