STRATOSPHERIC DISTRIBUTION OF NUCLEAR DEBRIS
307
shot, which produced that tracer nuclide. By mid-1963 the “Sr and
the ‘Cd concentrations had decreased substantially. Perhaps this
decrease resulted from dilution of the debris as it mixed horizontally
and vertically. At 90,000 ft at Mildura, relatively high concentrations of
Sr and ‘Cd were found by April 1963, and by mid-1963 they were
found «t still lower altitudes. Thus the debris from the Starfish Prime
injection, and perhaps debris from other high-altitude injections, was
moving downward through the stratosphere of the southern hemisphere
during 1963, causing changes in the concentrations of "Sr found at
various altitudes at Mildura. It is not possible to ascertain whether the
effective source region was in the tropical stratosphere near the
latitude of injection or whether this debris, like that from the Orange
rocket shot in 1958, entered the lower stratosphere in the polar regions
and subsequently spread equatorward.’?®
Additional information on the changes that occurred with time in
the stratospheric concentrations of *°Sr at altitudes below 70,000 ft may
be found in data obtained by means of WU-2 aircraft sampling in Project Star Dust.
Monthly mean values of “Sr concentrations found at
45,000, 55,000, and 65,000 ft in the northern polar stratosphere at 65°N
are shown in Fig. 4. At all three altitudes there was a general increase
in concentrations between early 1962 and late 1962 and a general decrease between early 1963 and mid-1964.
10
TTT TTT TTT try rrr rrr rt
0s; ACTIVITY, DIS/MIN PER 1000 SCF
65° N
@ 65,000 FT
© 55,000 FT
A 45,000 FT
10
q
Piper i
tpt ti tert sy i
Lettttrpga tp titiii ia tit
JJASONDJFMAMJJASONDJFMAMJJASOND JFMAMJJASOND
1961
1962
1963
1964
Fig. 4—Trends in *Sr activity.