Fireball from first nuclear bomb

Atomic bombs utilize the energy released by the fission of uranium and plutonium to generate far more destructive power than any conventional bomb not only in the scale of their explosions but also in their killing power. Not only do they create explosions, fireballs and shock waves, they also produce dangerous radiation which inflicts severe injuries on the human body.

The effects of a nuclear explosion include a massive explosive blast (shock wave), intense heat, electromagnetic pulse effects, intense radiation near detonation, death from trauma or significant radiation sickness from directed ionizing radiation and from fallout.

At Hiroshima, people within a kilometer of the hypocenter received life-threatening doses of gamma rays, neutron rays and other types of radiation. Fifty percent of the energy released by the bomb was in the form of shock waves; 35 percent was in heat rays, 10 percent in residual radiation and 5 percent in initial radiation.

The strength of a nuclear bomb is measured in terms if kilotons (1,000 tons of TNT). The power of a 10 kiloton bomb is equal to 10,000 tons of TNT. To carry that much explosives you would need a cargo train with 100 cars. The most powerful conventional weapons can only deliver about 1 percent of the of the power of the atomic bombs dropped on Hiroshima and modern hydrogen bombs are many times more powerful than the bomb dropped on Hiroshima.

Atomic Bomb Designs

Fission bomb assembly methods
Nuclear bombs are made with either plutonium or highly-enriched uranium. Around four kilograms (nine pounds) of plutonium or 15 kilograms (33 pounds) of highly-enriched uranium is necessary to make a nuclear bomb. Both materials are only available through nuclear weapons programs. Plutonium or highly-enriched uranium contain extraordinary amounts of energy: one gram of enriched uranium contains the energy potential of three tons of coal.

Obtaining weapons-grade nuclear materials is one of the biggest obstacles that has to overcome in making a nuclear bomb.The bomb dropped on Hiroshima was a gun-type uranium bomb in which critical mass was created with two-half-moon-shaped masses of uranium placed separately inside a tube that looks like a cannon barrel, with the two uranium masses combining into a sphere at the time of detonation. Implosion-technology described with plutonium bombs below can also be used to make atomic bombs with uranium.Uranium 235 is the uranium isotope used to make uranium-type nuclear bombs. Enrichment typically begins with gas that is 0.7 percent uranium 235. If purified to levels of around 5 percent the uranium can be used for nuclear power plants. If it is enriched to 90 percent it capable of creating the chain reaction for nuclear bombs.

Getting explosive material — in the form of weapons-grade, highly enriched uranium or weapons grade plutonium — is generally considered the hardest part of building a nuclear bomb. Uranium enrichment involves feeding UF6 gas — obtained from uranium ore — into centrifuges, machines made with a cylinder of superlight material that enriches materials by spinning them at supersonic speeds or around 70,000 times per minute. When uranium is spun at high speeds a small portion of the heavier uranium 238 drops away, increasing the proportion if Uranium 235. The process is repeating using thousands of centrifuges that are connected with complex and fragile connections. Any slight imperfection can cause the whole system to break down.

Plutonium Atomic Bomb Designs

To make a warhead using plutonium, plutonium metal is shaped into a sphere, as small as a grapefruit, and is surrounded with high explosives. When it detonated the explosives compress the plutonium to cause a nuclear chain reaction and a huge explosion. Plutonium is not suitable for a gun-type bomb because it tends to undergo premature chain reactions in the tube.

A simple implosion-style nuclear devices like the one used at Nagasaki contains nuclear material placed in a special casing in the bomb. Nuclear fission is caused by conventional weapons placed around the sphere that detonate simultaneously at the time of detonation, shrinking the mass into a smaller shape, but a high enough density to set off the chain reaction.

This type of bomb works by following six steps. 1) Explosives are fired at precisely the same time creating an inward-directed spherical shock wave. 2) Subcritical masses of uranium-235 are blasted together into a much denser, small ball of supercritcal mass. 3) An igniter pellet made of beryllium/plutonium breaks open releasing a burst of neutrons into the supercritcal mass of uranium-235. 4) The fission reaction starts when a neutron strikes a uranium nucleus, splitting it in two; 5) As the nucleus divides into two smaller nuclei it releases two or three neutrons that continue the process in a chain reaction releasing massive amounts of heat and radiation. 6) Only after all the uranium has been "burned" will the bomb explode. [Source: Newsweek]

Gun-Type Fission Weapon

Because implosion type techniques require less nuclear material to create critical mass than a gun-type bomb it is more suitable for making a smaller and lighter bombs mounted on a warhead. Plutonium is made by bombarding uranium in a nuclear reactor and then separating out the uranium with baths of acid. To make one kilogram of plutonium takes a thousand tons of uranium ore.

To obtain the plutonium for a nuclear devise from the spent fuel rods at a nuclear power plant: 1) an organic solvent is added to separate uranium and plutonium from the waste water by-products; 2) the liquid uranium and plutonium are separated and processed to create uranium oxide, a powder, and plutonium metal; 3) at a foundry the plutonium medal is shaped into a sphere as small as a grapefruit. To make a warhead, high explosives are placed around the sphere. When detonated the explosives compress the plutonium to cause a nuclear reaction and massive explosion equal to many thousands of tons of TNT.

Events Leading to the Development of the Atomic Bomb

In December 1938 scientists Otto Hahn, Fritz Strassmann and Lise Meitner discovered nuclear fission — the release of massive amounts of energy when the nucleuses of radioactive uranium atoms are bombarded with neutrons. Plutonium, which also releases massive amounts of energy when bombarded with neutrons, was discovered in 1941.

Leo Szilard, a Hungarian emigre physicist in the United States, is credited with being the first man to realize the destructive power of an atomic bomb. In 1939, he wrote a letter signed by Albert Einstein that was given to President Franklin Roosevelt about the possibility of creating a fission bomb with unimaginable destructive power.

In the fall of 1939 British intelligence officers were informed that Germany was experimenting with military applications of nuclear energy. On October 11, 1939, Churchill sent an intermediary to warn President Roosevelt that the construction of an atomic bomb was possible. Britain had been working on its own nuclear device. After the bombing of Pearl Harbor, the British sent all the their scientists to the U.S. to work with American scientists on a nuclear device.

The breakthrough that made atomic weapons possible came in December 1942 when a team lead by Enrico Fermi achieved the first controlled, self-sustained nuclear chain reaction in a squash court at the University of Chicago.

The fears that the Germans were further along in the development of an atomic bomb than the Allies proved to be unfounded but nevertheless these fears were what pushed the project forward at a lightning pace.

Implosion nuclear weapon

Atomic Bomb: Plans and Preparations

Henry Lewis Stimson, the Secretary of War under U.S. Presidents Roosevelt and Truman, wrote in Harper’s Magazine: “It was in the fall of 1941 that the question of atomic energy was first brought directly to my attention. At that time President Roosevelt appointed a committee consisting of Vice President Wallace, General Marshall, Dr. Vannevar Bush, Dr. James B. Conant, and myself. The function of this committee was to advise the President on questions of policy relating to the student of nuclear fission which was then proceeding both in this country and in Great Britain. [Source: Henry Lewis Stimson, Harper’s Magazine, February 1947; Asia for Educators Columbia University, Primary Sources with DBQs, ]

“For nearly four years thereafter I was directly connected with all major decisions of policy on the development and use of atomic energy, and from May 1, 1943, until my resignation as Secretary of War on September 21, 1945, I was directly responsible to the President for the administration of the entire undertaking; my chief advisers in this period were General Marshall, Dr. Bush, Dr. Conant, and Major General Leslie R. Groves, the officer in charge of the project. At the same time I was the President’s senior adviser on the military employment of atomic energy.

“The policy adopted and steadily pursued by President Roosevelt and his advisers was a simple one. It was to spare no effort in securing the earliest possible successful development of an atomic weapon. The reasons for this policy were equally simple. The original experimental achievement of atomic fission had occurred in Germany in 1938, and it was known that the Germans had continued their experiments. In 1941 and 1942 they were believed to be ahead of us, and it was vital that they should not be the first to bring atomic weapons into the field of battle. Furthermore, if we should be the first to develop the weapon, we should have a great new instrument for shortening the war and minimizing destruction. At no time, from 1941 to 1945, did I ever hear it suggested by the President, or by any other responsible member of the government, that atomic energy should not be used in war. All of us of course understood the terrible responsibility involved in our attempt to unlock the doors to such a devastating new weapon; President Roosevelt particularly spoke to me many times of his own awareness of the catastrophic potentialities of our work. But we were at war, and the work must be done. I therefore emphasize that it was our common objective, throughout the war, to be the first to produce an atomic weapon and use it. The possible atomic weapon was considered to be a new and tremendously powerful explosive, as legitimate as any other of the deadly explosive weapons of modern war. The entire purpose was the production of a military weapon; on no other ground could the wartime expenditure of so much time and money have been justified.

Manhattan Project sites

“The exact circumstances in which that weapon might be used were unknown to any of us until the middle of 1945, and when that time came... the military use of atomic energy was connected with larger questions of national policy...As time went on it became clear that the weapon would not be available in time for use in the European Theater, and the war against Germany was successfully ended by the use of what are now called conventional means. But in the spring of 1945 it became evident that the climax of our prolonged atomic effort was at hand. By the nature of atomic chain reactions, it was impossible to state with certainty that we had succeeded until a bomb had actually exploded in a full-scale experiment; nevertheless it was considered exceedingly probable that we should by midsummer have successfully detonated the first atomic bomb. This was to be done at the Alamogordo Reservation in New Mexico. It was thus time for detailed consideration of our future plans. What had begun as a well.founded hope was now developing into a reality.”

Manhattan Project, the Building of the Bomb

In September 1942 the ultra-secret Manhattan project was established in Los Alamos, New Mexico to make a nuclear device a reality. Almost 200,000 people worked on the $2 billion ($20 billion in today's money) project in the 37 secret plants and laboratories, including some of world's greatest minds — Nobel prizing winning physicist Niels Bohr, German refugee Klaus Fuchs, Italian emigre Enrico Fermi, and the charismatic director of the Los Alamos lab, Robert Oppenheimer. One journalist called them "the greatest collection of eggheads ever."

Oppenheimer was the scientific director of the project (the director was Army General Leslie Grove). As a boy Oppenheimer entertained himself by reading Plato in Greek. He graduated from Harvard in three years summa cum laude and got a Ph.D. in theoretical physics from the University of Göttingen in Germany. During the making of the bomb Oppenheimer shrunk to 115 pounds and developed a nasty hack from smoking so much. Later he was harassed by the McCarthy commission because a former girlfriend and his brother had been Communist party members. Oppenheimer himself briefly belonged to a Communist organization when he was a university student.

Most of atomic research and development for the Manhattan Project was done at Oak Ridge National Laboratory, near Knoxville, Tennessee (where uranium was enriched); Hanford, Washington (where plutonium was produced) and Los Alamos, New Mexico (where the Little Boy and Fat Man bombs were assembled). These labs are still open are involved in “developing pioneering technologies used for Mars exploration, chemotherapy, whole-body X-ray scanning at airports, high-speed computers and biotechnology.” [Source:Darryl Fears, Washington Post, July 28, 2012]

1st page of the Letter by Einstein to President Roosevelt in 1939 on the threat of nuclear weapons

Darryl Fears wrote in the Washington Post, “America’s race with Nazi Germany to develop the first atomic bomb received its code name, the Manhattan Project, in late 1941. The establishment of the Manhattan Engineering District followed in August 1942. Also in 1942, the Hanford reservation, along the Columbia River in eastern Washington, was selected to produce plutonium. The Oak Ridge and Los Alamos labs were established in 1943. In all, 125,000 people worked on the project at those sites and in Manhattan, but only about 1,000 knew the exact purpose of the work. About 32,000 people work at the two labs and Hanford now.

“At the program’s peak, 75,000 people worked on the Manhattan Project at Oak Ridge. Sixty cents of every dollar for the project was spent there.” Oak Ridge embraced the mile-long K-25 building, one of the largest in the world during the war. Today in the old control room you can see a logbook that recorded the time when the reactor first went critical, about 5 a.m. Nov. 4, 1943. Los Alamos still has the modest house that was once occupied by Oppenheimer.

When Harry Truman became President of the United States on April 12, 1945 after the death of Franklin Roosevelt he wasn't even aware of the atomic bomb's existence. He was briefed about the secret weapon by Groves, the head of the Manhattan Project, who later boasted that Truman was coerced into going along for the ride "like a little boy on a toboggan."

It cost more to build the first three nuclear bombs than it did to send men to the moon. Among the new technologies created to make atomic bombs possible were electrical detonators with microsecond timing, high explosives shaped into lenses that focused the shock waves to compress solid metal, cameras that worked at a million frames a second and the metallurgy of plutonium. The uranium used in the Manhattan project came from northwest Canada on the traditional lands of the Dene tribes, who had no idea what minerals on their land was being used for.

First Test of the Atomic Bomb

preparation for first nuclear test

The first test of an atomic bomb took place at Almagordo, New Mexico at 5:30am, on July 16, 1945. Before the bomb was exploded some of the Manhattan Project scientist weren't even sure it was going to work, and if it did work how big the explosion would be. A poem circulating around the New Mexico laboratory where the bomb was made went:
"From this crude lab that spawned a dud
Their necks to Truman's ax uncurled
Lo, the embattled savants stood
And fired the flop heard' round the world"

The bomb set off at Almagordo was like the Fat Man dropped on Nagasaki. Scientist placed bets on how big the blast would be. Some scientist predicted that the punch delivered by the atomic bomb would only be around 200 tons of TNT. Oppenheimer bet a modest 3,000 tons. Enrico Fermi jokingly asked anyone if they were willing to bet the bomb would ignite the atmosphere and blow up New Mexico. Isador Rabi won with bet with an estimate of 18,000 tons.

When the explosion thrust itself straight up, producing eery blue, red and green light and a signature mushroom cloud, instruments registered a blast of between 15,000 and 20,000 tons of TNT. The explosion produced a blinding light like "several suns at midday" that was strong enough to reflect off the moon. A shock wave generated by the blast broke a window 125 miles away. Upon witnessing the fireball, Oppenheimer remembered a line from Hindu scripture: "I am become Death, the shatterer of worlds." After the test he said: “We knew the world would not be the same.”

Upon hearing that the first Atomic bomb had been exploded at Almagordo, Churchill told the American Secretary of War: "This Atomic Bomb is the Second Coming in Wrath!" Truman wrote in his diary, "We have discovered the most terrible bomb in the history of the world. It may be the fire prophesied in Euphrates Area after Noah and his famous Ark...It is certainly a good thing for the world that Hitler's crowd or Stalin's did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful. “

Nuclear testing had its share of victims. A man who lived downwind from a nuclear testing site in Nevada told National Geographic: “one day I was out cutting hay, and there was this blueish gray haze in the air. The sweat on my arms and face felt like stinging nettles, and I had to take a rag and keep wiping it off, because it burned so bad. By the time I was 18 I had thyroid cancer.”

Report of First Test of the Atomic Bomb

Trinity Explosion

Two days after the blast, Gen. Groves, sent a Top Secret memorandum to Secretary of War Stimson detailing the test. Groves included the description of Gen. Thomas Farrell who was in an observation hut close to the blast along with some scientists and other personnel. He reported: "The scene inside the shelter was dramatic beyond words. In and around the shelter were some twenty-odd people concerned with last minute arrangements prior to firing the shot. Included were: Dr. Oppenheimer, the Director who had borne the great scientific burden of developing the weapon from the raw materials made in Tennessee and Washington and a dozen of his key assistants - Dr. Kistiakowsky, who developed the highly special explosives; Dr. Bainbridge, who supervised all the detailed arrangements for the test; Dr. Hubbard, the weather expert, and several others. Besides these, there were a handful of soldiers, two or three Army officers and one Naval officer. The shelter was cluttered with a great variety of instruments and radios. [Source: Department of State, Foreign Relations for the United States Conference of Berlin (Potsdam) (1945); Lansing, Lamont, Day of Trinity (1965).

For some hectic two hours preceding the blast, General Groves stayed with the Director, walking with him and steadying his tense excitement. Every time the Director would be about to explode because of some untoward happening, General Groves would take him off and walk with him in the rain, counseling with him and reassuring him that everything would be all right. At twenty minutes before zero hour, General Groves left for his station at the base camp, first because it provided a better observation point and second, because of our rule that he and I must not be together in situations where there is an element of danger, which existed at both points.

Just after General Groves left, announcements began to be broadcast of the interval remaining before the blast. They were sent by radio to the other groups participating in and observing the test. As the time interval grew smaller and changed from minutes to seconds, the tension increased by leaps and bounds. Everyone in that room knew the awful potentialities of the thing that they thought was about to happen. The scientists felt that their figuring must be right and that the bomb had to go off but there was in everyone's mind a strong measure of doubt. The feeling of many could be expressed by ''Lord, I believe; help Thou mine unbelief.' We were reaching into the unknown and we did not know what might come of it. It can be safely said that most of those present - Christian, Jew and Atheist - were praying and praying harder than they had ever prayed before. If the shot were successful, it was a justification of the several years of intensive effort of tens of thousands of people statesmen, scientists, engineers, manufacturers, soldiers, and many others in every walk of life.

Crater from first nuclear test

In that brief instant in the remote New Mexico desert the tremendous effort of the brains and brawn of all these people came suddenly and startlingly to the fullest fruition. Dr. Oppenheimer, on whom had rested a very heavy burden, grew tenser as the last seconds ticked off. He scarce breathed. He held on to a post to steady himself. For the last few seconds, he stared directly ahead and then when the announcer shouted 'Now!' and there came this tremendous burst of light followed shortly thereafter by the deep growling roar of the explosion, his face relaxed into an expression of tremendous relief. Several of the observers standing back of the shelter to watch the lighting effects were knocked flat by the blast.

The tension in the room let up and all started congratulating each other. Everyone sensed 'This is it!' No matter what might happen now all knew that the impossible scientific job had been done. Atomic fission would no longer be hidden in the cloisters of the theoretical physicists' dreams. It was almost full grown at birth. It was a great new force to be used for good or for evil. There was a feeling in that shelter that those concerned with its nativity should dedicate their lives to the mission that it would always be used for good and never for evil.

Dr. Kistiakowsky, the impulsive Russian, [actually an American and a Harvard professor] threw his arms around Dr. Oppenheimer and embraced him with shouts of glee. Others were equally enthusiastic. All the pent-up emotions were released in those few minutes and all seemed to sense immediately that the explosion had far exceeded the most optimistic expectations and wildest hopes of the scientists. All seemed to feel that they had been present at the birth of a new age - The Age of Atomic Energy - and felt their profound responsibility to help in guiding into right channels the tremendous forces which had been unleashed for the first time in history. As to the present war, there was a feeling that no matter what else might happen, we now had the means to insure its speedy conclusion and save thousands of American lives."

Deployment of the Atomic and the Choice of Hiroshima and Nagasaki as Targets

20120710-nuclear plutonu94.jpg

On July 26, the Hiroshima Little Boy bomb was loaded on the U.S. warship Indianapolis to be taken to the island of Tinian. On that same day the Allies gave the Japanese the Potsdam Declaration, stating that "to end the war...we call upon the government of Japan to proclaim now the unconditional surrender of all Japanese armed forces...The alternative for Japan is prompt and utter destruction." At a press conference, Japan's Prime Minister Kantaro Suzuki said that his government planned to ignore the declaration and "resolutely fight for the successful conclusion of the war."

On July 30, after a meeting with his closest advisers, Truman ordered the atomic bombing of Hiroshima with the transmission: "Suggestion approved. Release when ready." The deployment was delayed several days by a typhoon.

Director of the Manhattan Project, Army General Leslie Grove, had originally wanted to drop an atomic bomb on the ancient capital of Kyoto, with it hundreds of shrines and temples, because he regarded it as the "intellectual center" of Japan and he wanted to bomb a place that "would most adversely affect the will of the Japanese people to continue the war." Secretary of War Henry Stimson, who had visited Kyoto in the 1920s, overruled Groves, arguing that destroying Japan's cultural capital was wrong. Niigata, another city that survived the firebombing raids, was another city on the shortlist of targets because it was still largely unscathed.

Hiroshima was by no means just a civilian target. It was Japan's western military capital and home of massive munitions factories and Japan's second largest military school.. There was a military headquarters in the middle of town; factories churned out large amounts of military hardware; and the Mitsubishi Heavy Industries shipyard was one of the major builders of giant warships. Hiroshima’s port on the Inland Sea was the staging area for military action in China, Korea and Southeast Asia. Before the atomic bomb was dropped Hiroshima had not been bombed at all. Some people have suggested that this was done on purpose to measure the destructive power of the bomb.

20120710-nuclear Plutonium_ring.jpg
Plutonium ring
Hiroshima was home to around 250,000 people at the time the bomb was dropped. It was selected in part because it had a large industrial complex surrounded by densely populated residential areas and it was thought to have no prisoner-of-war camps. One advisor, suggested that the “the most desirable target would be a vital war plant employing a large number of workers and closely surrounded by worker’s houses.” Many of the people who worked in the factories were Chinese and Koreans forced to work in Japan.

Nagasaki was originally the secondary target and the only reason it was bombed was that the primary target was covered in clouds. The plane flew over the main target, Kokura (present-day Kitakyushu) three times without finding a target before take off for Nagasaki, which was not far away. Nagasaki was also covered by clouds but a gap opened up and the Mitsubishi Arms Work was sighted and became the target. After the bomb was dropped the plane flew to Okinawa, its tanks almost empty of fuel.

Riding in plane behind the plane carrying the Nagasaki bomb, William T. Lawrence wrote of the New York Times on August 9, 1945: "The winds of destiny seemed to favor certain Japanese cities...We circled about them again and again and found no opening in the thick umbrella of clouds that covered them. Destiny chose Nagasaki as the ultimate target."

Image Sources: National Archives of the United States; Wikimedia Commons; Gensuikan;

Text Sources: National Geographic, Smithsonian magazine, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Yomiuri Shimbun, The New Yorker, Lonely Planet Guides, Time, Newsweek, Reuters, AP, AFP, Wikipedia, BBC, “Eyewitness to History “, edited by John Carey ( Avon Books, 1987), Compton’s Encyclopedia, “History of Warfare “ by John Keegan, Vintage Books, Eyewitness to, “The Good War An Oral History of World War II” by Studs Terkel, Hamish Hamilton, 1985, BBC’s People’s War website and various books and other publications.

Last updated November 2016

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