mle effective in 2 bomb as U-235, is derived from the more plentiful U-238 isotope, but only through a chain reaction that depends on the presence of U-235, which is broken down in the process, It is doubtful whether a given quantity of uranium can yield substantially more plutonium than 235,36 It appears also from the Smyth Report that the amount of U-235 which can profitably be extracted by separation of the isotopes is far below 100 per cent of the amount present, at least under present technigues,.3/ What all these facts add up to is perhaps summarizedby’ the statement made by one scientist that there is a great deal more than enough fissionable naterial in lmown deposits to blow up all the cities in the world, though he added that there might not be enough to do so ifthe cities were divided and dispersed into ten times their present number (the Size of cities included in that comment was not specified), Whatever solace that statement may bring is tempered by the understanding that it refers to known deposits of uranium ores only and assumes no great increase in the efficiency of the bombs, factors likely to change? But how are these | It is hardly to be questioned that the present extraordinary military premium on uranium will stimulate intensive prospecting and result in the discovery of many new deposits. It seems clear that some of the prospecting which went on during the war was not without result. The demand for uranium hereto- 36. The Smyth Report is somewhat misleading on this score, in that it gives the impression that the use of plutonium rather than U-235 makes it possible to utilize 100 per cent of the U-238 for atomic fission energy. 2.26 and 4.25. ‘See paragraphs However, other portions of the same report give a more accurate picture, especially paragraphs 8.18 and 8.72-73. 3% Among numerous other hints is the statement that in September 192 the plants working on the atomic bomb were already receiving about one ton daily of uranium oxide of high purity (paragraph 6.11). Making the conservative as- sumption that this figure represented the minimum quantity of uranium oxide being processed daily during 19-45, the U-235 content would be about 115 pounds, The actual figure of production is still secret, put from all available indices the daily production of U-235 and Pu-239 is even now very considerably below that amount, "