72 WORLDWIDE EFFECTS OF ATOMIC WEAPONS both simple and possible to calculate from the available data of Eisenbud what fraction of the Sc*” from MIKE will have fallen out after 30 years if the presentrate of fallout continues unchanged. This would still seem to be a pessimistic assumption, and it is likely to give a number considerably less than 100 per cent. For low-yield bombs, the 100 per cent assumption is probably not unduly pessimistic. 5. Concerning assumption (4), experiments such as that of Dr. Larson, but conducted with Sr" rather than Sr*", are clearly desirable. General opinion seems APPENDIX I by you, namely, to assay the Sr®° content in bones of various animals including humans, and particularly in sewage and feces, at the present time to pet more reliable data.” CALCULATIONS ON ASSUMPTIONS OF H. A. BETHE The basic assumptionis to be that Sr°° would not remain exchangeable evenif it is so originally, "6. Concerning (c), it seemed to me that we should disregard the old data indicating about 30 parts of Sr per 1000 parts of Ca in soil. But that we might reasonably use the new data which give about three atoms of Sr per 1000 of Ca. This would still indicate an advantage factor of 10 for the incorporation of Sr into of uniform body radiation of gamma-rays. I believe that the accepted principle is correct according to which neutrons are much more dangerous than gamma-rays per unit energy. If this is teue, then also beta-rays must be much less dangerous than (2)..=(8) Ca or the bone as compared to Ca, and thus would increase the allowable fission yteld by a factor of 10. "7. Concerning (d@), I believe that the international tolerance of one microcurie of Sris really inconsistent both with the accepted tolerance of Ra and with that 73 ( <) Ca body Ca aol _ (e) body — Ca soll. Of so \ (Sr )eorr = (Ca) sors (= ) body alpha-rays. I further believe that it is really correct to make a direct comparison of With 1 yc of Sr®° fixed in the bone, we have over the bone. With these assumptions, onc gets a tolerance dose of 10 microcurics Sr 5 x 10-3 (© Yoo ~~ gga= FTO, a0 39 assuming that 1 cm? of topsoil weighs 30 gm, giving a content of 30 mg ofcal- beta-rays with gamma-rays provided the beta-emitter is really uniformly distributed of Sr? when distributed uniformly over the bone. This follows both from the accepted Ra tolerance and from the accepted gamma-ray tolerance. Of course, this number is entirely consistent with an assumed one microcurie if the latter is concentrated near the more sensitive parts of the bone, as it would probably be for an adult who has been exposed to Sr only for a few months or years. However, in this case the average bone of this adult will contain a lower concentration of Sr” compared to total Ca than the food which the person has consumed recently. This factor of uncertainty is eliminated when we talk about the level of Stin the food and in those parts of the bone which have been recently laid down. It seems to me entirely reasonable and safe to accept the 10 microcurie tolerance in connection with the calculations of c.ABRIEL. . "8. Concerning (e), nothing but renewed investigation of the chemical com- position of soils can help. If there is less Ca, the allowable number of megatons will be reduced proportionally. Concerning (f), Larson’s experiments seem to 1: ‘ Terre wath ju 14 ee f do Ghllim, "9. If the ratio of Sr’? to Ca in animal bones, etc., is equalto that of the soil from which the food is derived, or less, as it seems to be, then the application of bone mealfertilizer will not change the ratio unfavorably. “10. I think it és very essential to go through with the investigation proposed cium, and assuming 2(¢) in the previous section. The required amount of Srin soil to bring that soil to tolerance capability is 1.5 1O™ gm Sr’/cm? = 4 mg Sr**/mi?. The area of the earth being 2 X 108 mi?, the total requirement for tolerance is then 800 kg of Sr®°, which represents a fission encrgy of 800 MT.? PROJECT SUNSHINE FORMULA The energy release in megatons from fission bombs that would be required to bring the population of the earth to any given level T of Sr deposited in the skeleton, if the individuals grew from birth to maturity in an environment con- CamMmated Untormy produced, can be expressed by the following. (No decay of Sr°° is assumed and the Sr®° is assumed to be 100 per cent available for incorporation in the biological sequence from soil to man.) Let MT = the number of megatonsoffission energy released,