Theory of the Fireball

in the isothem. sphere. For its occurrence it is important that the
opacity actually decreases with increasing T at higher temperature. Many
calculations of K(T) in this temperature region have been made. Curves
have been compiled, especially by Gilmore,21 and revised as more mor-
mation has become available. The most recent and most extensive calcu-
lation, to my howledge, is by Stuart and matt. 22
AU. calculations agree that T 3 /K(T), which is the important quantity
according to ( 5.3), has a pronounced minimum at about T ’ = 2, T = 20,000°.
(The temperature of the minimum increases slightly with increasing den-
sity. ) Molecules are no longer present at these temperatures, and
absorption is mainly by bound-free electron transitions in atoms and
atomic ions, with some contribution from broadened atomic lines (bound-
bound transitions) whose calculation is the most difficult . Radiation
transport, then, is most difficult around Tb = 20,00O0, - and temperatures
around Tb constitute an effective blocking layer for radiation.
Until about 0.5 second, the central temperature of a 1-megaton sea
level explosion is greater than T according to the calculations of
b’
0
Brode. Radiation flm can then be considered as taking place separately
in an interior and an exterior region. The Stertor flaw is determined
by the central temperature Tc, and this flaw generally decreases with ,
time because Tc decreases and with it the quantity T 3 /K. The exterior
flaw is dominated by the cooling wave and increases with time because
the decrease of density causes a decrease of opacity for any given T.
The two flow regions are separated by a blocking layer in which the
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