| March 1930 | [U.S.A.] Pluto discovered by C.W. Tombaugh. (see plutonium) |
| 1930 | [Germany] Discovery of radiation which penetrates a leadblock by Walter Bethe. (Received 1954 Nobel prize.) |
| 18.1.1932 | [France] Proton emission from beryllium irradiated by alpha-ray,discovered by Frederick Joliot and Irene Curie. |
| 27.2.1932 | [England] Neutron discovered by James Chadwick, verifying Rutherford's Baker Lecture. (Received 1935 Nobel prize.) |
| February 1932 | [U.S.A.] Cyclotron developed by Ernest Orlando Lawrence and M.S. Livingston of California University, 27.5 inch size developing one million electron volts. (Received 1939 Nobel prize) |
| April 1932 | [England] Conversion of element by John Douglas Cockcroft and Ernest Thomas Sinton Walton. Emergence of helium by irradiating high-speed proton to lithium, based on Gamow's tunnel effect. (Received 1951 Nobel prize) |
| 2.8.1932 | [U.S.A.] Positron discovered by Carl David Anderson, detecting a cosmic-ray shower using a cloud chamber. (Received 1936 Nobel prize) |
| 1932 | [U.S.A.] Deuterium discovered by Harold Clayton Urey. (Received1934 Nobel prize) |
| 9.9.1933 | Albert Einstein moves to England. |
| 1933. 9.12 | [England] Idea of chain reaction via neutron by L.Szilard. He took a hint on the Times' report of Rutherford's lecture about atomic transition. The idea of atomic bomb was patented in 1934. The patent was transferred in secret to England's navy in February 1936. |
| 1933.10. 7 | Albert Einstein moves to U.S.A. |
| October 1933 | The 7th Solvay meeting. M. Curie, E. Rutherford, N. Bohr, L. Meitner, W. Heisenberg, W. Pauli, E. Fermi, J. Chadwick, G. Gamow, F. and I. Curie, P.M.S. Blackett, R.E. Peierls. In Brussels which was on the structure of the proton. |
| December 1933 | [Italy] Weak interaction and beta-decay theory by Enrico Fermi. (Received 1938 Nobel prize.) |
| 15.1.1934 | [France] Artificial radioactivity. F. and I. Curie detected radioactive phosphorus and positron by means of a Geiger counter after irradiating aluminum with alpha-rays from polonium. Blessed by M.Curie who was suffering from leukemia caused by irradiation. ( Recieved 1935Nobel prize) |
| 10.5.1934 | [Italy] Transuranic elements assumed by E.Fermi based on experimental results of irradiation of proton from radon and beryllium to uranium |
| September 1934 | [Germany] Possibility of nuclear fission proposed by Ida Noddack, a feminine scientist, not attracting attention. |
| 22.10.1934 | [Italy] Radioactivity induced by slow neutrons discovered by E.Fermi. |
| 1935 | [Japan] Meson predicted by Hideki Yukawa. Pi meson is a hadron involved in alpha-decay and nuclear force. (Received 1949 Nobel prize.) |
| 27.1.1936 | [Denmark] Liquid-drop model of atomic nucleus proposed by Niels Bohr. |
| 1936 | [England] Energy production by conversion of hydrogen to helium proposed in a lecture by Francis William Aston. |
| 1937 | [U.S.A.] Cyclotron with 60 inches diameter and 220 tons magnet. Planned by E. Lawrence as a medical appliance, depending on private contribution. |
| 1938. 9 | [France] Radioactivity with a half life of 3.5 hr produced by neutron irradiation of uranium is from lanthanum, reported by I. Curieand Pavel Savitch. |
| 1938 | [U.S.A.] Uranium 235 and uranium238 (ratio of 1:139 in natural uranium), analyzed by Alfred Nier by means of Dempster's mass spectrometer. |
| 1938 | [Germany] Isotope-separating device developed by Klaus Cladius and G.Dicker employing a gas thermal diffusion method. |
| 19.12.1938 | [Germany] Uranium nuclear fission: Barium is detected by Otto Hahn and Fritz Strassmann after irradiation by neutron of uranium at Kaiser Wilhelm Institute. They asked L. Meitner's comments by a letter. Beginning of the Barium Fantasy. (Received 1944 Nobel prize.) |
| 6.1.1939 | [Denmark] A theoretical explanation of nuclear fission of uranium written by L.Meitner and Otto Frisch employing a liquid drop model and theory of relativity. Next day N. Bohr brought a copy of the paper to U.S.A. Conversion of one fifth of the mass of a proton to energy is plausible. |
| 13.1.1939 | [Denmark] Detection of uranium nuclear fission by a cloud chamber by Otto Frisch. Later nuclear fission of thorium was verified. Thorium nuclear fission is triggered with fast neutron. |
| 25.1.1939 | [U.S.A.] Verification of the uranium nuclear fission by means of an oscilloscope by Herbert Anderson, a student of Fermi. Emission of neutron by irradiating hydrogen with deuteron accelerated by means of cyclotron at Columbia University. Failure in previous experiment by Fermi in Rome was due to an obstruction by aluminum foils. |
| 26.1.1939 | [France] Verification of uranium nuclear fission by J. and I. Curie. They failed to detect neutron emission. |
| 26.1.1939 | [U.S.A.] The fifth Washington meeting sponsored by American Physics Society. N. Bohr, E. Fermi, Otto Stern, H.C. Urey, Gregory Bright, Issidor Isaac Rabi, G. Gamow, E. Teller, Merle Tuve. Lectures by N. Bohr and E.Fermi on the uranium nuclear fission called "splitters." |
| 28.1.1939 | [U.S.A.] Verification of uranium nuclear fission by Richard Roberts and Robert Meyer. Emission of neutron on irradiating lithium with neutron accelerated by a van de Graaff accelerator, was employed for irradiation of uranium. Demonstration to members in the Washington Conference. Delayed neutron was detected in later experiments, a discovery suggesting a possibility of reactor control. |
| 30.1.1939 | [U.S.A.] Verification of uranium nuclear fission by Phillip Abelson. Luis Walter Alvarez transferred the news of nuclear fission of uranium to Abelson. They found tellurium-52 and zirconium-40 as the fission products. J.R. Oppenheimer, as noted by Alvarez, predicted neutron emission and possibility of developing atomic bomb. |
| 7.2.1939 | [U.S.A.] Nuclear fission of 235uranium is caused@by slow neutron, a theory proposed by N. Bohr and John Archibald Wheeler. |
| 17.3.1939 | [U.S.A.] The first meeting on nuclear energy for military purposes. The first proposal by scientists (G.P. Pegram and E.Fermi) of the development of atomic bomb to Navy. E. Fermi talked on the controlled reaction by slow neutron, explosion by fast neutron and reaction in the supernova. |
| March 1939 | [France] More than one neutron emitted with nuclear fission of uranium observed by J. Curie, Hans Halban and Lew Kowarski. |
| March 1939 | [U.S.A.] About two neutrons emitted with nuclear fission of uranium verified independently by L.Szilard and Walter Zinn. |
| 22.4.1939 | [France] Number of neutrons emitted with nuclear fission of 235uranium is 3.5 /fission. Later corrected to 2.6/fission. By F.J.Curie, H.Halban and L.Kowarski. |
| 29.4.1939 | [Germany] A secret conference about a research program on the nuclear bomb in Berlin. A trade embargo on uranium and radium. Letter of Paul Harteck. |
| April 1939 | [U.S.A.] John Dunning's request to Alfred Nier to separate uranium235. |
| May 1935 | N. Bohr returns to Copenhagen in order to support refugee@scientists. |
| 3.7.1939 | [U.S.A.] Idea of nuclear reactor (pile) by E.Fermi and L.Szilard. Natural uranium as fuel and graphite as moderator of neutron energy. |
| 2.8.1939 | [U.S.A.] A letter of A.Einstein to President Roosevelt. L. Szilard, E. Teller and E. Wigner persuaded Einstein to warn President Roosevelt of German menace. The letter suggested the possibility of uranium bomb. |
| 1.9.1939 | World War II begins with the German invasion of Poland. Blitzkrieg by tanks. |
| 16.9.1939 | [Germany] A secret conference in Berlin on Bohr's paper about nuclear fission. |
| 26.9.1939 | [Germany] The second Berlin meeting. Start of German nuclear bomb project. Kurt Diepner, Erich Bagge, W. Heisenberg and Paul Harteck. |
| October 1939 | [England] An idea by J. Chadwick for an atomic bomb utilizing natural uranium based on a paper by R.Peierls, mass needed for critical state: 30-40 tons. |
| 6.12.1939 | [Germany] Report by W.Heisenberg of the possibility of a uranium bomb to Germany Department of War. |
| December 1939 | [U.S.A.] A discovery by Edwin Mattison McMillan of the existence of the radioactive substance that stays in uranium on nuclear fission experiment. |
| 1939 | [U.S.A.] A theory of energy production in stars by Hans Albrecht Bethe, the carbon cycle. (Received 1967 Nobel Prize.) |
| 1.2.1940 | [England] An idea by O. Frisch and E. Peierls of highly enriched uranium bomb presented in a 3 page memo describing the critical mass as 600 g. Presented via Mark Oliphant of Birmingham University to Henry T. Tizard. |
| 29.2.1940 | [U.S.A.] Separation of uranium235 by A. Nier. 1/1,000,000,000gr on a nickel film was sent to John R. Dunning in a letter. Uranium chloride (IV) or uranium fluoride (IV) was used. Minnesota University. |
| February 1940 | [U.S.A.] Uranium research budget of $6000 authorized: the purchase cost of graphite for E. Fermi and L. Szilard. |
| 2.3.1940 | [U.S.A.] Verification of uranium235 fission with slow neutron by J. Dunning (irradiation by a cyclotron of a sample separated by A. Nier. (Colombia University) |
| 9.4.1940 | [Germany] Invasion and occupation of Denmark. |
| 10.4.1940 | [England] George Paget Thomson committee. Small scale separation experiments utilizing uranium fluoride (VI) agreed. |
| 10.5.1940 | [U.S.A.] President Roosevelt's appeal for cooperation of The American Scientists Federation. E. Teller decides to participate in nuclear weapon research. |
| 27.5.1940 | [U.S.A.] A new 93rd element is discovered through irradiation of uranium oxide using neutrons accelerated by a cyclotron. Called Neptuniumby E.McMillan. (Received 1951 Nobel Prize) |
| 27.5.1940 | [U.S.A.] The possibility of nuclear fission of transuranic elements proposed by Louis A. Turner. |
| June 1940 | [France] H. Halban and L. Kowarski escape to England carrying180 L heavy water with all the data of J.Curie. An test of a chain reaction utilizing the heavy water carried out at the Cavendish Laboratory failed. |
| June 1940 | [England] A gas dispersion method experiment by Franz Simon utilizing a copper partition for separating vapor and carbon dioxide. |
| June 1940 | [Soviet Union] Uranium Committee established in Academy of Science by Igor Kurchatov. Interrupted due to German invasion in June,1941. |
| October 1940 | [Japan] Army commander Suzuki's report of the possibility of developing an atomic bomb based on a survey of uranium deposit in Chinese and Burma. |
| November 1940 | [U.S.A.] Start of experiment on gas dispersion method for enriching uranium-235 by H. Urey and J. Dunning. Uranium fluoride (VI) vaporizes at 56 deg C. |
| 15.12.1940 | [U.S.A.] Nuclear fission of the new element 94239 foreseen by E. Fermi and E. Segre. The possibility of a new element produced in a nuclear reactor. |
| 16.12.1940 | [U.S.A.] A new element 94239. A plan for production utilizing the 60-inchs cyclotron proposed by E. Lawrence, E. Segre, E. Fermi and G. Pegram. |
| 28.12.1940 | [England] A new idea of heavy water nuclear reactor by H. Halban. A method for separation of element 93, discovered by Pletcher was conveyed to U.S.A. |
| December 1940 | [England] A plan for a factory for separation of uranium235 by F. Simon. (MAUD committee, gas dispersion method.) |
| December 1940 | [England] A possibility of nuclear fission of new element94 reported to MAUD committee. |
| 1940 | [Soviet Union] Spontaneous fission of uranium discovered by George Flerov. |
| 1941 | [U.S.A.] P. Abelson moves to Navy Research Institute in order to develop a small size nuclear reactor for submarine. |
| 28.1.1941 | [U.S.A.] A new element 94238 discovered by E. Segreand Glenn T. Seaborg. Uranium oxide was irradiated by neutrons accelerated with a cyclotron. (Received 1951 Nobel prize.) |
| 23.2.1941 | [U.S.A.] New element 94 chemically separated as a solution by E. Segre, G. Seaborg and Arthur Wall. |
| 6.3.1941 | [U.S.A.] New element 94239 by irradiation of 1.2kg uranium oxide with neutrons emitted from beryllium irradiated by dnutrons.1 microgram of element was obtained. E. Segre and G. Seaborg. |
| 17.3.1941 | [U.S.A.] E. Lawrence proposes promotion of "uranium plan" based on conviction of the enriching method of uranium-235 utilizing cyclotron. |
| 28.3.1941 | [U.S.A.] Verification of nuclear fission of new element 94239 by E. Segre, G. Seaborg and Joseph Kennedy. Irradiation of new element 94 by paraffin-decelerated neutron emitted from beryllium irradiated by neutrons. About 1.5 times of that by uranium irradiation. |
| March 1941 | [U.S.A.] Improved measurement of cross section of uranium235by M.Tuve (the result was transmitted to England). |
| March 1941 | [England] Critical mass of uranium235 calculatedby R.Peierls. |
| April 1941 | [Japan] Army approves atomic bomb research. |
| 18.5.1941 | [U.S.A.] Cross section of new element 94239 assessed by E.Segre and G.Seaborg. Nuclear fission caused by slow neutron is 1.7times of that in uranium235. |
| May 1941 | [Japan] A lecture by Tokutaro Hagiwara of explosive uranium235. |
| 23.6.1941 | [England] George Paget Thomson and MAUD committee reports convincing evidence of developing uranium235bomb. |
| 11.7.1941 | [U.S.A.] A memorandum regarding a nuclear fission of the 94th element by E.Lawrence. (Possibility of plutonium bomb) |
| 24.7.1941 | [U.S.A.] The cross section of new element 94239. The nuclear fission caused by slow neutron is 3.4 times of that of uranium238. |
| September 1941 | [U.S.A.] Triggering by atomic bomb of hydrogen bomb studied by E. Fermi and E. Teller. |
| September 1941 | [U.S.A.] Construction of a graphite pile started by E. Fermiand L. Szilard. |
| 9.10.1941 | [U.S.A.] MAUD report brought to President Roosevelt by Vannevar Bush. Atomic bomb development project started with transferring the focus from nuclear reactor to atomic bomb. |
| October 1941 | Discussion by N. Bohr and W. Heisenberg of a heavy water type pile in Copenhagen. |
| 6.11.1941 | [U.S.A.] The 3rd NSA report of Compton committee. (Uranium bomb possible within 3-4 years. Fifty to one hundred million dollars for uranium enriching plant.) |
| November 1941 | [U.S.A.] Separation of uranium235 by J. Dunning and U. Booth. (A gas dispersion method using uranium fluoride (VI).) |
| 1.12.1941 | [U.S.A.] Data of nuclear fission of new element 94239 given to A. Compton by E. Lawrence. |
| 2.12.1941 | [U.S.A.] Separation of 100 micrograms uranium235by E. Lawrence. |
| 6.12.1941 | [U.S.A.] Submission of plutonium bomb project by A. Compton. |
| 8.12.1941 | [Japan] A surprise attack on Pearl Harbor. (In U.S.A. date was 7.12.1941) |
| 9.12.1941 | [U.S.A.] A plutonium bomb project started by A. Compton and V. Bush without report to President Roosevelt. |
| 16.12.1941 | [U.S.A.] V. Bush required participation of Engineering Brigade in atomic bomb project. |
| 18.12.1941 | [U.S.A.] OSRD creates the S-1 committee, a special committee created by V.Bush. [Connant, Briggs, Pegram, Compton, Lawrence, Urey, Samuel Allison, G. Bright, Edward Condon and Henry DeWolf Smyth] |
| 20.12.1941 | [U.S.A.] Budget for developing atomic bomb of $651,000 authorized. |
| December 1941 | [U.S.A.] Calutron built by E.O. Lawrence: A 184-inch cyclotron to separate U235. By the summer of 1942 most of the design problems had been solved. The new machine was named Calutron after the University of California. |