Weapons tests to date (end of 1957) have produced about 6 and 11 Mc of SrYo and Cs137, respectively, of which about 1.9 and 3.4 Mc have been deposited as long-range fallout. Average surface deposition levels of SrSo and CsI3' in the north temperate population belt may be about 20 and 36 mc/mile2, respectively, and the stratospheric reservoir may contain an additional 2.3 Xlc of Sr90 and 4.2 Mc of Cs13'.Cesium-I37 contamination of the atmosphere and of drinking water, assuming they are in equilibrium with the rate of stratospheric fallout, does not appear to be a serious potential hazard to man's hcalth even though weapons tests continue indefinitely at the past rate.

No abstract

Precisely controlled localized irradiation of animal lung tissue can be accomplished using 10-pm diameter microspheres loaded with a radioactivity which are lodged permanently in the lung capillary bed following jugular vein injection. The spheres consist of biologically inert and insoluble ZrO, ceramic and are very uniform in diameter. The methods of preparation and analysis and the physical properties of the spheres are described.