The threshold-detector system indicated free-field neutron doses
from 13,400 rep at 25 yards to 22.6 rep at 400 yards for Burst Hamilton
and from 273,000 rep at 10 yards to 428 rep at 300 yards from Humboldt.
The chemical-dosimetry technique resulted in no useful data.
--WT-1680
-
SOIL ACTIVATION BY NEUTRONS FROM A VERY-LOW-YIELD BURST.
Operation HARDTACK.
E. F. Wilsey, J. H. McNeilly, and R. J. Spitznas, July 1960.
SECRET-RESTRICTED DATA
es
(Supersedes in part ITR-1680).
Soil samples were exposed to Burst
amilton in order to (1) document the neutron-induced gamma field produced
by a fractional-kiloton nuclear device detonated on a wooden tower 50 ft
high, and (2) determine empirical factors relating the gamma dose rates
measured over this large neutron~-induced field with dose-rate measurements
made over small samples of the same activated soil.
The presence of
induced activity in the soil samples was determined by gamma spectrometer
analysis.
The maJor ggntributions to the gamma spectra in the soil
samples were A128, m8, and.yal at H + 16 minutes, Na@4 and Mn36 at
H+ 7 hours,
and Nae
and Fe79 at H + 54 hours.
The low-energy neutron
flux was found to peak at 5 to 8 cm below the ground surface of normal
Frenchman Flat soil and at the ground surface in more-moist Frenchman
Flat soil.
Empirical factors relating field dose rates with sample dose
rates cculd not be determined because of the low-level of induced activity
produced and the fission-product contamination of the project-station
exposure area.
The presence of fission products was indicated by the
typical Tission-product dose-rate decay demonstrated by the residual field
and by the presence of low-energy, fission-product-like peaks in the
gamma spectra of a ground-surface soil sample recovered from the vicinity
of ground zero at H + 31 hours.