-4> =e ate yy of two isotopes of plutonium is seriously inconsistent with the negligible influence of isotope effects on the chemical kinetics of heavy elements. Thus it seems necessary to exp.ain this apparent solubility difference on physical grounds. 238puo, 2 The specific activity of the 79° Pud, particles (~80% and ~20% 29°Pu0,) was about 220 times that of 73°Pu0., . 2 In addition the ? 3 Pud, particles exhibited a very significantly lower density than the 78° Pud, particles (30) » indicating a highly faulted structure and weakened intermolecular bonding for the ?3°Pu0, particles. Fleischer (21) proposes that the apparently higher dissolution rate for 738 Pud, may be explained by the alpha recuil nucleus ablation of the surface layers of the particles, with a fragmentation rate proportional to the specific alpha disintegration . . . rate and with variable sizes of fragments ranging up to ~10 4 - atoms. The poorer structural integrity of the 23° Pud, particles may give rise to an ancrease in tne size range of ti.e ejected fragments. Such smail fragments, renging pp to tens of angstroms in diameter or more, would pass readily through the 0.1 pm diameter pores of the membrane filters used in the dissolution experiments (29) . Also, such small ablation fragments may exhibit a much higher mobility in tissue than that of 0.1 to 1.0 yn diameter, the size range of particles used in wost animal inhalation experiments. This greater mobility for very small ablation fragments in tissue may explain the observed more rapid rate of translscation for 235 Pud, than for 73*puo 9 from the lung to the liver and pone (32935). Ancther explanation for the apparently higher solubility of 233pu0 than 73®Pu02 is the possibility that the intense alpha radiolysis of the _ lung fluid at the surface of the particles leads to the production of chemically active free radicals which in turn react with Pud , molecules on the particle surface. This process aiso would proceed at a rate proportional to specific activity and to particle surface area. : ot, In this TyFUN : sy pea Way F, oF ae RFK 2