oA 1740-7
Eo (Mev/photon).
The procedure ‘'s as follows:
eo
Be7 (Hx) '
inxs
tha = KuagnE,
av
r/hr
(17-16)
where nE,
tt
Qo
the source strength in units of Mev/cm3-sec
and x = distance (cm) from the exposure point to the incremental
element of volume, dV
(ux)' = u)x,4px, where x) is the path length in air, xp 1s the
path length in the slab, and each uy,
is the total linear
absorption coefficient for the corresponding medium.
B
«8B fe, (ux) '] is the dose build up factor, as defined for
Equation 17-13.
Further, do, a symbolic dose-rate meusure of source strength may be
written:
z
do = KugnE, r/hr-cm
(17-17)
Note the difference ir units for do from a volume source (Eq. 17-17), and
from a point rource (Eq.17-14). When the concept is used for a plane
source in 17.45, dg will have the units r/nr.
This results from a
difference in the significance of n, which has the units photons, phgsane
and photons respectively.
eme-sec
Bec
(See also footnote after
cm
-sec
©
Equation 17-27, Section 17. 6.4.)
Then the exposure dose rate at the exposure point shielded by a
6lab of infinite radius is defined by:
Ghee = tof
However,
Ss av
r/hr
ships are not infinite in extent.
(17-18)
The slab of shielding
represents a ship's structure above the exposure point, and, in general,
is composed of a number of slabs of different sizes and thicknesses
(corresponding to a ship's decks and piating and determined by the
location of the exposure point).
Therefore, the slab must be bounded,
and for the idealized conditions of the problem, the individual slabs
are considered contiguous and are treated as a single whose total
thickness equals the sum of the thicknesses of the individual slabs.
Although the shielding slabs are rectanrular, it was found more feasible
to calculate the shielding effectiveness in terms of circular slabs that
BEST AVAILABLE COPY
17-58
aoe ee
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