ay
tegion and is strocgly absorbed by the ambient air.
The growth of the ses
level fireball is priscipally by hydrodyaxaics which form wery cuicaly and
carry sway most of the energy yield of the weapon.
Very little enerzy es-
capes the fireball before formation of the shock fronr which absorbs the
vadiant energy of the inper fireball, thereby decreasing the effective brightness of the X-ray beated air.
After breakaway, the expanding shock becomes
transparent and a second aaximm in the thermal pulse occurs which contains
essentially all the energy radiated from the burst.
The fraction of the
yield contained in the thermal pulse is about one-third of the total yield
for a sea level explosion.
+
Because of lower air density,
X-rays is deposited
in a larger volume at higher altitude.
The air tesperature of the fireball is
then somewhat lower than at sea level, and more of the radiant energy is in
the spectral region for which cold air is transparent.
Bydrodynamic phenomena
do not form as quickly as at sea level, so that more energy is radiated before
the thermal minimm.
This enhancement of the radiation constitutes a loss of
energy which would otherwise be carried sway hydrodynasically.
The result is
that bydrodynamics become less important and thermal radiation is increased
with altitude.
Depending on yield, there is an altitude at which there is no
second maxizam in the thermal pulse.
ton weapons.
This occurs below 200,000 feet for mega-
At still greater altituces, the portion of the yield that is in
thermal radiation begins to decrease again.
This is caused by X-ray deposition
which is so diluted spatially that the fireball] air is not very bot and cannot
radiate effectively.
11.2.1
Crexge
Shot Orang
S$ not expected to be substantially
different from sea level shots in sany respects.
At this altitude, X-rays are
still absorbed in a rather small region around the bomb.
Hydrodynaazic phenrca-
ena develop somewhat later than at sea level but still constitute the saost isportant mchanisa for transporting energy away from the explosion.
As at sea
level, a minim in the thermal puise occurs, although later than at sea level,
and relatively more radiation escapes in the early stages of the explosica
before the miniam.
Only a slightly larger fraction of tke yield is radiated
in comparison to that at sea level.
333