assumedto be so in the calculation. The total dose rate d ata height 3 feet above a uniformly contaminated infinite plane is given by:
;
i=m
d= YD nidi
i=l
Where: dj = dose rate in Mev min~!cm™at height,
photonsof initial energy,
(4-1)
x above an infinite plane emitting
Ej isotropically at the rate of 1 photon min™'cm~?,
hy = number of photons min~!cm~?of initial energy, Ei:
The dose rate, dj is defined by:
oo
_ Ej h(Ei)
aE
e~§ ds Bi (ti)
ti
(4.2)
5
Where: E; = initial photon energy.
h(E;) = “true” linear absorption coefficient for air or fractional energy loss per
unit path length.
ty = Mix
x = 3 feet
Hy = total linear absorption coefficient for photons of energy Ej.
Bi(ty)
= i. buildup factor or ratio of dose from a]l photons to that from un1 - yj
scattered photons.
yi = fraction of dose from source energy E;, delivered by scattered photons;
y; is obtained from Curve A, Figure 20, Reference 1.
The value of the exponential integral may be found in prepared mathematical tables
(let s =tj).
Values of yy and h(E;) are compiled in Reference 1.
E; was taken as the mean
energy of the ith finite energy interval in the experimentally determined spectrum
(Reference 2). The actual calculations were carried out as described below.
Let R
gamma energy emission rate per unit area of the plane source in units
of Mev min~'!cm~?.
A = gammaactivity per unit area of the plane source in units of counts
min7‘!cm~?.
I
= gammaactivity per unit area of the plane source measured in a gamma
ionization detector whose response at various energies is known in
arbitrary units of mv em~?.
d, = dose rate at 3 feet from a reference source for which R = 1 Mev min™'em=*.
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