CHAPTER THREE
A critical feature of the Enewetak Radiological Support Project was timeliness. Early in the planning stages it became clear that traditional techniques
and methods of radiological survey would simply not be applicable in this
remote location and under these operational circumstances. DNA expected
to have as many as a thousand people conducting and supporting the cleanup,
and the mostcritical elements of their task would require daily and detailed
technical guidance from the ERSP. Thus, we could not afford the time
which would normally be required to acquire, package, ship (to home
laboratories), analyze, interpret and report upon the many thousands of soil
samples necessary to characterize the atoll’s islands. The new approach to
soil characterization, evolved during 1976, was to make the measurements
on the islands, in-situ, supported by only limited soil sampling to assist with
interpretation. Data were thus made available almost in real time, and the
data flow and resulting technical guidance were consistently able to keep
pace with the operational progress. This chapter describes the in-situ system
and its use. As a new application of technology under remote and difficult
circumstances, its success is a credit to those responsible for its design,
construction and operation.
Project Manager’s Note
ON-SITE RADIOLOGICAL MEASUREMENTS
W. John Tipton and Ray J. Jaffe
EG&G - Las Vegas, Nevada
3.1
AERIAL SURVEYS
Two aerial radiation surveys were conducted at Enewetak Atoll prior to actual initiation of cleanup
activities. These surveys were performed by the U.S. Department of Energy's Remote Sensing
Laboratory, operated for the DOE (and earlier for the AEC and ERDA) by the Energy Measurements
Group of EG&G.
The first survey was conducted in the fall of 1972 as part of a comprehensive effort to assess the
radiological condition of the atoll prior to developing a cieanup plan. Two large arrays of sodium
iodide (Nal) scintillation detectors were used, each containing twenty 12.7-em diameter by 5.1-em
thick thallium activated sodium iodide (Nal (TY) seintillation detectors, mounted inside a CH-53
helicopter.
Spectral data were acquired continuously in a 300 channel pulse~height analyzer and
stored on magnetic tape in 3-second data blocks. Position information was obtained with an inertial
navigation system and recorded each second on magnetic tape. All islands within the atoll were
surveyed at an altitude of 30 meters, with 45-meter line spacing. The radiation data obtained from
the aerial survey were processed to provide total terrestrial gamma ray exposure rate values
extrapolated to microroentgen per hour (uR/h) at the | meter level, as well as the individual
exposure rate contributions due
conducted over Yvonne. These
island photographs, formed an
cleanup plan. Complete results
to 137Cs5 and 88Co. A special low energy survey for 241 am was also
results, presented in the form of radiation contours superimposed on
integral part of the data base used for developing the Enewetak
for the entire reconnaissance survey are given in NVO-140,.
Although the 1972 aerial survey helped to provide a comprehensive overview of the radiological
conditions at Enewetak, only limited data were obtained for 241Am, which was to become the
indicator isotope for the cleanup project.
July
For this reason, a second aerial survey was conducted in
1977. This survey concentrated on measuring the 60 kiloelectron volt (keV) gamma ray from
Am and only covered the northern islands from Alice down through Yvonne. The 1977 survey
employed the same sodium iodide detector array as utilized in the 1972 survey. However, the
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