collected 25 cm to the left and to the right of the sphere. In each core there was onesection with a very small amount of plutonium (0.1 and 0.03 ng). The plutonium in the other sections was not distinguishable from background. A Chromel-Alumel thermocouple was attached to the side of the GIS with an epoxy adhesive. During the winter cycle the external temperature varied between 180 and 192°C. After the change to the summercycle, the temperature increased to 200 to 210°C. During a rain the temperature dropped below 50°C, and when the temperature and humidity controls were shut down, resulting in air stagnation, the temperature rose to 235°C. 5. Spallation Induced by Liquid Nitro- gen. Earlier work has demonstrated that the airborne plutonium concentration increased dramatically during a rain on large, thermally hot PPO pieces. This has always been presumed to be the result of thermal shock to the fuel’s surface, resulting in the spallation of tiny fragments of plutonia. We decided to find out if this cooling mechanism was a general phenomenon,or if water played a significantrole in the process by meansof a chemical reaction with the hot fuel. We conducted an experiment where liquid nitrogen drops fell.on chunks of PPO fuel in one of the environmental test chambers. This liquid nitrogen rain continued for 5 minutes. Air samples were taken before, during, and after the rain. We found that the airborne plutonium activity increased by four orders of magnitude at the onset ofthe cooling period. About an hourafter the end ofthe liquid nitrogen rain the airborne plutonium concentration had dropped back to its prerain level of 0.1 nCi/m?. These results are quantitatively similar to those found with aqueous rains, and suggest that hydrolysis reactions are not involved in the spallation process during an aqueous rain. The air filters on which the plutonium was collected contained a short-lived alpha activity, in addition to the the long-lived plutonium activity. the liquid nitrogen rain. Very little was found on the stainless steel surface. We also made background measurements on a separate set of the same kinds of surfaces by exposing them to the chamberair for 48 hours before the liquid nitrogen rain. The fact that significant amounts of alpha activity were found on the glass surface suggests that spontaneous spallation occurs continually, most likely caused by radiation damage in the plutonium oxide. A third set of adsorber measurements was made one dayafter the liquid nitrogen rain. These results showed far lower adsorption rates than existed prior to the liquid nitrogen rain. Apparently the thermal shockof the rain not only causes a great increase in spallation, but also frees loose particles created by radiation damage, so that at the end of the rain a fresh, undamaged surface is exposed. Significant soil contamination was observedafter the liquid nitrogen rain. The radioactivity, however, was found only on the soil surface and not beneath the surface. This is unlike soil contamination in the case of aqueous rains, where some of the plutonia particles are transported downward through thesoil by the rainwater that drains through the soil. Thus hydrodynamic transfer is a significant transport mechanism under aqueousrain conditions. III. DISSOLUTION RATES OF 7%pu0., IN PERCHLORIC ACID (James H. Patterson, Gilbert B. Nelson, and George M. Matlack) This experiment has been terminated. A topical report has been completed and will be issued as LASL report LA-6184. IV. SORPTION OF PLUTONIUM BY SOILS This short-lived activity was not present in samples (Gilbert B. Nelson, Nicholas Vanderborgh, George M. Matlack) plutonia, but also radioactive gases (72°Rn and 222Rn) entrapped in the plutonium oxidecrystal lattice structure. During this experiment we also measured the adsorption of the airborne plutonia on four different types of surfaces: glass, Teflon, stainless steel, and Lucite. Glass was the most effective collector of the airborne plutonia, adsorbing approximately 1000 times more than the Teflon or Lucite surfaces during Weare continuing the experiments to measure the absorption of plutonium by soils. This is done by collected prior to the rain. We believe that the thermal shock releases not only very fine particles of and allowing dilute plutonium to flow through soil contained in glass columns. Thefeed solution fed to the soil columns is a dilute, neutral solution of plutonium chloride, known to be unstable asit ages. This type of feed solution is necessary, however, to simulate rainwater contaminated with plutonium as it percolates through soils. 10 is VF