1 ‘ 3 i 4 t Day 5 qt 6 t 7 qT 1 colated throughthe soil after the first rain contained about 24 ng of plutonium in the chamber with the 8 t +1600 nO 109 Ye iGo 2 a o @ S00 3139'S g Ist Rein 2 3 a & 4och 3 e 3 co § 300- Ee locK to l i 2 i a 4 l Dey I T the first rain (Fig. 5) seem to have been caused by formation of a crust that partially insulated the sphere from the water in the soil around it. We took two sets of two soil cores from this chamber; none of their sections showed appreciable alpha activity above background except for the top two sections of one core which contained about 0.2 ng each. The percolated rainwater and the dehumidifier condensates also showed very little activity. After a year of exposure to humid environment, the PISA was removed from the environmental chamber. We found a hard soil crust, 0.5 to 3.0 cm thick, almost completely surrounding the PISA.This crust insulated the PISA from the surrounding soil and caused the change in temperature recovery times noted in the series of rains in this chamber. When the PISA was returned to the Plutonium Metallurgy Group (CMB-5) for examination, it was found that the iridium shell was intact and the vents were plugged. There was no evidence that water had penetrated the shell, or that any of the plutonium had leaked out. The very small amount of 7*8Pu found in the environmental system no doubt came from contamination that was on the outside surface of the PISA when wereceived it. post-mortem examination, the plutonium oxide material in the PISA was sorted by indicating the presence of content decreased for the next three rains, so that there was less than 1 ng in the fourth rain. In the chamber containing the fine material, the carried out in the chamber containing the large pieces of MHFT-27. The plutonium contents of the dehumidifier condensates were similar to the contents of the early condensates from the two chambers containing material from MHFT-12. The condensates from the fine material decreased in plutonium content after the first rain, while the condensate for the large pieces that was collected for a period that included the rain had much more plutonium than the other condensates from this chamber. Twosoil cores were taken in each of these chambers at positions about 25 cm to the left and the the right of the PPO material before the change to summerclimate. The analyses for these cores are shown in Tables VI and VI. 3. MHFT-50. The fragments of PPO from thetest sphere MHFT-50 were placed in two environmental chambers equipped with specially designed soil compartments. One chamber contains 186 ¢g of pieces greater than 2 mm in diameter, and the other con- tains 68 g of fine material, with particle diameters between 0.01 and 2 mm. Thesoil in each chamberis a loam, and thesoil tray is divided into two sections by a circular partition 45 cm in diameter in the Table VI PLUTONEUM IN SOLL CORES FROY CHANUER CONTAINING FING MATERIAL FROM LRiFT-27 Lefe Core Section Ke, particle size. One fraction of the material. consisting of all of the pieces greater than 6 mm in diameter (221 g), was placed in an environmental chamber, and the fraction of the material with diameters between 0.01 and 6 mm (32 g) was placed in another environmental chamber. These chambers were initially programmedfor winter arid conditions. They are now operating in arid summer weather. Each chamber has had four rains. The water that per8 content, summer in either of these chambers. The liquid nitrogen rain experiment, described below, was about two days before graduallyincreasing to about 500°C. The different responses to a later rain and to this plutonium some large particles of plutonium. The plutonium fourth rains were approximately the same. There were no rains during the first three months of I 6 Fig. 5. Thermal responses of MHFT-27 to rain. After material. The water aliquots from the chamber containing the large pieces showed a wide variation in plutonium content dropped to 0.5 ng in the water collected from the second rain, and the third and 32nd Raln & 200-r large pieces, and 2.5 ng in the chamberwiththe fine Right Core Pu sm ng Section Depth Ne. Lem Pu ng 1 0-3 g.45 1 0-4 2 3-3 O.19 z 4-10 3 7-10 < 0.03 5 10-13 0.03 a-s 13-17) < 0.03 ‘4 $-10 Total Tu Depth 1c-14a 0,03 34-28 «< 0.05 9.67 412.) 0.16 6 37-19 0.07 9 19-23) « 0.03 10 23-95 0.04 it 25-27) « 0.03 12 27-28 9.)3 422.2