Grade 10 Science – Unit 3 Lesson 9
Atomic Bomb
Energy generated by the explosion The atomic bomb dropped on Hiroshima, called Little Boy, 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. The energy created by the atomic bomb was “consumed” in three ways: 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, One-sixth of the energy was consumed when the explosion generated radiation. Task Draw a Pie-Chart to illustrate the energy consumption.
Heat On the ground, beneath the explosion centre (hypocentre), the temperature rose to approximately 3,800 OC. On the stairway of the entrance to a bank, which was 0.4 km from the explosion centre, 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 two kilometre radius from the explosion centre melted, and gray stones which contained silicon particles became white. In that same area, the clothes which people wore were burnt by the heat.
Atomic Bomb…2 Bomb blast
An ultra high pressure was generated by the explosion. The wind velocity on the ground beneath the explosion center was 1,580 km/hr, which is five times stronger than the wind generated by strong hurricanes. The pressure was 3.5 kg per square centi-metre (8,600 lb/ft2). At a point 0.5 km from the explosion centre, the wind velocity was 1,000 km/hr. Most of concrete buildings inside this range were completely destroyed. Even two kilometres from the explosion centre where the wind velocity was 300 km/hr, 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 0.2 km radius from the explosion centre, most people died within a few hours (even in the case where they were not directly exposed to the heat or wind). Within a 0.8 km, 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. Task Create a graph to represent the strength of the Bomb Blast from the centre of the blast.
Task Research the Manhattan Project. What was it? How did it work? Describe it.
Grade 10 History – Unit 3 – Lesson 9
Nuclear Bomb
On 6 August 1945 at 08:15 (Japanese Standard Time), the nuclear bomb Little Boy was dropped on Hiroshima. The bomb was dropped by the USA B-52 bomber Enola Gay. The strong wind generated by the bomb destroyed most of the houses and buildings within a 1.5 miles radius. When the wind reached the mountains, it was reflected and again hit the city. The wind caused the most serious damage to the city. About 68% of the city’s buildings were destroyed. The blast killed directly an estimated 80,000 people. In the following months, more people died from injuries or radiation poisoning. More than 140,000 people died within one year. In the end, the total number of people who have died was over 200,000. On 9 August 1945, a second atomic bomb, Fat Man, was dropped on Nagasaki. This bomb was bigger, but due to geographic position of Nagasaki on open plains, the damage was less and fewer people were killed. At this site, 70,000 people died within one year. Twenty-three American POWs were killed in the Hiroshima blast. Was the Nuclear Bombing of Japan necessary? The war in Europe ended May 1945, but Japan still fought frantically. Its military was still very strong. USA demanded the unconditional surrender of Japan. The Japanese rejected the demand. They feared for their Emperor (…who was considered a God…) in an unconditional surrender. The USA could have offered to retain the Emperor as a peace condition. USA desired revenge for Pearl Harbour. Within the USA military, there was desire to test a new weapon and demonstrate military might to the world. In 1938, the League of Nations established an international law (Protection of Civilian Populations against Bombing from the Air in case of War). Bombing of civilians was illegal. Recall, the USA, Germany and Japan were not members of the League of Nations. USA President Roosevelt noted that (1) bombing of civilians was barbaric and (2) Allied
forces should not undertake civilian bombings…if the same rules of warfare are observed by the enemy. In July 1945, Japan sought Russia’s help to end the war, but Russia declared war on Japan. With Russia as its ally, the USA could have threatened to invade Japan on two fronts. The Japanese were never threatened with the atomic bomb (i.e., surrender or we will use it). The bomb was just dropped. An American sea blockade had effectively stopped the flow of war materials to Japan, and the USA bombings were destroying the Japanese war factories. USA leaders wanted to minimize the loss of American lives in a prolonged ground war. It was estimated another 500,000 American soldiers would be killed in a prolonged fight with Japan. The estimate has since been challenged and losses were set at 40,000 killed. The USA dropped its second bomb only three days after the first bombing. They did not wait very long to see if the first bombing would build momentum for peace. Within Japan, people seeking peace were often killed by the Japanese military. Still, the “doves” would have fought if their Emperor was threatened. Many American scientists working on the bomb petitioned the USA Government not to use the weapon unless the Japanese Government was fully advised of the bomb. The Director of the Project would not allow the petition to be forwarded. (NOTE: His position on using the bomb changed after WWII) On 14 August 1945, the Japanese Emperor ordered his people…and thus, the Government of Japan…to surrender. Was it necessary? What were the outcomes in the world? In 1955, 25 Japanese women disfigured by the blast and radiation went to the USA for reconstructive surgery. The 25 women, called the Hiroshima Maidens, underwent 138 surgeries. Their journey was sponsored by a Christian charity.