Chapter 2
PROCEDURE
Shot Cherokee, a:
air burst to be detonated 5,000 feet over Site Charlie, was
chosen to investigate tiduced activity from large-yield, thermonuclear weapons. The
ten types of soil used on Shot 5 of Operation Teapot (Reference 4) were exposed to the
neutron flux from Shot Cherokee near each of three neutron-detector stations of Proj-
ect 2.51, located at 80, 1,250, and 2,500 feet from the intended ground zero.
Also
exposed at each station were a sample of coral sand taken from the island and one sam-
ple each of sodium and manganesein the form of salt (NaCl) and manganese dioxide
(MnO,). The latter were included so that a long delay in sample recovery would not
result in a loss of all data.
All samples were exposed in watertight steel containers attached by °/, -inch aircraft
cable to large eyebolts set in concrete. The soil sample container was covered with
coral soil so that the neutron spectrum incident on the soil samples would be typical of
that 1 to 4 inches below the surface. This was thought to be the depth range for maximum thermal neutron density.
Recovery was made at H+6 hours by helicopter, and all samples were taken to Site
Elmer where the soil samples were measured with a gamma-ray spectrometer. Doserate measurements were made at each of the three stations by the recovery crew. . . When the results expected from Shot Cherokee were not obtained, Shot Yuma,a:
_
burst on a 200-foot tower at Site Sally, was chosen to investigate the effect of neutroninduced gamma-radiation fields on a soil different from Nevada soil. Samples of NaCl,
MnO,, and coral soil from the island were exposed at 100 yards ground range near Station 253.08 of Project 2.51. Six samples were exposed, each of the three materials in
a steel container about 3 inches above the ground and each in a thin aluminum container
about 1 inch below the soil surface. The activity of the recovered samples was measured in a gamma spectrometer, and the resulting spectra were determined as functions
of time for all samples. The dose rate near Station 253.08 was measured by a Rad-Safe
helicopter hovering at 25 feet at H+1.1 hours and by ground crews at H+3.4 and H+10.9
hours,
The gamma spectrometer used was the 20-channel differential pulse~height analyzer
manufactured by the Atomic Instrument Company, equipped with their Model 810 scintillator head, which contained a 2-inch diameter Nal well crystal. The primary calibration
was made with chemically pure NaCl and MnO,activated in the Los Alamos Laboratory’s
water-boiler reactor. Properties of the sample holder were minimized by substitution;
the same kind were used to obtain the final data and for the calibration runs. Calibrations
were made with the pure materials and witha mixtureof pure materials and coralsoil.
Calibrations involved about 2,000 counts per channel; final data runs, about 1,000. It
snould be noted that the spectrometer required too much maintenance to be entirely satisactory,
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