Table 1: A Brief Timeline of Nuclear Science Through World War II

Year Event or Discovery

1789Martin Klaproth, a German chemist, discovered uranium and named it after the planet Uranus.

1895

Wilhelm Conrad Rontgen discovered x-rays by passing an electric current through an evacuated glass tube. Doctors began using them to see inside the human body. Scientists began studying the effects of x-rays on various substances.

1896

In an effort to find x-rays in uranium, Antoine Henri Becquerel accidently discovered a new type of rays called ‘Becquerel rays’ in a uranium containing ore called pitchblende. The intensity of these rays was proportional to the amount of uranium. These rays later became known as beta rays/particles (electron emission) and alpha rays/particles (helium nuclei emission).

1896Paul Villard discovered gama-rays—similar to x-rays but more energetic—in the uranium containing ore pitchblende.

1896Pierre and Marie Curie gave the name ‘radioactivity’ to the phenomenon of ray/particle emission.

1898The Curies isolated polonium and radium from pitchblende. Radium was later used in medical treatments.

1898 Samuel Prescott showed that radiation destroyed bacteria in food.

1902Earnest Rutherford discovered that beta and alpha decay (particle emission) resulted in the formation of different elements.

1911Frederick Soddy discovered that naturally radioactive elements existed as different isotopes (same number of protons—different number of neutrons in nucleus) with the same chemical properties.

1911George de Hevesy showed that radionuclides (radioisotopes) were invaluable as tracers because small amount could be detected with simple instruments.

1919Ernest Rutherford fired alpha particles from radium into nitrogen causing nuclear rearrangement and the formation of oxygen.

1932James Chadwick discovered the neutron. Cockcroft and Walton caused nuclear transformations by bombarding atoms with high-speed protons.

1934Irene Curie and Frederic Joliot found that some nuclear transformations produced artificial radionuclides.

1935

Enrico Fermi discovered that using high-speed neutrons instead of protons could produce a much greater variety of artificial radionuclides, some being heavier and some being lighter.

Year Event or Discovery

1938

Otto Hahn and Fritz Strassman in Berlin showed that the new lighter elements were barium and others with about half the mass of uranium. This showed that atomic fission had occurred.Lise Meitner and Otto Frisch explained ‘neutron capture’ as the cause of nuclear fission and calculated the energy released from fission at 200 million electron volts.

1939

Otto Frisch experimentally confirmed the calculated the energy release from fission. This was the first experimental confirmation of Albert Einstein’s energy/mass relationship, E = mc2. Hahn and Strassman in Berlin, Joliot in Paris and Leo Szilard and Fermi in New York all confirmed the possibility of a self-sustaining nuclear chain (fission) reaction which could release tremendous amounts of energy according to E = mc2. The major obstacle was that natural uranium ores contained 0.7% U-235 and 99.3% U-238. The U-235 isotope was the much better candidate for producing fission reactions (as proposed by Neils Bohr). The final piece of the fission reaction puzzle was provided by Francis Perrin and Rudolf Peierls who introduced the concept of ‘critical mass’ which was the minimum amount of uranium needed to produce a self-sustaining fission reaction. Perrin also showed that using a neutron absorbing material to slow the chain reaction down could control the fission reaction. This is what makes nuclear power plants possible.

WWII USA Germany USSR

1939

President Roosevelt received a letter from Albert Einstein warning of the possibility of a uranium weapon.

Atomic fission research began with a nuclear reactor, ‘heavy water’ production and uranium enrichment.

Cyclotrons installed at the Radium Institute and Leningrad FTI.

1940

Neptunium and plutonium were produced using neutron bombardment of U-238 at the Berkeley cyclotron.

The world’s only ‘heavy water’ plant seized in Norway. First fission experiment failure.

Central Asian uranium deposits studied for use in nuclear energy research.

1941

Plutonium identified as a new fissionable element with atomic number 94. Manhattan project begun.

Graphite is rejected as a fission reaction moderator.

German invasion of Russia shifts emphasis of nuclear research to weapons development.

WWII USA Germany USSR

1942

Robert Oppenheimer became director of Manhattan project. First uranium isotope enrichment plant under construction in Oak Ridge, Tennessee. Enrico Fermi produced the first controlled and sustained fission reaction at the University of Chicago.

Emphasis of fission research shifted from military applications to energy production.

Joseph Stalin officially began a nuclear weapons development program.

1943

Planning for construction of breeder reactors for producing plutonium near Hanford, Washington began. Oppenheimer moved bomb development headquarters to Los Alamos, New Mexico

Fission research continued its decline due to politicization of the educational system and anti-Semitism, which was biased against theoretical physicists.

Soviet nuclear research focused on: achieving chain reactions; investigating methods of uranium enrichment; and designing both enriched uranium and plutonium bombs.

1944

First batch of spent fuel obtained from Hanford, Washington. The ALSOS mission acquired secret documents implying slowed Nazi research progress.

Experiments using graphite and heavy water as a fission reaction moderator were conducted.

1945

January - first plutonium reprocessing began at Hanford.January 20 - first U-235 separated at Oak Ridge, Tennessee.July 16 - first atomic explosion at Trinity site, near Alamogordo, New Mexico.

August 6 - Little Boy, a uranium bomb, was dropped on Hiroshima, Japan. Between 80,000 - 140,000 people were killed.August 9 - Fat Man, a plutonium bomb, was dropped on Nagasaki, Japan. About 74,000 people are killed.

Nazi Germany was defeated in May.

Following Nazi defeat in May, German scientists were ‘recruited’ to aid in Russian weapon development. After Hiroshima and Nagasaki were bombed, Russian weapons development went into high gear with plutonium breeder reactors becoming operational in the Ural mountains near Chelyabinsk. Also, the first gaseous diffusion uranium enrichment facility in Verkh-Neyvinsk was under construction.