1
‘
3
i
4
t
Day
5
qt
6
t
7
qT
1
colated throughthe soil after the first rain contained
about 24 ng of plutonium in the chamber with the
8
t
+1600
nO 109
Ye
iGo 2
a
o
@ S00
3139'S
g
Ist Rein
2
3
a
& 4och
3
e
3
co §
300-
Ee
locK
to
l
i
2
i
a
4
l
Dey
I
T
the first rain (Fig. 5) seem to have been caused by
formation of a crust that partially insulated the
sphere from the water in the soil around it. We took
two sets of two soil cores from this chamber; none of
their sections showed appreciable alpha activity
above background except for the top two sections of
one core which contained about 0.2 ng each. The percolated rainwater and the dehumidifier condensates
also showed very little activity.
After a year of exposure to humid environment,
the PISA was removed from the environmental
chamber. We found a hard soil crust, 0.5 to 3.0 cm
thick, almost completely surrounding the PISA.This
crust insulated the PISA from the surrounding soil
and caused the change in temperature recovery
times noted in the series of rains in this chamber.
When the PISA was returned to the Plutonium
Metallurgy Group (CMB-5) for examination, it was
found that the iridium shell was intact and the vents
were plugged. There was no evidence that water had
penetrated the shell, or that any of the plutonium
had leaked out. The very small amount of 7*8Pu
found in the environmental system no doubt came
from contamination that was on the outside surface
of the PISA when wereceived it.
post-mortem
examination,
the
plutonium oxide material in the PISA was sorted by
indicating
the
presence of
content decreased for the next three rains, so that
there was less than 1 ng in the fourth rain. In the
chamber containing the fine material, the
carried out in the chamber containing the large
pieces of MHFT-27.
The plutonium contents of the dehumidifier condensates were similar to the contents of the early
condensates from the two chambers containing
material from MHFT-12. The condensates from the
fine material decreased in plutonium content after
the first rain, while the condensate for the large
pieces that was collected for a period that included
the rain had much more plutonium than the other
condensates from this chamber. Twosoil cores were
taken in each of these chambers at positions about
25 cm to the left and the the right of the PPO
material before the change to summerclimate. The
analyses for these cores are shown in Tables VI and
VI.
3. MHFT-50. The fragments of PPO from thetest
sphere MHFT-50 were placed in two environmental
chambers equipped with specially designed soil compartments. One chamber contains 186 ¢g of pieces
greater than 2 mm in diameter, and the other con-
tains 68 g of fine material, with particle diameters
between 0.01 and 2 mm. Thesoil in each chamberis
a loam, and thesoil tray is divided into two sections
by a circular partition 45 cm in diameter in the
Table VI
PLUTONEUM IN SOLL CORES FROY CHANUER CONTAINING FING MATERIAL FROM LRiFT-27
Lefe Core
Section
Ke,
particle size. One fraction of the material. consisting
of all of the pieces greater than 6 mm in diameter
(221 g), was placed in an environmental chamber,
and the fraction of the material with diameters
between 0.01 and 6 mm (32 g) was placed in another
environmental chamber. These chambers were initially programmedfor winter arid conditions. They
are now operating in arid summer weather. Each
chamber has had four rains. The water that per8
content,
summer in either of these chambers. The liquid
nitrogen rain experiment, described below, was
about two days before graduallyincreasing to about
500°C. The different responses to a later rain and to
this
plutonium
some large particles of plutonium. The plutonium
fourth rains were approximately the same. There
were no rains during the first three months of
I
6
Fig. 5.
Thermal responses of MHFT-27 to rain.
After
material. The water aliquots from the chamber containing the large pieces showed a wide variation in
plutonium content dropped to 0.5 ng in the water
collected from the second rain, and the third and
32nd Raln
& 200-r
large pieces, and 2.5 ng in the chamberwiththe fine
Right Core
Pu
sm ng
Section
Depth
Ne.
Lem
Pu
ng
1
0-3
g.45
1
0-4
2
3-3
O.19
z
4-10
3
7-10 < 0.03
5
10-13
0.03
a-s
13-17)
< 0.03
‘4
$-10
Total Tu
Depth
1c-14a
0,03
34-28 «< 0.05
9.67
412.)
0.16
6
37-19
0.07
9
19-23)
« 0.03
10
23-95
0.04
it
25-27)
« 0.03
12
27-28
9.)3
422.2