NRL REPORT 6374 ratio is quite different for the two conditions, as 1 ! 4 1 \ 4 ° shownin Fig. 2. The time parameter is removed from consideration in Fig. 3 by comparing directly the radon/RaB activity ratio with the RaC/RaB i { \ \ ba atom ratio (p), wherein smooth curves are obtained \ 2 \ E which intercept the p axis at 0.735 for the equilib- \ it \ > rium condition corresponding to infinite t:me. \ c2= 30}- 3 ,1 Interconversion of the single emission and continuous emission conditions can be obtained from the plot in Fig. 4, where the relative radon concen- uo < S \ © 4 z 3 CONTINUOUS EMISSION \ < ity on a filter are shown as a function of the mea- \ 4 * 20 trations in the air required to give the same f activ- OF RADON \ sured p value obtaimable from the same filter. \ SINGLE EMISSION \ OF RADON “a EXPERIMENTAL PROCEDURE \ ’ Air Sampling L 0.1 —_L 0.2 J 0.3 0.4 05 06 RoC /RoB ATOM RATIO (Pp) O77 08 Fig. 3 — Relationship between the radon/RaB activity ratio and the RaC/RaB atom ratio (p) for the conditions of instantaneous and continuous emission of radon from the soil. These curves are obtained by combining the data of Figs. 1 and 2. Airborne particulate matter and associated radioactivity have been effectively collected on glass fiber filters having an exposed area of about 25 cm? through use of positive displacement blowers (Roots-Connersville Models AF-24 or AF315) driven by 1-hp electric motors. Glass fiber filters have essentially 100% retentivity for the radon decay products at the air velocity employed (2) and, moreover, are essentially surface collec- tors; furthermore, no retention of the gaseous a nN radon by filters has been detected. In this study Gelman Type A filters were employed with the fairly smooth, screen-imprinted back surface used ‘as the collecting surface to reduce theeffect ofselfabsorption of radiation by the filter. The quantity of dust collected during the 20minute periods did not measurably affect the air flow (between 0.42 and 0.52 m/min, depending on the unit), though on occasion a definite imprint of i Oo nm RADON (CONTINUOUS) /RADON (INSTANTANEOUS) the dust was apparent. The air sampling equip- ment was calibrated against a rotameter-type flow meter as a function of pressure drop across the filter; flow was determined from pressure readings | a SEE aE 10 taken at the start and the end of the run. After the accurately timed 20-minute collection Lo OJ i 0.2 l 0.3 Roac/RoB | l | o4 as 0.6 ATOM RATIO (,p) period, the samples were transferred to other 07 08 Fig. 4 — Relative radon concentrations in the air under conditions of single and continuous radoninflux required to produce identical quantities of radon daughter products. The values plotted are obtained by direct comparison of the curves in Fig. 3. holders and counting was started 60 secondsfol- lowing termination ofthe collection. Radioactivity Measurements All radioactivity determinations were made under conditions of standard geometry and