Chapter 4
DISCUSSION
4.1
and
CONCLUSIONS
DISCUSSION
By comparing Na” activities in the coral and NaCl samples (Table 3.2), the percent
by weight of Na in coral was determined to be 0.31 + 0.03. This is twice the amount
determined by chemical analysis (Table 3.1). The Na’ activity must be assumed to be
due to Na’ (n, y) Na’, since neither coral nor NaCl contains enough Al or Mg to produce
competitive amounts of Na*4 by (n,a) or (n, p).
For such small amounts of sodium, it is believed that the comparative activation
method is the more accurate. This could imply a consistent chemical error, because
two other samples of coral from Site Charlie (Namu Island, Bikini) show 0.16 percent
and 0.11 percent by chemical analysis. It is also possible that the sodium content in
coral may vary by as much as a factor of two within a small area.
From Equations 1.7, 1.8, and 1.9 and the neutron measurements of Project 2.51, dose rates were calculated at 1.1, 3.4, and 10.9 hours after zero time. Results are
shown in Table 4.1.
The greatest slant range at which a gold neutron measurement was made for Shot
Yuma was 604 yards. In order to make a dose rate calculation by the method of Reference 4, it mugt be assumed that the equilibrium spectrum was established at 604 yards
slant range.|
When the amount of sodium used for coral is that determined by the comparative
activation method, calculated values range from 1.33 to 1.25 times the values inferred
from field measurements. When the chemically determined value for sodium is used,
inferred dose rates are 1.50 to 1.6 times the calculated dose rates. This suggests that
the correct average sodium content for coral lies somewhere between 0.15 and 0.31
percent.
However, errors implicit in the prediction method and in field measurements
of dose rates do not allow confidence in this deduction.
Measured dose rates are probably subject to +25-percent error, and the estimated
probable error in prediction method is #30 percent. Assuming that these are the major
sources of error, agreement between calculated and measured dose rates is subject to
probable error of +40 percent.
20