EFFECTS OF DONTYTIWG RADELATION
8
the done at the center of the body is approsimately 3) perceet higher than ‘would rasuit
9) percent of the dose had been received. the
dose rate had fallen w lens than 40 percent of
from a given air dose with narres beaa. geometry. Figure 1.4 illustrates the depth dose
curve from an experimental mtuation using
St> initia! value. Tham tne cop rate ale differed frem the usual constant rate in the
f € F
i
o
qT
i
8
TOTAL OOBE IM AIM (1)
¢
1
laberatory.
o!
0
10
to
20
l
L
Ld
%
tt}
a
J
|
L
xO
TIME AFTER H-HMOUR (HR)
Frotec 1ib—T7he accumulation of gemma dose as ae function of time after
commcacement of fellout on Rongclap atoil.
In addition to the dose rate and energy dif-
spherically rented Co” sources with a phantom placed at their center, compared with a
conventional bilateral depth dose curve ob-
out radiation is signiticantly different from the
case, the air dose is usually measured at the
1.23
Geometry of the Exposure
ferences the peometry of the exposure to fall-
meng tea
usual Jaboratory sources. Since fallout radiation is delivered from a planar source the usual
narrow beam geometry is not applicable,
In
such a diffuse 360° tield, the decrease of dose
with depth in tissue is less pronounced than
that resulting from « bilateral exposure to an
X-ray beam because falloff from inv ye square
is in effect neutralized. For the sani energy,
tained with a single source (4).
In the latter
point subsequently occupied by the center of
the proximal surface of the patient or animal
with respect to the source. For the held case,
all surfaces are “proximal,” in the sense that
the nir dose measured anywhere in the space
subsequently occupied by the individual is the
same. Lt is this atr dose which ts measured
by a field instrument: it dues not bear the same