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Hiroshima: Greatest Tragedy

Why Hiroshima Day?

At 8.15 am august 6, 1945, the first atomic bomb dropped in history exploded approximately 580 meters above the city of Hiroshima. In an instant, it reduced the city to a scorched plain, wiping out countless precious lives and inflicting devastation on all city structures. This unprecedented tragedy was on a completely different scale from the destruction caused by natural disasters or conventional weapons. Furthermore, the large amount of radiation that instantly descended upon the earth, penetrated deeply into people’s bodies, destroying cells.

The potential effects of radiation continue to threaten the lives of the survivors even today and have caused considerable psychological damage. Their extent is truly immeasurable. The physical damage caused by the atomic bomb ranges from injuries due to the severe heat rays and blast to cellular destruction from radiation. As the effect of the bomb continued to develop over a long period, the total number of dead depends on the date of the survey. It is estimated that in Hiroshima, the total number of people who died by the end of December 1945, when death from acute radiation disease had subsided, was approximately 140,000 (plus or minus 10,000).

Atomic Bombs:

1. Principles of Atomic Bombs

When the atomic nuclei in the center of an atom bomb, which is composed of fissile materials, are split, an enormous amount of energy is released in the form of high levels of heat and radiation. Atomic bombs use this energy as a weapon for killing. The splitting of atomic nuclei is called fission. When a single neutron strikes the nucleus of a fissile material such as uranium-235 (or plutonium-239); two or three more neutrons are ejected thereby releasing enormous amount of energy. The flying neutrons then hit other nuclei of the uranium and cause them to split in a similar manner, releasing more energy and neutrons. When this fission spreads, a huge amount of energy is generated instantaneously.

2. Development and manufacture of the first A-Bomb (The Manhattan Project)

Research on atomic bombs was started around the same time in several countries, including Germany, but in the United States , the actual building of an atomic bomb was already underway by 1942 under the code name ‘˜Manhattan Project’. The project was carried out in extreme secrecy using a large amount of the national Budget and outstanding scientists. In September 1944, it was determined that an A-Bomb would be used against Japan. On July 16, 1945 in the desert near Alamogordo, New Mexico, the United States successfully conducted the world’s first nuclear test. On July 25 immediately after the test, an order was issued to drop an atomic bomb on Japan. That order was written as follows.


War Department Office of the Chief of Staff Washington 25 DC


General Carl Spaatz

Commanding General

United States Army

Strategic Air Forces

July 25, 1945

a) The 509 Composite Group, 20th Air Force will deliver its first special bomb as soon as weather will permit visual bombing after about August 3, 1945 on one of the targets: Hiroshima, Kokura, Niigata, and Nagasaki. To carry military and civilian scientific personnel from the War Department to observe and record and the effects of the explosion of the bomb, additional aircraft will accompany the airplane carrying the bomb. The observing planes will stay several miles distant from the point of impact of the bomb.

b) Additional bombs will be delivered on the above targets as soon as made ready by the project staff. Further instructions will be issued concerning targets other than those listed above.

c) Dissemination of any and all information concerning the use of the weapon against Japan is reserved to the Secretary of War and the President of the United States. Communiques on the subject or releases of information will be issued by Commanders in the field without specific prior authority. Any news stories will be sent to the War Department for special clearance.

d) The foregoing directive is issued to you by direction and with the approval of the Secretary of War and of the Chief of Staff, USA. It is desired that you personally deliver one copy of this directive to General Mac Arthur and one copy to Admiral Nimitz for their information.

Thos T. Handy

General, G.S.C.

Acting Chief of Staff.


A field operation order dated August 2 stated that the day of attack would be August 6 and the primary target would be Hiroshima.

3. Outlines of the Hiroshima and Nagasaki A- bombs

Hiroshima Model:

To achieve chain-reaction fission, a certain amount of fissile material, called critical mass, is necessary. The fissile material used in the Hiroshima model was uranium 235. In the bomb, the uranium was divided into two parts, both of which were below critical mass. The bomb is designed so that one part would slam into the other by an explosive device to achieve critical mass instantaneously.

When critical mass is achieved, continuous fission (a chain reaction) takes place in an extremely short period of time, and far more energy is released than in the case of a gun-powder explosion. The Hiroshima model is known as a gun barrel-type atomic bomb.

Due to its long narrow shape, the Hiroshima model was called ‘Thin Man’ at first, but during the manufacturing process the original plans were modified by shortening the length and giving rise to the name ‘Little Boy‘.

The energy released from the Hiroshima A-Bomb was originally thought to be equivalent to the destructive power of 20,000 tons of TNT. Later estimates, however, put the energy equivalent to approximately 15,000 tons of TNT based on damage done to buildings and research on the bomb’s composition. Despite the release of such enormous energy, it is believed that less than one kilogram of the 10 to 30 kilograms of uranium 235 housed in the bomb achieved fission.

Nagasaki Model:

The fissile material used in the Nagasaki bomb was plutonium 239. The plutonium 239 was divided into below-critical mass units and packed into a spherical case. At the time of detonation, the units were compressed to the center with a gun-powder explosion to achieve fission. The Nagasaki model is known as an implosion-type atomic bomb.

Compared to the Hiroshima A-bomb, the one used in Nagasaki was larger in diameter and round, so it was called ‘˜Fat Man‘.

Only slightly more than one kilogram of the plutonium 239 is thought to have achieved fission, but the energy released is estimated to be equivalent, is estimated to be equivalent to the destructive power of about 22,000 tons of TNT.

4. Comparison of Damage in Hiroshima and Nagasaki.

*Height of explosion (Hiroshima) 580+/-20 m and Nagasaki 500+/-25m.

*Radius in which granite stone melted (Hiroshima) 1,000m (Nagasaki) 1,600 m.

By passing on the understanding of what happened that day, we hope to help others understand the spirit of Hiroshima or appeal for the abolition of nuclear weapons and the realization of lasting world peace.

*The article is written by Ph Nandakumar Sharma

(Courtesy: The Sangai Express)

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