The build-up of thermal neutrons with depth in soil is indicated by the relatively high
activity of buried samples; however, activity differences between buried and unburied
samples are greater than expected.
The samples which were exposed above the surface
may have been shielded somewhat by the sandbags which were used by Project 2.51 to
hold their detectors off the ground. AHMhough the samples were between the sandbags
and the device, shielding could still be significant because low-energy neutron flux is
nearly isotropic.
4.2
CONCLUSIONS
The difference between the effects of pure fission and fission~fusion neutron spectra
on induced activity in soil was not measured, since the soil samples on Shot Cherokee
were not activated.
However, a method for predicting neutron-induced gamma-radiation
intensities (Reference 4) was tested for coral soil on Shot Yuma. Predicted values were
within + 50 percent of induced dose rates inferred from field measurements.
22