1931
Heavy hydrogen or deuterium is discovered by Harold C. Urey.
On August 6, 1945, during World War II (1939-45), an American B-29 bomber dropped the world's first atomic bomb, the "little boy" over the city of Hiroshima, Japan under the Harry Trueman's order. The bomb immediately killed an estimated amount of 80,000 people, and thousands more would die of radiation, Three days later, on August 9, 1945, another American B-29 bomber dropped a second atomic bomb on Nagasaki which killed an estimated 40,000 people. These remain the only two instances of nuclear weapons being used in warfare to this day. While the war in Europe ended on May 8, 1945, as a result of the atomic bombing of these two major cities, Japan's Emperor Hirohito announced his country's unconditional surrender in World War II in a radio address on August 15, 1945. The atomic bombing of Japan was a hugely significant final act of the most destructive global conflict in human history. Simultaneously, it signaled the dawn of the atomic age, the arms race between the US and the Soviet Union, and - before too long - the cold war.
To answer this question, it is helpful to define some central chemical principles. Labelled atom. Shutterstock An atom is the basic unit of matter. The nucleus of an atom is made of smaller particles called protons and neutrons. Other atomic particles called electrons surround the nucleus. Elements are the simplest chemical substances and consist of atoms that all have the same number of protons. In the 1930s, scientists showed that nuclear energy could be released from an atom, either by splitting the nucleus (fission) or fusing two smaller atoms to form a larger one (fusion). As the second world war erupted, intense research focused on how to artificially induce nuclear fission by firing a free neutron into an atom of radioactive uranium or plutonium. Through their efforts, scientists found a way to induce a chain reaction within a bomb that would generate an unprecedented amount of energy.
Even before the outbreak of war in 1939, a group of American scientists-many of them refugees from fascist regimes in Europe-became concerned with nuclear weapons research being conducted in Nazi Germany. In 1940, the U.S. government began funding its own atomic weapons development program, which came under the joint responsibility of the Office of Scientific Research and Development and the War Department after the U.S. entry into World War II. The U.S. Army Corps of Engineers was tasked with spearheading the construction of the vast facilities necessary for the top-secret program, codenamed "The Manhattan Project" (for the engineering corps' Manhattan district). Over the next several years, the program's scientists worked on producing the key materials for nuclear fission-uranium-235 and plutonium (Pu-239). They sent them to Los Alamos, New Mexico, where a team led by J. Robert Oppenheimer worked to turn these materials into a workable atomic bomb. Early on the morning of July 16, 1945, the Manhattan Project held its first successful test of an atomic device-a plutonium bomb-at the Trinity test site at Alamogordo, New Mexico.
Heavy hydrogen or deuterium is discovered by Harold C. Urey.
The atom is split by John Crockcroft and E.T.S. Walton of Great Britain, thereby proving Einstein's Theory of Relativity.
Hungarian physicist Leo Szilard realizes the possibility of the nuclear chain reaction.
Fermi achieves first nuclear fission.
The Theory of Nuclear Fission is announced by Lise Meitner and Otto Frisch.
At a conference at George Washington University, Niels Bohr announces the discovery of fission.
Robert Oppenheimer realizes the military possibilities of nuclear fission.
Einstein writes to President Roosevelt concerning the use of uranium as a new source of energy leading to the formation of the Committee on Uranium.
World War II begins.
Plutonium is discovered by Glenn Seaborg , Edwin McMillan, Joseph W. Kennedy, and Arthur Wahl.
FDR gives the go-ahead for the development of an atomic weapon.
Manhattan Engineering District is established for the purpose of creating an atomic bomb. This would later be called the "Manhattan Project."
Col. Leslie Groves is placed in charge of the Manhattan Project. Oppenheimer becomes the project's scientific director.
Fermi produces the first controlled nuclear fission reaction at the University of Chicago.
Japan becomes the primary target for any future atomic bomb according to the Military Policy Committee of the Manhattan Project.
Roosevelt dies. Harry Truman is named the 33rd president of the U.S.
The Target Committee of the Manhattan Project selects four cities as possible targets for the atomic bomb: Kyoto, Hiroshima, Kokura, and Niigata.
War ends in Europe.
Szilard attempts to warn Truman in person concerning the dangers of atomic weapons.
Szilard begins a petition to get Truman to call off using the atomic bomb in Japan.
American intelligence discovers the only obstacle to peace with Japan is "unconditional surrender."
The world's first atomic detonation takes place in the Trinity Test at Alamogordo, New Mexico.
Truman orders atomic bombs to be used.
Potsdam Declaration is issued, calling for the '"unconditional surrender of Japan."
Japan rejects Potsdam Declaration.
Little Boy, a uranium bomb, is detonated over Hiroshima, Japan. It kills between 90,000 and 100,000 people immediately.
U.S. decides to drop warning pamphlets on Japanese cities.
The second atomic bomb to hit Japan, Fat Man, was scheduled to be dropped at Kokura. However, because of poor weather, the target was moved to Nagasaki. Truman addresses the nation.
U.S. drops warning leaflets concerning another atomic bomb on Nagasaki, the day after the bomb was dropped.
Japan announces its formal surrender.
Edward Teller approaches Oppenheimer to aid in the building of a new hydrogen bomb. Oppenheimer refuses.
An atomic bomb causes massive destruction through intense heat, pressure, radiation and radioactive fallout. At the hypocentre (centre of the blast), the heat is so intense, it vaporises people and buildings. Between 60,000-80,000 people were killed instantly when the bomb detonated over Hiroshima and an estimated 140,000 died from acute effects of the bomb before the end of the year. The death toll increased to over 200,000 people in subsequent decades, as people died from cancers and other diseases linked to radiation poisoning.In addition to the human toll, almost 63% of Hiroshima’s buildings were destroyed and a further 29% damaged by the bomb. The Genbaku (Atomic Bomb) Dome was the only building left standing near the hypocentre. Today, it is preserved at the Peace Memorial Park and the city has been rebuilt around it. The total death toll in Nagasaki was lower in comparison, as parts of the city were shielded by mountains. Still, at least 75,000 people died there in total. Nagasaki receives less attention in analysis of the bombings, despite being the last place a nuclear weapon was used in warfare. Hibakusha - the Japanese term for explosion-affected people - continue to campaign for Nagasaki to retain its sad distinction.
Official A-Bomb Justification: Save US Lives
According to Truman and others in his administration, the use of the atomic bomb was intended to cut the war in the Pacific short, avoiding a U.S. invasion of Japan and saving hundreds of thousands of American lives.
In early 1947, when urged to respond to growing criticism over the use of the atomic bomb, Secretary of War Henry Stimson wrote in Harper's Magazine that by July 1945 there had been no sign of "any weakening in the Japanese determination to fight rather than accept unconditional surrender." Meanwhile, the U.S. was planning to ramp up its sea and air blockade of Japan, increase strategic air bombings and launch an invasion of the Japanese home island that November.
"We estimated that if we should be forced to carry this plan to its conclusion, the major fighting would not end until the latter part of 1946, at the earliest,” Stimson wrote. “I was informed that such operations might be expected to cost over a million casualties, to American forces alone.”
The Other Reason? Get the Soviet Union's Attention
Despite the arguments of Stimson and others, historians have long debated whether the United States was justified in using the atomic bomb in Japan at all—let alone twice. Various military and civilian officials have said publicly that the bombings weren't a military necessity. Japanese leaders knew they were beaten even before Hiroshima, as Secretary of State James F. Byrnes argued on August 29, 1945, and had reached out to the Soviets to see if they would mediate in possible peace negotiations. Even the famously hawkish General Curtis LeMay told the press in September 1945 that “the atomic bomb had nothing to do with the end of the war at all.”
Statements like these have led historians such as Gar Alperovitz, author of The Decision to Use the Atomic Bomb, to suggest that the bomb’s true purpose was to get the upper hand with the Soviet Union. According to this line of thinking, the United States deployed the plutonium bomb on Nagasaki to make clear the strength of its nuclear arsenal, ensuring the nation's supremacy in the global power hierarchy.
https://www.archives.gov/news/topics/hiroshima-nagasaki-75
https://www.iwm.org.uk/history/the-atomic-bombs-that-ended-the-second-world-war
https://www.khanacademy.org/humanities/us-history/rise-to-world-power/us-wwii/a/the-manhattan-project-and-the-atomic-bomb
https://www.atomicarchive.com/history/atomic-bombing/nagasaki/page-7.html
