66 WORLDWIDE EFFECTS OF ATOMIC WEAPONS SAMPLING AND RESEARCH PROGRAM apparatus may need replacing or some one ofthe anti-coincidence shield- ations, similar to those above, show that it would probably be relatively easy to measure Sr°° in marine sediments, but somewhat moredifficult to measure it in sea wateritself, ing counters may cease to function properly and require replacement, but, generally speaking, the apparatus is rugged and trustworthy and can be depended on for continuous operation over long periods of time. The total cost would be in the vicinity of $3000, depending very largely on whetherthe electronics is purchased or constructed in the laboratory, The electronic components, as well as the anti-coincidence counter tubes, are available from commercial companies. The shield would require special construction. Sensitivity of Strontium Assay Procedure One could expect to detect some six counts per minute on a background of six with reasonable time and reasonable accuracy of measurement. This would correspond to a specific activity of 6/W puc/gm of sample, where W is the total weight of the strontium in the sample in grams. Thus a sample large enough to contain 10‘ puc/gm is measurable. Correspond- ingly smaller samples would suffice for materials of higher specific activity. With this result in mind one can speculatea little about the probable difficulties to be encountered in the worldwide Sr°° assay being recommended in this report. For a nominal atomic bomb of 20-KT energy that releases 1 kg of fission products, assuming a 5 per cent fission yield, 1.3 10" atoms of strontium are produced. Uniform dissemination of this material over the 5 >< 10'™ cm* area of the earth would yield a superficial Sr°° density of 7.5 & 10 * ppc/cm’. It seems very unlikely that the fallout strontium would have been mixed with more than 1 gm of strontium per square centimeter of the earth's surface, thus giving a specific Sr°° activity of 7.5 X 10° ppc/gm, which, as seen above, is measurable. We can probably conclude, therefore, that the Alamogordo bomb can now be detected in distant places of the earth if worldwide contamination 1s a characteristic OF explosions on reta- tively short towers. The specific Sractivity in soil today, assuming worldwide distribution, undoubtedly is considerably greater than that for the Alamogordo detonation alone, in view of the fact that many bombs have been fired, Consider- oo REFERENCES 1. Lipsy, W. F., Radiocarbon Dating, University of Chicago Press, 1952. 2. SuginarAa, T. T., R. L. WOLFGANG, AND W. F. Lipsy, “Large Thin-wall Geiger Counter,” Rev, Sct. Insir., Vol. 24, 1953, pp. 511-512. 3. Kurp, J. LaurgNCcE, AND LANSIN E. Tryon, ‘Extension of the Carbon-14 Age Method,” Rev, Sei. Enstr., Vol. 23, 1952, pp. 296-297.