November, 1931 - Deuterium discovered by Urey.
February, 1932 - Neutron discovered by Chadwick. (Existence of which was predicted by Rutherford).
December, 1934 - Artificial radioactivity discovered by Joliot-Curie [with alpha particles] and Fermi when he irradiated uranium with neutrons and produced the first transuranic element(and first fission reaction, though unknowingly at a time).
December, 1938 - Fermi receives a Nobel prize for discovering transuranic elements. Otto Hahn and Fritz Strassmann split the uranium atom by bombarding it with neutrons, producing the elements Barium and Krypton.
1939 - Hans A. Bethe creates theory about nuclear fusion. He suggested that much of the energy that the Sun and other stars produce is the result from reactions in which four hydrogen nuclei unite, forming one Helium nucleus while releasing a large amount of energy.
August, 1939 - Albert Einstein sends a letter to President Franklin Roosevelt. In this message, he warns the president, that Nazi Germany is attempting to build a new weapon, which would be more powerful and more destructive than any weapon ever known to mankind. That weapon is an Atomic Bomb. Practically the letter didn't have any influence, only after Pearl Harbor bombing by Japanese, US goverment made serious corrections to his "nuclear strategy" which eventually formed as Manhattan project. The letter is studied by masters in political science as a main example of how science and politics converged in the 20th century.
September 17, 1942 - Although the Manhattan Project was officialy founded in August the real start was this day, when Col. Leslie Richard Groves got his assigmenet on this project.
July 16, 1945 - The first nuclear explosion, conducted by US, in Almagordo, New-Mexico, during the Trinity test, the device code named Gadget was detonated on the tower yielded 19 Kt and used Pu239. That was the logical end of 20 Billion cost Manhattan project.
August 06, 1945 - US exploded nuclear bomb over Hiroshima, Japan. The U235 gun-type bomb named Little Boy, detonated at 8:16:02 a.m. at an altitude of 1900 ft. In an instant 80,000 to 140,000 people were killed and 100,000 more were seriously injured. Yield 15Kt. Delivered by B29 Bomber Enola Gay.
August 09, 1945 - US exploded nuclear bomb over Nagasaki, Japan. The bomb named Fat-Man(special thanks to Lino for the cool pic:) was detonated at 11:02 am. at an altitude of 1500 ft. Fat Man used Pu239 instead U235 and it was more efficient, implosion type design. Of the 286,000 people living in Nagasaki at the time of the blast, 74,000 were killed and another 75,000 sustained severe injuries. Yield 21Kt. Delivered by B29 Bomber Bock's Car.
August 29, 1949 - USSR detonated his first nuclear bomb Joe-1, detonation at the Semipalatinsk test site. Yielded 22 Kt.
May 8, 1951 - During the operation Greenhouse US exploded the first fusion device called George on the atoll Enwetak. This was not a real bomb that could be delivered by an airplane or missile. Yielded 225 Kt.
October 3, 1952 - UK first nuclear detonation. Monte-Bello islands, Australia. The bomb called Hurricane was detonated on the ship.
October 31, 1952 - US exploded the first real H-bomb. During the operation Ivy, Mike shot yielded 10.4 Mgt. Surface explosion.
August 12, 1953 - USSR detonated his first fusion bomb, called Joe-4, on the tower, yielded 300 Kt.
March 1, 1954 - During the operation Castle on the Bikini atol, US detonated the thermonuclear bomb Bravo. Yield 15 Mgt. It became largest thermonuclear device ever detonated by US. Bravo was the first Teller-Ulam design, where Lithium deuteride was used as a fuel. Subsequently, that became a standard for all thermonuclear weapon designs, including USSR nuclear weapons. Interestingly, the projected yield of the Bravo was only 4-6 Mgt. However during the explosion, unpredicted, large amount of tritium was formed because of the fast neutron fission of Li7, which in turn increased the yield by some 250%. Unfortunately, Bravo explosion created significant rediological problems around the testing area, and is still studied by experts.
February 13, 1960 - France detonated his first nuclear bomb in Algeria, Reggane Proving Grounds, this bomb - G Bleue yielded 70 Kt.
January 24, 1961 - Abother broken arrow. A B-52 strategic bomber flying from Saymore Johnson AFB suffers structural failure over North Carolina. 2 high yield, unarmesd thermonuclear weapons are released as a result. Parachute deploys on one bomb, which lands safely on the tree, receiving very little impact. Upon recovery examinators discovered that 5 out of 6 safety devices have failed. Realizing that only a single switch prevented unprecendented nuclear disaster, strategic command proceeds to install additional safety devices on all US nuclear weapons. Soviets were encouraged to follow as well.
October 30, 1961 - USSR broke the moratorium on the nuclear tests and conducted the biggest explosion of the thermonuclear device. The bomb called "Tzar Bomba" was air delivered (by Tu-95 Bear) and exploded in the atmosphere over the "Novaya Zemlya", (island in northern part of Russia, its name translates - something like "New land" ) yielded 50 Mgt. For more info click here
June 20, 1963 - U.S./U.S.S.R. sign 'hot line' agreement.
August 5, 1963 - Limited Test Ban Treaty signed.
October 16, 1964 - China detonated his first nuclear bomb called "596", that yielded 22Kt.
January 17, 1966 - U.S. B-52 bomber crashes near Palomares, Spain with 4 unarmed H-bombs. Recovered later, successfully.
September 24, 1966 - France detonated his first H-bomb, Tuamoto Islands.
June 17, 1967 - China detonated his first H-Bomb during the operation codenamed Test No. 6. Yield 3.3 Mgt.
May 18, 1974 - India detonates his first nuclear bomb, that yields 15 Kt.
May 11, 1998 - India detonates 3 nuclear devices. By indian officials version 1
thermonuclear and 2 nuclear devices were detonated.
The device that Indian goverment climed to be "Thermonuclear" was not an actual H-Bomb. In fact it was a boosted nuclear bomb and produced yield of approx. 43 Kt.
Second device detonated that day was a fission bomb and it yelded 12 Kt, third one yielded < 1Kt.
On may 13 India detonated 2 more nuclear devices with total yield < 1 Kt.
May 28, 1998 - Pakistan officials claimed to have detonated five simultaneous nuclear tests. All of them - boosted devices made with highly enriched Uranium. According to Pakistan a total yield was in the range of 40 to 45 kilotons. India disagrees :) suggesting slightly different number - 10 to 15 kilotons. Using seismic information, U.S. intelligence has confirmed only two nuclear explosions on may 28, yield - 6 kilotons. Pakistan detonated an additional nuclear device two days later, on May 30. claiming that the yield was in the range of 15-18 kilotons, but U.S. intelligence disagreed, bringing the 2 Kt. estimate.