Ip =
Where:
0.3549
- C Lh, 4) K/h
(1.1)
C = curies per cubic meter
Lfh, 6) = a polynomial, dependent on the altitude of the aircraft, h; and half angle, 6
which subtends the diameter at the surface contarnination.
The canima rays from the fissicn products are assumed to have an effective gamund energy of
0.5 Mev when 1 to 6 days old (Reference 5).
This reference states quantitatively that gamma
curies and Lzta curies are nearly equivalent in this period.
Estimates based on this assumption indicate that contamination with a beta activity of 4.43 x
10°(dis/min)/liter at the surface shuuld produce a 1 mr/hr gamma flux at 3 feet from the surface,
when the diameter of the contamination is large enough to appear infinite (@ = 90 deg).
Figure 1.1
Coordinate system of gamma radiation from a water volume.
Fallout of 0.404 megacurie per naut mi? deposited in the sea, uniformly mixed to a depth of
60 meters (Reference 3 and Section 3.4.2), would produce a 1 mr/hr gammafield at 3 feet above
the surface.
The gamma dose rate at any altitude f,, related to the 3-foot value is expressed by the ratio
of the polynomials L(h, 90 deg). The altitude absorption 1/f, is plotted in Figure 1.2.
1.3.2 Fallout Contamination of a Land Surface.
When fallout is deposited on land, the con-
taminated area appears as a large plane source. At any point in the radiation field, the gamma
intensity will include contribution from a circle whose radius is determined by the absorption of
the gamma photons in air.
The dose rate (I,) above such a plane is given by the following equa-
tion (Appendix A, Equation A.15).
Ip = 3.4427 Cy J(h, 8) x R/hr
Where: C
J(h, @)
curies per square meter
a polynomial similar in construction to that in Section 1.3.1.
With the same assumptions as for the water case (Eo = 0.5 Mev and the ratio of beta and
gamma curies equal to 1), 2.1 x 10"(dis/min)/ft? of beta activity will result in a 1 mr/hr gamma
field at 3 feet from the surface, when the source diameter is proportional to @=90 deg.
13
A