x i
0.2
1.2 a )
This equation offered a possible check on the empirical free-field determination by elect.
analog, provided that dIg/dt could be properly described by an arbitrary function genera
Otherwise a simplified version of the expression for S(t) could be solved by graphic iter:
as demonstrated in Reference 34. The analog solution requires the determination of the
ous constants of proportionality K,, K,, and Ky and a precise knowledge of decay at ear!
times. Although values for K, and K, can be easily determined and it might be possible
estimate K, by a Statistical analysis of the incremental collections, complete {nformatio
cerning early decay is required before an actual analog solution can be attempted. In fac
both methods of correcting for deposited activity are necessarily dependent upon an accu
knowledge of early decay. Unfortunately, the project was unable to include a detailed stu
early decay amongits objectives because of lack of both funds and personnel.
1.3.1 Components of the Radiation Field. Proper interpretation of the gross gamma }
depends upon the evaluation of the various sources of radiation outlined in the previous s«
Considering first only sources resulting from deposition during passage of airborne radix
material over the coracie, it is obvious that such sources do not exist until the station ha
engulfed by the radiating cloud. These deposited sources increase in relative importance
long as the station remains within the cloud, finally becoming the principal source of rad
after transit. Possible gamma radiation resulting from the upwelling of radioactive wate
rectly contaminated by the nuclear detonation is considered as a separate case later in th
section. The gross gamma record is therefore separated into radiation received from th
itself, from deposits on the coracle decks, and from deposited material suspended in the
rounding water.
The relative magnitudes of these contributing components are estimated using the gen:
expression (Reference 35)
dI =
L
|
da
B(E,,
e-Zux
4* ——_
{ 0s Dux)
ow
an(Zx)
where dI is incident radiation intensity from a source of intensity l and area dA ata di
x, B(E,, Zux)
is the buildup factor which is a function of radiant energy E, and the su:
the mean free paths Tux , and e- =X is the attenuation factor also dependent on the nu
of mean free paths involved. The gross gamma intensity Ig is expressed as the summat
the radiation intensities from the cloud l, from material deposited on the deck and the i:
ment case Ip and from fallout suspended in the surrounding water Iy .
The cloud intensity I, is determined by integrating over a hemisphere with the detect
its center and adding the contribution from a radiating slab whose thickness is equivalent
detector distance above the water surface (see Section A.1 for dimensions). Allowing the
and the hemisphere to extend to infinity, the integrated expression simplifies to
I, =
Sait)
—paz
Zz
(1+K) Zia {2-6 PA * A [- EL(- a2}
where K is a constant approximating the buildup factor in an expression of the form (1+K
Ja(t) is the source intensity for a unit volume of cloud, yu A iS the linear attenuation coef
for air, and z is the thickness of the slab. U*™ fission data (Reference 36) indicates tha
average gamma photon energy over the pericd of interest probably lies between 1.2 and 0
thus, a weighted average for linear attenuation coefficients and buildup factors can be de!
mined from standard references (References 37 and 38).
Using the values tabulated in S
A.1, the expression for the cloud intensity was evaluated at
31