1°
433
Zz
31
~Y
wa
=
Z
a
Oo
W
_
ce
>
2 1
W
<
10°
0
|
0.2
!
0.4
|
0.6
ENERGY, MEV
|
0.8
|
1.0
1.2
ALTITUDE, 1000 FT
957,—Nib ACTIVITY, PC/45-MIN SAMPLING TIME
Fig. 4—Gross fission-product gamma-ray spectrum.
Fig. 5—Variation of %Zr—%Nb activity of stratospheric and tropo-
Spheric air samples. No samples were collected between August and
November 1963. Data were obtained with sampler shown in Fig. 1.
Since the sampling altitude was generally maintained near 30,000 ft
on the outward flight and near 40,000 ft on the return flight and since
the height of the tropopause varied from flight to flight, the data show
that the distance below the tropopause generally determines the ac-
tivity levels of the tropospheric samples. Thus there is a concentra-