-9- tion of R and t to achieve cor proportional va mt dose for examination of the influence of variation in dose rate and time of "exposure may be useful for external sources of rediation which can be controlled with respect to R and t, but this manipulation is “artificial and unrealistic for internal alpha emitters which 4re not subject to such control of the variation in time of exposure. Page 6, "Hot" PuQ) Particle Risks - "If the above tentative conclusions are correct, then the same considerations must apply in the assessment of tumor risks for hot particles," Comments: The correctness of "the above tentative conclusions" are subject in part, at least, to previous (above) comments on the author's pages 4, 5 and 6. Page 6, lines 26-28 - "Raabe et a1. (29) report an apparent rate of dissolution of “°°Pu09 in lung fluid which is two orders of magnitude higher than that observed for 239P ud, particles," Comments: The 238pu0, dissolution experiments referred to were not carried out using "lung fluid", but rather a synthetic serum simulant. In addition, these experiments were conducted in vitro, not in vivo as is implied. Page 7, lines 5-8 - "In addition the 238pu05 particles exhibited a very significantly lower density than the 239Pu0, particles (39) | indicating a highly faulted structure and weakened intermolecular bonding for the 238pu0, particles." ‘ Comments: . Early measurements of density of Pud, with the Lovelace Aerosol Particle Separator system were highly variable due to experimental errors, with values averaging about 10 g/m; this value was reported for * Pwo, Improved techniques were developed by the time the *38Pu0, experiments were conducted and the particle densities measurements were more constant 3 and probably more accurate with average values around 8 g/cem~. That this difference in reported density was caused by "...a highly faulted structure