TABLE 3-2. THE CONVERSION FACTOR (s*/ p) / Np IN @Ci/g)/eps FOR 241Am AS A FUNCTION
OF DETECTOR HEIGHT, AIR DENSITY, SOIL DENSITY AND DEPTH DISTRIBUTION
Detector
Height, h
(em)
Depth
Distribution,@
(em7!)
Air
Density, Pa
Soil Density, Ps (¢/em? )
@/em®)
2.0
1.5
1.0
800
0.33
1.30
8.33
9.10
10.61
800
800
800
800
800
800
800
450
450
450
450
450
450
450
450
450
100
100
100
100
100
100
100
100
100
0.33
0.10
0.10
0.10
0.05
0.05
0.05
0.33
0.33
0.33
0.10
0.10
0.10
0.05
0.05
0.05
0.33
0.33
0.33
0.10
0.10
0.10
0.05
0.05
0.05
1.00
1.30
1.15
1.00
1.30
1.15
1.00
1.36
1.15
1.00
1.30
1.15
1.00
1.30
1.15
1.00
1.30
1.15
i.00
1.30
1.15
1.00
1.30
1.15
1.00
7,89
9.17
8.94
8.7]
9.35
9.11
8.88
7.45
7.39
7.29
8.22
8.11
8.00
8.38
8.26
8.16
6.67
6.67
6.66
7.36
7.35
7.35
7.50
7.90
7.49
8.63
9.49
9.24
9.01
9,52
9.28
9.04
8.14
8.03
7.92
8.50
8.39
8.27
8.53
8.42
8.31]
7.29
7.28
7.27
7.61
7.6)
7.60
7.63
7.63
7.63
10.06
9.60
9.39
9.1]
9.86
9.60
9.36
9.49
9.36
9.23
8.60
8.48
8.37
8.84
8.71
8.60
8.49
8.48
8.47
7.70
7.70
7.69
7.91
7.91
7.90
800
0.33
1.15
8.10
8.85
10.33
The mass attenuation coefficient for Enewetak soil was based on chemical analysis of 124 soil
samples obtained from 9 islands during December 1979. These samples were analyzed for organic
content as well as elemental composition. Results of the analysis showed that the primary
component of Enewetak soil is calcium carbonate. A number of trace elements were also identified.
The most significant trace element was magnesium, which contributed approximately 1-2 percent by
weight. Although the organic content varied from 0.5 percent to 25 percent by weight, most samples
were in the range of 1 percent to 8 percent, with an average of approximately 4 percent for all
samples. The in situ mass attenuation coefficient for each sample was obtained from a weighted
average of the water, organic and appropriate elemental mass attenuation coefficients. The water
content, by weight, for each sample was based on the in situ soil moisture measured with the nuclear
density/moisture gauge just prior to collecting the sample.
(All samples were dried prior to the
ehemical analysis.) The mass attenuation coefficient for organic material was estimated by using
the value derived for cellulose.
Based on these 124 soil samples, an average value of 0.333 + 0.012
em*/g was obtained for the in situ Enewetak soil mass attenuation coefficient. The average value
for the dry, organic-free component was 0.365 em2/g compared to 0.37 em2/p for pure caleium
carbonate. (Complete details and results for the soil density and mass attenuation coefficient
determination are given in Tech Note 22.)
Table 3-3 shows the effect on the 414m conversion factor due to variations (at the 1 and 2¢ level)
in the soil density and the soil mass attenuation coefficient. For a fixed mass attenuation
coefficient of 0.333 em4/g, a +2o variation in the soil density leads to approximately a +2 percent
change in the conversion factor. For a fixed soil density of 1.5 g/em’, a +20 variation in the mass
93