lated by choosing quantities for other elements found in soil which would maximize or
minimize the value of L but would not exceed the expected range of abundance of any
element. The relative standing of NTS soil is also shown in the figure. For the equilibrium spectrum, the figure shows that dose rates for soils containing equal amounts
of those elements which lead to gamma emitters on (n, y) reaction could be, at most,
30 percent higher or 56 percent lower than those at NTS.
Since neutron spectra from weapons can be softer than the equilibrium spectrum, a
Rel Dose Rate
1.0.
NTS Soil)
0.8
os
% Hydrogen by Wt
Figure 1.1 Dose rate versus hydrogen content.
similar evaluation of extremes for a 100-percent thermal neutron source was made. It
was shown that dose rates for a straight thermal neutron source would be, at most, 20
percent higher or 35 percent lower than for NTS soil.
From the evaluation of these extreme situations, it was concluded that neutroninduced dose rates can be predicted with reasonable accuracy with only a knowledge of
those elements whichproduce gamma-emitting radioisotopes. Thatis, for a given
spectrum, one set of K’s may be used in Equation 1.6 for all soils.
1.5
SUMMARY OF PREDICTION METHOD
Only three terms will be needed in Equation 1.6, one each for sodium, manganese,
and aluminum. Assuming that capture cross sections for these three elements have
similar behavior with neutron energy, for the equilibrium spectrum Equation 1.6 may
be written:
I = pmyK [ia Naye + 24.7 (% Mnye~ * + 60.3 (% Alpes | (1.7)
Where:
p
= density of soil (gm/cm*)
My
= gold neutron measurement or estimate (ny ~ Ny for a given spectrum)
K
= 3.93 0.15 x 107% (evaluated from NTS results)
12