30 SUPERPOSITION OF aw” 60S. AND USSR _ BANDS 60 990 45 wv, O oO Sr) MC/SQ MILE 20 + NORTH o 30 LATITUDE 30 60 90 SOUTH Fig. 3— Theoretical latitudinal fallout profile, December 1957. } ¥ Poche short-lived radioactive daughters of characteristic half life and which can be repeatedly removed and measured since a new supply is grown into equilibrium each time a separation has been made. The importance of settling this point is obviously considerable for both meteorology and geophysics and certainly for the understanding of the mechanism of radioactive fallout. Perhaps the Ba!“ data will show the truth to lie somewhere between the two mechanisms. Bomb c!# ' Rafter” and Rafter and Fergusson™ have shown C* increases in surface air at Makara in New Zealand and in New Zealand woods and ocean carbonate as shown in Fig. 10. This additional C14 is due to bomb generated neutrons which react with air nitrogen to produce it. They find about 2.1 per cent increase per year. Williams* of Humble Oil and Refining Company, finds 3.0 + 9.5 per cent per year in Texas tree rings, Fig. 10, and de Vries® in Holland, and Munnich*in Heidelberg, Germany, both report increases. The C" increase in the flesh of the land snail, helix pomatia, amountedto 4.3 per cent between November 1953 and June 1957 in Holland, while an increase of about 10 per cent during 1955 and 1956 occurred in Heidelberg in various biosphere samples. At a rate of 2.5 neutrons per 200 Mev of energy release, one megaton would generate 3.2 x 108 c!4 atoms. The best estimate, keeping in mind that a substantial amountfalls back as calcium carbonate, would be that about 107° c!4 atoms have been introduced into the atmosphere, mostly into the stratosphere. The estimate of 2.5 neutrons per 200 Mev energy released is higher than an earlier estimate based on an assumed 15 per cent escape efficiency,“ the later value being based on firmer information. It also attempts to weigh fusion and fission as they have actually occurred. About 9.4 x 10?’ catoms are normally present in the stratosphere due to cosmic ray production.” This figure assumes 22 per cent of the atmosphere to be in the stratosphere. Therefore, with world-wide stratospheric circulation, the rise in the stratosphere should be about 100 per cent as was found ina few measurements made on samples collected in October 1956. Further measurements are in progress. 260 '