4,
Expected Diameter/Time Curves for Pinon
It has been shown that the energy release from a nuclear explosion in
an ideal medium is proportional to D> /t?, where Dis the diameter of the
symmetric shock front, and tis the time since detonation, at which this
diameter obtains.
In his theoretical derivation Taylor uses a quantity A,
which is proportional to p?/2 /;; similarly we have found it useful to deter -
mine a parameter 6 = p/t2/5 which is, like Taylor's A, approximately constant for a given shot.
The deviations of ¢ from a constant are indicative
of extraneous effects {such as varying gammaand also of large masses in
the vicinity of the immediate explosion); the constancy of @ and the length of
the interval over which it is constant lends confidence in the result.
Further,
a statistical analysis of the scatter of the experimental points in the constant@ region can be used to establish confidence limits for the yield of the explosion.
Figure 2, a log-log plot of the expected diameter-vs-time data for
yields of 1, 3, and 10 megatons, shows continuously increasing diameters,
and slight deviations from straight lines.
These deviations are magnified in
the ¢ vs t plot of Figure 3; it is clear that ¢ becomes constant for the interval immediately preceding shock-breakaway, and this interval is used for
scaling purposes,
After breakaway the shock front is invisible (although it
continues to grow with constant » for a while longer), and the fireball itself
lags behind.
The fireball edges become indistinct and diffuse, and measure-
ments are valueless as far as yield determinations are concerned.
An am-
bient air density p, = 1.15 grams/liter has been assumed in drawing these
curves,
The trend of the data, in the early stages prior to constant-$ growth,
is typical of shots which are exploded with only small amounts of material
in the immediate vicinity of the detonation.
When large masses must be
consumed in the early phases, the growth pattern may be altered drastically;
nevertheless it will settle down to the same constant 9.
5.
Growth into Inhomogeneous Atmosphere
The high-yield nuclear explosion results in a fireball of large physical
size.
During the period in which yield measurements are to be made the
top of the fireball may reach an elevation af about 3, 600 ft, where the den-
sity of the air is about 90 percent of that at sea level.
- 8 -
Thus the fireball