41
removed
TABLE 17.
—
Sample number}
fore the: and direction
ras used, *_
1ed, and .
1s
samples j
-y ashed |
re,
SN HCI.
oh
roheey
cae
4.0
4.0
15.0
25.5
35.5
45.5
53.5
55.5
55.5
61.0
72.0
80.5
91.5
(101)
101
101
0.059 + 0.007
0.090 + 0.039
0.052
0.058
0.032
0.037
0.030
0.026
0.022
0.037
0.025
0.022
0.030
0.027
0.025
0.024
0.029
0.020
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
0.006
0.006
0.004
0.004
0.004
0.004
0.008
0.005
0.004
0.008
0.004
0.003
0.003
0.004
0.003
0.008
Ratio
210P9/20Ph
1.53 + 0.69
0.027
0.030
0.030
0.0067
0.089
0.041
0.036
+
+
+
+
+
+
+
0.034
0.037
0.023
0.023
0.025
0.023
0.020
0.51
0.52
0.95
0.20
1.382
1.55
1.638
+
+
+
+
+
+
+
0.66
0.64
0.74
0.69
0.85
0.90
0.94
0.006
0.020
0.018
0.017
0.002
0.013
0.006
0.043
+
+
+
+
+
+
+
+
0.022
0.020
0.022
0.020
0.020
0.021
0.021
0.021
0.25
0.94
0.60
0.63
0.11
0.52
0.21
2.10
+
+
+
+
+
+
+
+
0.87
0.92
0.75
0.76
0.79
0.88
0.73
1.11
Mean
0.0154 + 0.0023
0.85 + 0.61 (8.D.)
QO SOUTH
hickory and 50% and upwards in the oaks. These large
O NORTHEAST
errors in the oak data were caused by the low activities
in these trees and by the long (1 year) interval be-
tween acquisition of the specimens and analysis.
rT.
4& SOUTHEAST
A
ey
QO
wood are shown on semilogarithmic plots in Figures 34
; to 37, The 2!°Pb concentrations in hickory (Figure 34)
; are constant in the 20 outer rings or even increase,
0028
presumably because the **°Pb circulates. After this
0041 time the concentration drops off with a 21-year half0023 Ft lite, as shown by the close correspondence of the data
0025
points with the line representing the half-life of the
“Pb, That the concentrations are fairly constant
within a ring can be seen from the agreement among
4
CENTER
Q
°
\ = 2l.4yrs
2
The results of the 71°Pb analyses versus age of the
re
0.0116 + 0.0025
The fractional errors of the 7!°Pb data range from
about 5 to 20% and of the *2°Po from 10 to 20% in the
Although Students’ t-test shows the mean ratio of
esenta111+ 0.34 (S.D.) in the 74°Po to 7!°Pb concentrations
which
in hickoryto be significantly greater than 1.00 (P <
ily the
0.025), it is still very close to unity. For the white oaks
these means of 1.18 + 0.70 and 0.85 + 0.61 for I and
Il, respectively, beeause of greater experimental variations, are not significantly different than unity, indicatf ine that the 22°Po follows the *4°Pb in thetree.
0.02
Oo
20
040
60
80
!
1990
|
«120
AGE (YRS)
Fic. 34.—Variation of *°Pb specific activity with age of wood
in hickory.
as do those of the hickory. The fit of the data for
White Oak I is poorer, and for White Oak II poorer
the cireles representing values within a ring (or set of
rings) along one radius of the tree, and the squares and
yet, as shown by the upper sets of data points in Figures 36 and 37. The tendencyto level off with age indicates either that 10 to 30% of the 74°Pb cireulates in
hark, despite exposure to dust and weather, shows no
higher concentration of 2?°Pb than does the adjacent
210Ph is continuously being produced by parent nu-
triangles representing values along other radii. The
Wood,
The curves for the three oak trees are less spectacu-
—-4
26Ra,
pCi/g dry
0
og
centra-
4.0
210Po,
pCi/g dry
oO
n units
in each
‘Ings in
Te also
;
deter-
1-7
1-7
13-17
22-29
33-28
43-48
52-55
53-58
53-58
59-63
70-74
79-82
90-93
100
99-103
99-103
*0Pb,
pCi/g dry
oO
|
i
'
i
:
1-7
Meanage,
years
oO
2 calcu-
roactive
ated by
hod.)
e about
°Po the
level of
Ageof ring,
years
9
a
1 onto a
r which
2re then
growin, !
“dl. The ;
1W
N
os
33
4s
5s
Hs
WwW
N
7s
Ss
Os
[G38
11S center
Ww
N
2°Pb, 2°Po anp #@Ra CONCENTRATIONS IN WHITE Oak II
i
210Bb (pCi/gm DRY)
sarefully
iit and less uniform. The black oak data shown in
l'izure 35 do not fit the 21-year half-life nearly as well
these trees, that the early uptake of this nuclide was
greater than the morerecent, or that a “background”of
clides, **®Ra or 7°?Rn, present in the wood. Thus, if
values of 0.010 and 0.015 pCi/g are substracted from
each of the data points for White Oak I and White Oak
II, respectively, the points fall more nearly with a