islands where °°Co and ***Sb are now the primary contributors,
the 1964 soil data usually indicate that these two isotopes
contributed even a larger percentage of the total exposure
in 1964; often even larger than would be estimated from half
life alone, suggesting that weathering may play an important
role on these islands.
.
a
The concentrations of various radioisotopes in the soil
varied considerably from island to island with the islands
further from detonation sites exhibiting mostly fission
product activity, while islands close-in to detonation sites
exhibited a variety of both fission and activation products.
The particular y-ray emitters found on each island and their
relative concentrations are discussed further in Section IIT
which treats in detail the environmental radiation fields on
each individual island.
C.
Error Estimates and Data Evaluation
Error in Total
Gamma-Ray Exposure Rates ~
Based on our past
experience with these instruments, the consistency of the
field data, and the laboratory calibrations, total exposure
rates at Specific sites surveyed with the ionization chamber
and/or the spectrometer system are estimated to be accurate
to within 1 pr/hr.
Total exposure rates obtained with the
we
portable scintillation detector are probably about + 10% S.D.
and those with the G-M survey meters about + 20% S.D.
The
on
overall accuracy in the range of the measurements for the
sites surveyed is probably better than 10%.
Error in Partial Exposure Rates for Major Emitters - The
partial exposure rates obtained from the field spectrometric
measurements
for
*8"Gs,
="Co,
and **°sb are estimated to be
accurate to + 10% S.D. for the first two emitters and + 20%
S.D. for the latter.
The ~*°Sb estimate sometimes includes
a small contribution from *°*™Rh.
‘This estimate is based
on the calibration accuracy as well as the amount by which
the sum of the individual exposure rates differs from the
independently measured total exposure rate.
In most cases
this difference was less than 10% and is probably due to
errors
in the assumed depth distribution relaxation length,
non-uniformity of the radiation field,
ground
7