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GUDIKSEN ET AL.
a
© STRATOSPHERIC SAMPLES
57 -—Nb/ ICs
GC TROPOSPHERIC SAMPLES
10°
L
|
N DJ
1962
|p | {| |
|
FMAM J
| |
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JAS ON
1963
J
F
MA
1964
M
J
J
Fig. 6—Ratios of *Zr—*Nb/'3’Cs activities in stratospheric and tropoSpheric air samples.
tion gradient of fission-product debris in the upper troposphere. In
general, there is also a direct correlation between stratospheric and
tropospheric activity levels at any given time. This correlation indicates that rapid diffusion of nuclear debris is probably occurring across
the tropopause.
Figure 6 shows the ®Zr—"Nb/!3"cs activity ratios vs. collection
time. The ratios decrease with a 75-day half-life, which is close to the
half-life of ®Zr (65 days). The activity ratios for stratospheric samples are the same as for tropospheric samples collected at the same
time, thus indicating that no fractionation processes are operating
across the tropopause.
The “Mn/'"Cs activity ratios are shown in Fig. 7. A maximum
occurs
during April and May 1963; thereafter the decrease in the
ratio is consistent with the 300-day half-life of *‘Mn. Manganese-54