few rains. These seasonal effects have occurred each summer and wintercycle. Autoradiography” of part of a sample of percolated rainwater taken in winter from the chamber containing the large pieces of MHFT-12 revealed 0.05- to 0.8-um-diam plutonium oxide par- ticles with a count median diameter (CMD) of0.095 um. These accounted for only 1 ppm of the total plutonium in the sample, indicating that nearlyall the plutonium particles carried through the soil by water were less than 0.05 um in diameter. Usually there is good agreement in measured radioactivities among aliquots from the same per- colated rainwater sample. Occasionally there is disagreement with one aliquot counting as much as several hundred timesthe others. This indicates the presenceofa significantly larger than average particle of PuO.. We estimated that the largest particle foundin the high activity aliquots was equivalent to a 4-um-diam sphere, five times the diameter of the largest particle seen in the autoradiographic during the first 5 min of rain, in contrast to the ex- periment with the large pieces. Instead, airborne plutonium decreased, and after the rain, the concen- tration was an order of magnitude lower than before. These lower concentrations probably indicate that soll wetting inhibited resuspension of plutoniumbearing particles. The counting rates were so low that we had to combinethefive filters used during the rain to obtain meaningful statistics. The same treatment was necessary forthe first five filters used after the rain. There wasvery little seasonal effect on the plutonium content of the rainwater that percolated through the soil; it averaged about 0.2 uCi both winter and summer. 0 i st ~ ed |__| Ps 0 :S ot _-.-] 0 }| isk This concentration did not increase significantly oo TABLE V CONCENTRATIONS OF AIRBORNE PLUTONIUM DURING RAIN IN AN ENVIRONMENTAL CHAMBER CONTAINING FINELY DIVIDED 238-PLUTONIUM DIOXIDE Filter No. Collection Time __(nin) Pu Concentration (pCi/m*) 1 103 1.9 2 5 2.1 60 1.9 2-7 Remarks Before Tain First 5 min of rain Average during 13 164 0.12 926 0.14 After rain 3 63 | | jo 493] 33 1B 8 | | | 63 of4 tose} 7 7 I t _—— +~— 0 ——} p——J { 32 | ry i; | bo! .4 1 | 9, t [13 | 1 ' \ | EY 254 = ] 0 95 } oY of} LJ Tl PL62 ES o 6 | TG 0 23 ON = § k ‘ar {$3 foal 4 1334 4! | 0 BL PJ Tain 8-12 || of} E 2 |J = in the chamber were also measured using an air sampler. The results (Table V) show thatthe airborne plutonium concentration before the rain was about the same as the prerain concentration in the chambercontaining the larger pieces of MHFT-12. 0 — 0 analyses of a rainwater sample in which the count rates of the aliquots agreed. The fine particles of MHFT-12 interacted differently with the simulated environment. These particles were too small to have temperatures above ambient, so spallation was negligible. Plutonium concentrations in airborne particulates during a rain ! 066 69n0* fotI ! po ! ! 7 0 | — fb po 67; Jo | on ; r— of 0 {4 9 a2 Ld Oo; ee y [oe 0 = —y — W bs "4 23 132 35 088 — als 027 06 | | on Q 019 | + et lowe | — 6 = 6 7 0089 7 f= 13 pos [034 0} Vi FoF oy r— desl E+ LO Lo | bo) My| 10 40! Total a.Sampte to LFE Environmental . 12 [ow Lo lots 71a bad eat a XN 449s | ago [ol El 54 Core: positions: as * 6 ! Pu 5 2 4:7 Fig. 2. 238Py in soil cores from chamber containing fine material from MHFT-12 (ng).