TABLE 6-3. ISOTOPIC ABUNDANCE FOR MIKE EXPLOSION PLUTONIUM
Isotope
Isotopie Abundance
(Atom %)
Fractional Alpha
Half-Life (Yrs)
Activity (%)
238
low
239
70.3
24,100
42.5
240
25.5
6,540
57.3
24]
87.8
2.74
low
6.10x10° @)
6.6x1074
14.4 (8
242
1.34
3.87x 109
5.1x1072
244
0.083
8.27x10%
1.4x107°
It becomes clear from the foregoing discussion that one can expect some variability in the 241 py
isotopic abundance in various samples taken at Enewetak Atoll.
Thus, the amount of
Am alpha
activity that has grown into these samples, relative to the plutonium content of the samples, will
show a corresponding variability. During the nominal 20-30 year decay time for these samples, there
has been opportunity for appreciable chemical fractionation between plutonium and americium,
depending upon individual sample history. For coralline soil samples that were exposed mainly to
rainwater, the evidence seems to show that the migration rates downward through the soil for
plutonium and americium are slow and not very different from each other. (Lynch, 1973) In Table
6~4 are listed activity ratios, total TRU for various types of plutonium as a function of time. The
two examples of plutonium with known abundances, “weapons grade" and Mike explosion material,
are compared with the median values for the total TRUe/241 Ame ratio from each island of the atoll;
the lowest and highest values are listed in Table 6-4. A useful, although coincidental, correlation
develops that the extremes in the range of median values for Enewetak samples are approximately
equal to values for the known Pu examples.
TABLE 6-4. ACTIVITY RATIOS FOR TOTAL TRU ALPHA ACTIVITY TO 241 4m ALPHA ACTIVITY.
Activity Ratio
Atom Ratio
(Total TRUa/ 24lAma)
241 py / 239,240py
20yr
50yr
Tyr
100yr
1000 yr
"Weapons-grade"
Pu (Table 6-1)
0.0055
7.7
5.5
5.3
5.5
17.7
Mike Explosion
Pu (Table 6-3)
0.0286
2.8
2.2
2.2
2.2
5.8
Enewetak 1972-73
survey soil samples
lowest
highest
3.0
10.
2.4
7.3
2.3
6.9
2.4
7.3
6.3
26.0
(range of median
values for each
island).
158