630
FERBER
The detonations investigated were all air bursts over water during
Operation Dominic I at Christmas Island in 1962. Some data for surface detonations obtained by aircraft sampling during Operation Red-
wing in 1956 are used to compare withthe Project Stemwinder data.
The project was conceived as an attempt to utilize available sampling aircraft to narrow the area of uncertainty involved in two related problems. The first problem was concerned with the operational
need for prediction of the possible local hazards due to rainout of
radioactive debris from a portion of a nuclear cloud that might pass
over Christmas Island shortly after an air burst. Since the tops of
rain clouds in the Christmas Island area were generally below 20,000
ft, and often below 10,000 ft, the amount and distribution of activity in
the stem of the mushroom cloud was of primary concern. The second
problem was concerned with the partitioning of nuclear debris between
the stratosphere and the troposphere as a function of nuclear yield,
tropopause height, burst height, and, possibly, other factors. Such
partitioning has been an important consideration in estimating the
long-range fallout from nuclear tests since nuclear debris has a mean
residence time of several weeks in the troposphere (intermediate fallout) as opposed to many months or years in the stratosphere (worldwide
fallout), depending on the latitude and altitude of injection. The fraction of the debris which remains in the troposphere maybe particularly
important in considering the possible hazards from relatively short-
lived nuclides such as ‘841 since the stratospheric portion usually de-
cays to insignificant amounts before it can return to the surface of the
earth.
It is emphasized that the preceding remarks apply only to the very
small particles that contribute to the intermediate and the worldwide
fallout. In the case of surface detonations, much of the radioactivity is
associated with relatively large particles that comprise the local fallout. These large particles are not affected by the tropopause and
appear in the local fallout regardless of whether they are initially injected into the troposphere or into the stratosphere.
CLOUD HEIGHTS OF AIR BURSTS IN A TROPICAL ATMOSPHERE
Operation Dominic I shot data (including those for yield, burst
height, and cloud-top, base, and tropopause heights) are given in the
Project Stemwinder final report.! Since there was no scientific pro-
gram to document cloud heights, a “best guess” was made for each
cloud by evaluating estimates made by observers on the ground and in
the
sampling
aircraft and by using the dose
rates reported at the
various sampling altitudes to verify, where possible, the visual observations. Variations in the burst heights did not appear to have any