ATOMIC BOMB

1.Outline of Atomic Bomb

	(I) Hiroshima-type	(2) Nagasaki-type
Length:	3 meters	3.2 meters
Diameter:	0.7 meters	Diameter: 1.5 meters
Weight:	4 tons	4.5 tons
Element;	Uranium 235	Plutonium 239
Energy:	Equivalent to 20 kilotons of TNT in explosive power (However, it has been estimated that the yield was equivalent to approximatelv 1 3 kiloltons.)
	The explosion was caused by collision of two parts of critical amounts of uranium compacted in a iong.shaped bomb. The bomb contained 10~30 kg uranium; however the actual fission occurred in the first 1 kg, not leaving time for the rest of the uranium to generate a chain-reaction.	This was contained in a spherical casing, and the plutonium was pushed toward the center by the pressure of surrounding conventional gunpowder.

The blue bomb was called "little boy" and was dropped on Hiroshima
The yellow one was called "fat man" and was dropped on Nagasaki.

2.Comparison of the Atomic Bomb Damage between Hiroshima and Nagasaki

3. Fireball at the Instant of Explosion

The temperature at the instant of the explosion reached several million degrees Centigrade (maximum temperature of a conventional bomb is usually approximately five thousand degrees Centigrade). Almost simultaneously, a few millionths of a second later, the surrounding air reached white heat point and formed a huge fireball. 1/10,000 of a second later, the fireball had a diameter of about 28 meters and a uniform temperature of about 300,000 degrees. The fireball seen 9 kilometers from the burst point was of bluish-white or pinkish-white hue and had a luminosity of about 10 times that of the sun.
With the explosion, intense heat rays and radiation were radiated in all directions, and a blast occurred with the tremendous expansion of the surrounding air. It is estimated that approximately 35% of the total energy generated was thermal radiation, approximately 50% blast energy, and approximately 15% radiation energy (5% from initial radiation and 10% from residual radiation).

4. Velocity of Climb of Atomic Bomb Clouds

Soon after atomic explosion; an enormous pillar of smoke rose up and reached the bottom of stratosphere or the altitude at where the density of the air bubble is equal to that of surrounding air, and shaped a mushroom cloud, spreading out over several kilometers. This is the final stage of the process developing an atomic bomb cloud, which is ultimately dispersed by the wind.

Mushroom cloud seen from the arsenal at Kasumi-cho (2.7 kilometers southeast. Photographed by Tosbio Fukada.)