Introduction: About the A-Bomb



Introduction: About the A-Bomb

[pic]

Energy generated by the explosion

The atomic bomb dropped on Hiroshima generated a huge amount of energy when it exploded. The amount of energy generated by the bomb was equivalent to the amount of energy generated by a 15-kiloton TNT explosion.

Half of the energy was consumed when the explosion generated an ultra high air pressure which resulted in very strong bomb blast (wind). One third of the energy was consumed when the explosion generated heat, while the rest of the energy was consumed when the explosion generated radiation.

Heat

On the ground, beneath the explosion center(hypocenter), the temperature rose to approximately 7,000 degree F. On the stairway of the entrance to a bank, which was 1/8 mile from the explosion center, a man was sitting waiting for its opening. The surface of the stone stairway was changed by the immense heat. The part where the man was sitting remained unchanged because his body absorbed the heat.

Roof (ceramic) tiles on houses within 1/3 mile radius from the explosion center melted, and gray stones which contained silicon particles became white. The clothes which people wore were burnt by the heat within 1 1/4 mile radius from the explosion center.

Bomb blast

An ultra high pressure was generated by the explosion. The wind velocity on the ground beneath the explosion center was 980 miles/hr, which is five times stronger than the wind generated by strong hurricanes. The pressure was 3.5 kg per square centi-meter which is equivalent to 8,600 pound per square feet.

At a point that was 1/3 mile from the explosion center, the wind velocity was 620 miles/hr; the pressure was 4,600 pound per square feet. Most of concrete buildings inside this range were completely destroyed.

Even a mile from the explosion center, where the wind velocity was 190 miles/hr and the pressure was 1,180 pound per square feet, all brick buildings were completely destroyed.

Radiation

The explosion generated Alpha, Beta, Gamma and neutron rays. Alpha and Beta rays were absorbed by the air and did not reach to the ground. Gamma and neutron rays were strong enough to reach the ground; thus it was these rays that affected people.

Within 1/16 mile radius from the explosion center, most people died within a few hours (even in the case where they were not directly exposed to the heat or wind). Within a half mile radius, most people died within 30 days after the explosion.

The people who entered the area within a half mile radius from the explosion center in the first 100 hours after the explosion were also affected by the remaining radiation on the ground.

Fortunately it has not been observed that the long term effects of radiation affected A-bomb survivors nor that a radiation exposure caused genetic damages.

[pic]

The cumulative number of A-Bomb survivors who died during the period

By the end of 1945 the estimated number of people who died as a direct result of the bomb was 140,000. This graph shows the number of survivors who died up to the end of each year. The collection of statistics, by the Hiroshima City Government, did not commence until 1952. For the period 1946 to 1951 the number of deaths due to the bomb was estimated at 60,000. As the number of deaths among survivors, in the first ten years of the survey, showed little difference from the population as a whole it has been concluded that the number of people who died as a direct result of the bomb was approximately 200,000.

The Atomic Bombing of Nagasaki

At 11:02 a.m., August 9, 1945 an atomic bomb exploded 500 meters above this spot. The black stone monolith marks the hypocenter.

The fierce blast wind, heat rays reaching several thousand degrees, and deadly radiation generated by the explosion crushed, burned and killed everything in sight and reduced this entire area to a barren field of rubble.

About one-third of Nagasaki City was destroyed and 150,000 people killed or injured, and it was said at the time that this area would be devoid of vegetation for 75 years. Now, the hypocenter remains as an international peace park and a symbol of the aspiration for world harmony.(from Monumental inscription of hypocenter)

[pic]

DAMAGE CAUSED BY THE ATOMIC BOMB EXPLOSION

Levelled Area...................6.7 million square meters

Damaged Houses:

Completely Burned ------11,574

Completely Destroyed-----1,326

Badly Damaged------------5,509

Total-------------------18,409

Casualties

Killed------73,884

Injured-----74,909

Total------148,793

(Large numbers of people died in the following years from the effects of radioactive poisoning.)

Hiroshima during World War II

At the time of its bombing, Hiroshima was a city of considerable industrial and military significance. Even some military camps were located nearby, such as the headquarters of the Fifth Division and Field Marshal Shunroku Hata's 2nd General Army Headquarters, which commanded the defense of all of southern Japan. Hiroshima was a minor supply and logistics base for the Japanese military. The city was a communications center, a storage point, and an assembly area for troops. It was one of several Japanese cities left deliberately untouched by American bombing, allowing an ideal environment to measure the damage caused by the atomic bomb. Another account stresses that after General Spaatz reported that Hiroshima was the only targeted city without POW-camps, Washington decided to assign it highest priority.

The center of the city contained a number of reinforced concrete buildings and lighter structures. Outside the center, the area was congested by a dense collection of small wooden workshops set among Japanese houses. A few larger industrial plants lay near the outskirts of the city. The houses were of wooden construction with tile roofs, and many of the industrial buildings also were of wood frame construction. The city as a whole was highly susceptible to fire damage.

The population of Hiroshima had reached a peak of over 380,000 earlier in the war, but prior to the atomic bombing the population had steadily decreased because of a systematic evacuation ordered by the Japanese government. At the time of the attack the population was approximately 255,000. This figure is based on the registered population used by the Japanese in computing ration quantities, and the estimates of additional workers and troops who were brought into the city may be inaccurate.

The bombing

A postwar "Little Boy" casing mockup.

Hiroshima was the primary target of the first U.S. nuclear attack mission, on August 6, 1945. The B-29 Enola Gay, piloted and commanded by Colonel Paul Tibbets, was launched from Tinian airbase in the West Pacific, approximately 6 hours' flight time away from Japan. The drop date of the 6th was chosen because there had previously been a cloud formation over the target. At the time of launch, the weather was good, and the crew and equipment functioned properly. Navy Captain William Parsons armed the bomb during the flight, since it had been left unarmed to minimize the risks during takeoff. In every detail, the attack was carried out exactly as planned, and the gravity bomb, a gun-type fission weapon, with 60 kg (130 pounds) of uranium-235, performed precisely as expected.

About an hour before the bombing, the Japanese early warning radar net detected the approach of some American aircraft headed for the southern part of Japan. The alert had been given and radio broadcasting stopped in many cities, among them Hiroshima. The planes approached the coast at a very high altitude. At nearly 08:00, the radar operator in Hiroshima determined that the number of planes coming in was very small—probably not more than three—and the air raid alert was lifted. (To save gasoline, the Japanese had decided not to intercept small formations, which were assumed to be weather planes.) The three planes present were the Enola Gay (named after Colonel Tibbets' mother), The Great Artiste (a recording and surveying craft), and the Necessary Evil (the photographing plane). The normal radio broadcast warning was given to the people that it might be advisable to go to air-raid shelters if B-29s were actually sighted, but no raid was expected beyond some sort of reconnaissance. At 08:15, the Enola Gay dropped the nuclear bomb called "Little Boy" over the center of Hiroshima. It exploded about 600 meters (2,000 feet) above the city with a blast equivalent to 13 kilotons of TNT, killing an estimated 70–80,000 people. At least 11 U.S. POWs also died.[2] Infrastructure damage was estimated at 90% of Hiroshima's buildings being either damaged or completely destroyed.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download