TABLE 4—Filter-Paper Collections Made at Washington, D. C.* Bi fraction Pb fraction Date collected Volume processed Mar. 1-31 Mar. 21-31 Mar. 21-Apr. 24 Mar. 31-Apr. 24 Apr. 3-15 2X 10? 5 X 108 2.5 10'f 2 « 10° 1.5 X 10° (1960) (fe) B-achiuily a-activily B-activity a-activity 1,960 960 90 410 2 4 2 8 4,770 2,040 1,210 8,510 5,610 4 112 34 274 128 (dpm) (dpm) Islands, Kodiak) showless activity, and the collection made on a relatively small land mass far removed from continental areas (Samoa) shows the least activity. All of the bismuth fractions that were checked showed some a-activity (Po?!). Blower Collection Air taken from outside was passed through a 400 in? filter paper (Army Chemical Corps Type 5) at about 2,000 ft?/min and vented in such a manner that it was not drawn into the system again. At the end of the collection period the filter paper was removed and put into solution; the lead and bismuth were separated in the same manner as from thefloc. these materials in the atmosphere. It Filter-paper would be of interest to see how well such a determination would agree with the measured meanlifetime of about 15 days for RaD in the atmosphere as determined from comparisons of the short-lived radon decay products with RaD in the air (1). No attempt is made here to determine such a value since the Po determination was not made with sufficient accuracy. The results suggest several generalizations: 1. High-capacity air filters and rainwater collections effectively provide The remainder 2. The RaD activity collected by rain varies widely at different places (dpm) (dpm) ¥* Activity not corrected for decay, absorption or backscattering. + Filter used as backing for Mar. 21-31 and Mar. 31-Apr. 24 collections. of activity ; those on the coast (Panama) or on largerislands (Hawaii, Philippine Conclusions The presence of RaD and Poin the atmosphere suggests that a study of the ratio of these activities can lead to information relative to the lifetime of Chemical procedure. samples were dissolved by fuming with hot nitric-sulfuric acid mixtures to which a small quantity of hydrofluoric large samples of airborne natural radioactive decay products. of the procedure was the same as for and at different times at any given have been madesince the quantity of collected with the character of the rain, the seasons, or the quantity of dirt present in the collection from rain. acid had been added. the rainwater samples. Results. Results for the filter-paper collections (Table 4) were similar to those obtained with rain water. Only rough estimates of the volumes of air dust picked up by thefilter caused the flow-rate to decrease continuously. As considerable time elapsed between the dates of collection at the various sites and analysis at Washington, D. C., the RaD-RaE equilibrium had been reestablished and RaE measurements were essentially the measurements of the RaD parent in the sample. Printed in U.S.A, place. On the basis of present information, there séems to be no simple correlation of the quantity of activity 3. The average RaD activity varied by a factor of 10 between island sites, e.g., Samoa, and inland locations, e.g., Washington, D. C. BIBLIO GRAPHY I, I. H. Biifford, L. B. Lockhart, Jr.. H. B. Rosenstock. On the natural radioactivity ip the air, J. Geophys. Research ST, 499 (1952) 2. P. E, Damon, P. K. Kuroda, Nucireontica 11, 59 (1953)