hourglass

Timeline: Subatomic Concepts, Nuclear Science & Technology

Compiled by Sándor Nagy

Természettudományos Ismeretterjeszto Tartalmak

Linked pages (except for those of elements) will open in another window/tab. If a technical term is not clear, consult the following nuclear glossaries: ENS Glossary, IUPAC Glossary, Language of the Nucleus, Glossary of Nuclear Science Terms.

Links in the last column point to the relevant parts of The Nobel Prize site. The names of Nobel Prize winners are followed by the year of the award and the code of science (-c, -m, and -p for chemistry, medicine, and physics, respectively). Nobel Prize winners are only linked at the event most closely related to the achievement the prize was given for.
Links in the middle column point to sites where scientific terms etc. are illustrated or explained in more detail. Some links are coded as follows. @ - Animation, # - Chart, # - Data acquisition, & - Classic paper.
Technical notes: !!! broken link not yet fixed.

Year

Event - discovery, invention etc.

Worker(s)

1895

Discovery of X-rays @ @ as a result of fluorescence produced by cathode rays &. (Within a year the “American X-ray Journal” got published, showing the importance of the discovery in medicine @.) The name X-rays (X-Strahlen) was coined by Röntgen himself, although the same radiation is often referred to as Röntgen, Roentgen or Rontgen radiation.

Röntgen W.C. (1901-p)

1896

Discovery of radioactivity, i.e., natural uranium (92U) emits penetrating radiation similar to that discovered by Röntgen. Becquerel found that the radiation from potassium uranyl sulfate, K2UO2(SO4)2.2H2O, blackens “Lumiere photographic plate # with a bromide emulsion in two sheets of very thick black paper”, causes scintillations on a fluorescent screen, and discharges electroscopes &.

Becquerel A.H. (1903-p)

1896-1898

Examining a large number of minerals by electroscope to find radioactivity in them. The Curies found that thorium (90Th) is just as active as uranium. They introduced the term radioactive to denote substances that emit “Becquerel's radiation”. They noticed that a material is the more radioactive, the more uranium and/or thorium it contains @. They also found that pitchblende is more radioactive than it would follow from its U and Th content, giving the first hint to the possible existence of other radioactive elements &.

Curie M.
Curie P. (1903-p)

1897

Discovery of the electron, the first of the subatomic particles. Its identification as the particle constituting cathode rays @. Thomson also determined the charge to mass ratio (e/me) of the electron &. He found that electrons are tiny negative particles.

Thomson J.J. (1906-p)

1898

Discovery and chemical study of polonium (84Po) & and radium (88Ra) &. Radiochemistry (RC) is born. (Note that 1000 kg of uranium ore contains only 100 μg of Po and 140 mg of Ra.)

Curie M. (1911-c)
Curie P.
Bémont M.G.

1898-1899

Recognition that the radiation of uranium contains (at least) two components. The one (α radiation as Rutherford named it) is “very readily absorbed”, the other (β radiation) is “of a more penetrative character” &. They were diverted by a magnetic field # in opposite directions, showing that α particles # are positive and β particles # are negative.

Rutherford E.

1898-1902

Discovering that radiations have chemical and biological effects. In spite of the early warnings, shoe fitting fluouroscopes working with X-rays were still in use in the US as late as in the 1940s.

Becquerel A.H.
Bloch E.
Curie M. ...

1899

Discovery of actinium (89Ac), some isotopes of which are members of two naturally occurring decay series #. The longest-lived isotope of this unstable element is 227Ac (T1/2 = 21.77 a).

Debierne A.-L.

1899-1900

Discovery of radon (86Rn), a noble gas, some isotopes of which are members of the naturally occurring radioactive decay series. The longest-lived isotope of this unstable element is 222Rn (T1/2 = 3.8 d), member of the 4n+2 (238U) series.

Curie M.
Curie P.
Dorn F.E.
Rutherford E.

1900

Proving that β-rays are electrons @ (just like cathode rays).

Becquerel A.H.

1900

Discovery of γ-rays, the type of (neutral) radiation that does not bend in a magnetic field #. He also found that the radiation (named by Rutherford 3 years later) has even larger penetration depth than X-rays and other radiations connected with radioactivity #.

Villard P.

1901

Postulating that electromagnetic energy can only be emitted in quanta, and the elementary energy unit is E = , where h is Planck's constant and ν is the frequency of the radiation.

Planck M.K.E.L. (1918-p)

1902

First macroscopic amounts of a radioelement (radium) are separated #. A big step in RC with practical relevance to the development of radium therapy. M. Curie isolated by that time 120 mg of RaCl2 from about 2000 kg of pitchblende. She also determined the atomic weight of Ra (225) and identified it as the heaviest alkaline earth.

Curie M.
Curie P.
Debierne A.-L.

1902

Discovery of the exponential law of radioactive decay @ while studying 220Rn (thorium emanation, thoron, T1/2 = 55 s), member of the 4n (232Th) series &. Rutherford also introduced the technical terms half-life (T1/2) and radioactive constant (λ) now called decay constant # or disintegration constant.

Rutherford E.
Soddy E.

1903

“observation that the spectral lines of helium appear in the emanations from radium &, that very puzzling element, an observation which may bear fruit in results for science, the full extent of which it is now impossible to foresee” - cited from the Presentation Speech in honor of W. Ramsay (1904-c). A valuable hint for the identification of α-particles as 4He2+ ions in 1909.

Ramsay W.
Soddy E.

1903

Realizing that atoms are not unchangeable, i.e. radioactive decay is the spontaneous transformation of one element into another @ accompanied by the emission of a radiation particle. (Although vaguely phrased, this idea already appeared at the end of their paper published in 1902 &.) The genetically related atomic species (parentdaughter) can form whole series of transformations, i.e. radioactive decay series @.

Rutherford E. (1908-c)
Soddy F.

1903-1906

Proposing the plum-pudding model # of the atom, according to which the atom is to be pictured as a positively charged massive sphere, whose charge is neutralized by an appropriate number of tiny electrons embedded in it. Thomson estimated the number of electrons to be roughly equal to the atomic number Z.

Lord Kelvin (Thomson W.)
Thomson J.J.

1904

Proving that the penetration depth called range of α-rays is very short #.

Bragg W.H.

1904-1906

Proving that cancer cells are more sensitive to X-rays than healthy ones. (In the same period it was also found that radium rays are useful for treating tumors of the skin and the cervix.)

Bergonié J.
Tribondeau L.

1905

Giving statistical interpretation of the decay constant λ and the exponential law discovered by Rutherford and Soddy by assuming that the probability p for a single atom to decay in a very short time interval Δt is given by the equation p = λ Δt.

Schweidler E.

1905

The equivalence of rest energy and mass is recognized (E0 = mc2). However, Einstein won his Nobel Prize for the explanation of the photoelectric effect (PE) (discovered by Ph. Lenard in 1902, explained by Einstein in 1905). In order to do this, he interpreted Planck's energy quanta as photons (light quanta) of energy E = . (PE is one of the major interactions of high-energy photons @ such as X-rays and γ-rays with matter especially in the case of high-Z elements.)

Einstein A. (1921-p)

1906

Recognizing the potential of radioactivity as a geological clock @. Proposing that the amount of helium accumulated in uranium-bearing rocks could be used as a measure of the time elapsed since crystallization.

Rutherford E.

1906

Discovery of weak β radioactivity of alkali metals including potassium thus proving that radioactivity is not restricted to heavy elements. 40K as the cause of potassium activity was only identified in 1935 (A.O. Nier).

Campbell N.R.
Wood A.

1908

Determination of Avogadro`s constant, thus making possible to determine atomic mass from gram atomic mass used by chemists.

Perrin J.

1909

Proving that α-rays are ionized helium atoms @ # whose “charge is twice the unit charge carried by the hydrogen atom set free in the electrolysis of water”. In other words, α ≡ 4He2+ &.

Rutherford E.
Royds T.

1909-1910

Showing that a small fraction of α particles incident on a thin gold foil scatter at large angles @ & &, a contradiction with the “plum pudding” model of the atom. In 1913 Geiger and Marsden experimentally checked Rutherford`s nuclear atom theory (1911) inspired by their early experiments &.

Geiger H.
Marsden E.

1910

Measurement of the electron`s charge (-e) #. From this and from Thomson`s 1897 result on the charge to mass ratio of the electron Millikan was also able to determine the electron`s mass (me), which turned out very tiny (0.054% of that of a H atom).

Millikan R.A. (1923-p)

1910

Analytical solution for the differential equation system describing the kinetics of decay series in the general case (Bateman equations).

Bateman H.

1911

Determining the number of electrons per atom by X-ray scattering. Thomson`s 1906 guess turned out correct: the number of electrons is given by the atomic number Z. (Later, in 1917, Barkla won the physics Nobel Prize for the discovery of “characteristic Röntgen radiation”.)

Barkla C.G.

1911

Proposing the existence of a tiny but massive atomic nucleus & & to explain the results of the α-scattering experiments @ @ performed by Geiger and Marsden. The positive charge of the nucleus equals that of the negative charge of electrons that swarm around it @, making the atom neutral as a whole. Considering Barkla`s result obtained same year it also means that the nuclear charge is eZ.

Rutherford E.

1911

Discovery of the Geiger-Nuttall rule, an empirical linear relationship between the logarithms of the decay constant of naturally occurring α emitters and the range of the α particles in air. The relationship was immediately interpreted in terms of half-life and α-energy #, showing that a little increase in energy is related to an enormous decrease in half-life amounting to several orders of magnitude. The explanation followed in 1928 with the quantum theory of α decay (E.U. Condon, G. Gamow, R.W. Gurney).

Geiger H.
Nuttall J.M.

1912

Inventing the expansion cloud chamber @ (Wilson chamber) that makes the individual tracks of ionizing particles (e.g., α- and β-rays) visible by condensation of vapor.

Wilson C.T.R. (1927-p)

1912

Discovering cosmic radiation higher in the atmosphere using balloon flights. [Hess made use of the fact that the intensity of cosmic rays is quite large at high altitudes compared with other sources of radiations @.]

Hess V.F. (1936-p)

1913

Postulating the existence of “non-separable elements of different atomic weight” to explain the “chemical non-separability” of some radioactive species having different decay properties &. Later that year Soddy names them “'isotopes' or 'isotopic elements', because they occupy the same place in the periodic table” &. This recognition was in great part due to A. van den Broek's idea, namely, that the place of the element on the periodic table is determined by the “intra-atomic charge” (i.e. Z) and not by the "atomic weight" (i.e. A) &. Proof for the existence of isotopes in general # as atomic species of different atomic mass was given by Thomson same year through deflecting neon ions in electromagnetic fields and concluding, “neon is not a simple gas but a mixture of two gases, one of which has an atomic weight about 20 and the other about 22”. The first isotope separation of neon was performed in Thomson's lab by Aston through gas diffusion before WWI &. By now lots of separation techniques # # have been developed.

Fajans K.
Soddy F. (1921-c)

Thomson J.J.
Aston F.W.

1913

First application of radioactive tracer technique to measure the solubility of PbCrO4 using 212Pb (then named ThB, T1/2 = 10.64 h), a member of the thorium 4n decay series. Hevesy made use of the "chemical non-separability" of some radioactive species which later came to be known as (radio)isotopes of the same element.

Hevesy G. (1943-c)
Paneth F.A.

1913

Recognition of the displacement laws, i.e. that the product of α decay @ @ is the element two columns to the left from the parent element in the periodic table, whereas the product of β decay @ (actually β- decay) is one column to the right &. Later on the term β decay got generalized to include electron capture @ (EC) and β+ decay as well, for which the change is one column to the left in the periodic table, i.e., one step towards “south-east” direction in the nuclide chart @.

Fajans K.
Soddy F.

1913

Discovery of protactinium (91Pa), a member of two naturally occurring decay series. It is also the second member of actinides enclosed by 90Th and 92U. Its first isotope found, 234Pa (T1/2 = 6.7 h), is member of the 4n+2 (238U) series. The longest-lived isotope of this unstable element is 231Pa (T1/2 = 32.5 ka).

Fajans K.
Göhring O.H.

1913

Creation of the second best pre-wave mechanical atomic model by Bohr @ @ @ @ using Rutherford's nucleus concept as well as some ideas from A. Einstein and M. Planck & &. It was also clear to Bohr that radiation particles including β particles originate from the decaying nucleus. Bohr's model was further developed by A.J.W. Sommerfeld in 1916 (the Bohr-Sommerfeld model).

Bohr N.H.D. (1922-p)

1913

First study on the intravenous injection of radium for therapy. It happens that this same year the Coolidge (hot-cathode) X-ray tube @ was invented revolutionizing the field of radiology. (Next year: a monthly periodical – the American Journal of Roentgenology and Radium Therapy – was first published showing that radiotherapy reached a “critical mass” by that time.)

Proescher F.

1913-1914

Discovering the relationship between the atomic number Z and the (characteristic) X-ray spectrum of the elements. The elements get their final place in the periodic table from H to U. Elements yet to be discovered can be specified by their atomic numbers &.

Moseley H.G.

1914

Proving the assumption of A.H. Becquerel and P. Villard, namely, that γ-radiation is of electromagnetic nature (just like X-rays, bremsstrahlung @, UV, IR, microwaves, radio waves and visible light). Using modern terminology, we would say:γ-rays are photons @.

Andrade A.N.
Rutherford E.

1919

Producing the first nuclear reaction @, 4He + 14 17O + 1H, using natural α-radiation &. Rutherford is also credited with the discovery of the proton (the positive type of nucleon) by identifying the nucleus of the lightest atomic species 1H formed in the above reaction as a building unit of atomic nuclei. Actually what he wrote was: “the hydrogen atom which is liberated formed a constituent part of the nitrogen nucleus”.

Rutherford E.

1919

Inventing the first mass spectrometer @ originally called "positive-ray spectrograph". Aston used it for discovering various isotopes in non-radioactive elements. & &

Aston F.W. (1922-c)

1921

Observing that 234Pa (a β decaying nuclide of the 4n+2 series) consists of two radioactive components with different half-lives (1.17 min and 6.7 h). Hahn's observation was later acknowledged as the discovery of nuclear isomerism, i.e. of the existence of relatively long-lived excited (metastable) nuclei (234mPa in this case) whose decay properties are different from those of the ground-state nucleus. (They often decay to the ground state by γ-emission.)

Hahn O.

1923

Discovery of the Compton effect, the quasi-elastic scattering of γ-photons on (valence) electrons @ &. (See for Compton's other papers here: &.)

Compton A.H. (1927-p)

1924

Hypothesizing that all particles have wave properties @ @. De Broglie proposed a relationship between the speed u of a particle of mass m and its wavelength: λdB = h/(mu), where h is Planck's constant. The formula is more generally written in the form λdB = h/p, where p is the (relativistic) momentum of the particle and λdB is its de Broglie wavelength.

de Broglie L.P.R. (1929-p)

1924-1926

Developing the coincidence method that was first tried out for the Compton effect. Simultaneously measuring the momentum and energy for the scattered photon and electron from the same Compton event, they concluded that Bohr, Kramers, and Slater were wrong when they assumed in 1924 that the conservation laws are only valid statistically but not for individual events.

Bothe W. (1954-p)
Geiger H.

1924-1927

The quantum mechanical model of the atom is developed together with the Pauli exclusion principle and the Heisenberg uncertainty relationship #. The theory was inspired by de Broglie's hypothesis of the wave-particle duality of matter.

Heisenberg W.K. (1932-p)
Dirac P.A.M.
Schrödinger E.R. (1933-p)
Pauli W.E. (1945-p)

1925

Inventing the first linear accelerator @ (linac). (This achievement is often attributed to R. Wideröe, who published his paper on accelerating sodium and potassium ions in 1928.)

Ising G.

1926

Discovery of the spin (the intrinsic angular momentum) of the electron (1/2 ħ). They assumed that the magnetic momentum associated with spin is larger by a factor of 2 than that related to orbital angular momentum of the same magnitude. L.H. Thomas concluded from relativity theory that the assumption was correct.

Goudsmit S.A.
Uhlenbeck G.E.

1927

Showing that (similarly to X-rays) electrons are diffracted by crystals, thus proving de Broglie's hypothesis and founding electron diffraction methods as well as electron microscopy #.

Davisson C.J.
Thomson G.P. (1937-p)
Germer L.H.

1927

Proving on banana flies that irradiation with X-rays causes mutations in them. Muller is considered the father of radiation genetics.

Muller H.J. (1946-m)

1927

Explanation of the conservation of parity in atomic transitions as a result of reflection invariance, or right-left symmetry, of the electromagnetic forces in the atom. Note that Wigner's Nobel Prize came after C.S. Wu et al. proved in 1957 the violation of this particular symmetry called P symmetry. (The Noble Prize was given “for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles”.)

Wigner E.P. (1963-p)

1927

Patent for a pump for liquid metals. Its inventors cannot have foreseen that, but similar pumps containing no moving parts circulate liquid sodium coolant in some nuclear reactors today. This was just one example of Szilard's inventiveness. (Leo Szilard = Szilárd Leó in Hungarian.)

Einstein A.
Szilard L.

1928

Developing the quantum mechanical theory of α decay. The theory explains how the α particles pre-formed in the decaying nucleus can get through a potential wall of finite thickness (Coulomb barrier #) that is higher than the energy they possess. The phenomenon is referred to as tunneling #.

Condon E.U.
Gamow G.
Gurney R.W.

1928

Constructing the first detector counting individual particles (GM-counter, GM-tube). This type of gas-filled detector # @ is not suitable for energy measurements.

Geiger H.
Müller J.W.

1930

Postulating the neutrino @ to explain the continuous energy spectrum of β decay # that seemed to contradict energy conservation. The neutrino taking away the missing energy was only found a quarter of a century later in 1956. (It was originally named neutron by Pauli, but it was soon renamed by Fermi.)

Pauli W.E.

1931

Constructing an electrostatic generator (van de Graaff generator #) consisting of a large hollow spherical electrode and a rapidly moving belt &. It can accelerate charged particles to 10 MeV.

van de Graaff R.J.

1932

Developing a high-voltage machine (Cockcroft-Walton voltage multiplier #) based on charge capacitors that discharge and drive charged particles through an accelerating tube. They were the first to use accelerated particles for the transmutation of nuclei.

Cockcroft J.D.
Walton E.T.S. (1951-p)

1932

Building the first cyclic resonance accelerator (cyclotron) @ &. Lawrence tried out his idea from 1930 already in 1931.

Lawrence E.O. (1939-p)
Livingston M.S.

1932

Discovering deuterium 2H, the heavy isotope of hydrogen. Urey et al. enriched deuterium by evaporating liquid hydrogen && &. The name given by the discoverer divided scientists. Rutherford's followers referred to it as “diplogen” for years.

Urey H.C. (1934-c)
Brickwedde F.G.
Murphy G.M.

1932

Discovery of the neutron, the second (electrically neutral) type of nucleon &. Thus the main building blocks and the basic structure of the nucleus have been discovered. (In his Bakerian lecture in 1920 &, Chadwick's teacher, Rutherford, mentioned a “kind of neutral doublet” – a tiny hydrogen atom – as part of the nucleus to explain the discrepancy between Z and the atomic weight.) The neutron – in its free state – is unstable. It beta-decays to proton # with a half-life of 10.6 min.

Chadwick J. (1935-p)

1932

Discovery of the positron e+ - the antiparticle of the electron e (or negatron e-) - by studying cosmic rays in a cloud chamber &. Positrons are stable, but encountering with electrons, the pair annihilate, most often by 2γ annihilation @. β+-particles are also positrons. (The existence of the antiparticle of the electron was theoretically deduced by P.A.M. Dirac in 1930.)

Anderson C.D. (1936-p)

1932

Developing a counter-controlled cloud chamber to increase the efficiency of the observation of cosmic radiation from about 5% to 80%. “Triggering” was done by two GM-counters (one above the chamber, another underneath) working in coincidence. In 1933, Blackett et al. also observed pair production @ # (i.e. the process γ  e+ + e-, the opposite of annihilation) with high-energy photons of cosmic origin. (Nobel lecture)

Blackett P.M.S. (1948-p)
Occhialini G.

1933

Discovering isotope effects in chemical reactions.

Rittenberg D.
Urey H.C.

1933

Deducing from experiments that the attractive force between two nucleons has a very short range, i.e. it is very weak except when the nucleons are very close together. Within that range, however, it is a very strong force, in fact, many times stronger than the long-range electric forces at the same distance. Nowadays this force is alternatively called nuclear force or residual strong force # #.

Wigner E.P.

1933

Discovering by the molecular ray method that the proton's magnetic moment is about 2.5 times larger than expected from contemporary theory. I.I. Rabi (1944-p), using his 1% accuracy resonance method, confirmed the anomalous magnetic moment of the proton. [The electron's magnetic moment measured by P. Kusch (1955-p) was only 0.119% higher than expected.]

Stern O. (1943-p)

1934

Observation of the "transmutation effects" (fusion @)of "diplogen" (deuterium) nuclei &. The reactions were thought to be 2H + 2H → 3H + 1H and 2H + 2H → 3He + 1n, i.e. 2H(d,p)3H and 2H(d,n)3He, where d ≡ 2H+ "diplon" (now called deuteron).

Oliphant M.L.
Harteck P.
Rutherford E.

1934

Patent for the idea of a nuclear chain reaction @.

Szilard L.

1934

Discovering artificial radioactivity: 4He + 27Al  30P + n; 30 30Si + β+ (T1/2 = 2.5 min). The Joliot-Curie couple managed to publish the discovery before M. Curie, I. Joliot-Curie's mother, died in 1934. The timing is also of relevace to H.G. Wells as a Sci Fi author and his scientific extrapolations written in his book 'The World Set Free'.

Joliot F.
Joliot-Curie I. (1935-c)

1934

Working out the theory of β-decay @ # by fusing radiation theory with W.E. Pauli's idea (from 1930) of the neutrino (which he thought mass-less, mν = 0, like photons). Fermi showed (together with E. Amaldi, O. D'Agostini et al.) that neutrons react with most nuclei (neutron capture @) and also proved (together with F. Rasetti) that neutrons slowed in water or paraffin (by collision with protons) are much more reactive.

Fermi E. (1938-p)

1934

Discovering the Szilard-Chalmers process meaning that recoil energy in neutron capture may cause the daughter nuclide to break free from the chemical bond. This observation opened the way to hot-atom chemistry and labeling methods.

Szilard L.
Chalmers T.A.

1934-1937

Discovery and interpretation of the Cherenkov radiation - light emission along the track of particles whose speed in the given substance exceeds the speed of light in that same substance.

Cherenkov P.A.
Frank I.M.
Tamm I.Y. (1958-p)

1935

Discovering the Oppenheimer-Phillips process, a special type of stripping reaction or particle transfer @, in which the nucleus absorbs the neutron of a passing deuteron even though the energy of the latter is not enough to overcome the Coulomb barrier. The proton thus escapes being absorbed, e.g.: 12C(d,p)13C. The process is supposed to explain why (d,p) reactions are more at low energies than (d,n) reactions. Sixty years later this effect was declared as non-existent by Gy. Bencze and C. Chandler.

Oppenheimer J.R.
Phillips M.

1935

Predicting the existence of massive (200 me) particles called mesons which would mediate the short-range nuclear forces between nucleons just as photons (mγ = 0) mediate long-range electromagnetic forces between charged particles. (The heavier the "messenger", the shorter the range of the force.)

Yukawa H. (1949-p)

1935

Deriving a formula for the mass/binding energy of the nucleus @ # (Weizsäcker formula, the original form of what is known as the semi-empirical mass formula). The derivation is based on the assumed similarity between the nucleus and a drop of liquid. (Note that the liquid drop model itself was only developed in 1937, but the analogy between the atomic nucleus and a drop of liquid was first suggested by G. Gamow in 1929.)

Weizsäcker C.F.

1936

Inventing the diffusion cloud chamber working with dry ice and ethanol. Due to a vertical temperature gradient in the vapor layer, the tracks of ionizing particles are automatically washed away in a short time, so there is no need for periodic compression-decompression cycles as opposed to the Wilson chamber.

Langsdorf A.

1936

Inventing neutron activation analysis based on the determination of the half-lives of the radionuclides # # # (then called radioactive isotopes or radioisotopes) produced in the sample rather than on the characteristic energies of the γ-photons emitted the way it is done today.

Hevesy G.
Levi H.

1936

Creation of the compound-nucleus model of nuclear reactions involving the amalgamation of the colliding nuclei. The excess energy leads eventually to the 'evaporation' of a nuclear particle which leaves the compound nucleus at random direction.

Bohr N.

1937

Developing the liquid drop model of the nucleus (the first one of the nuclear models), which came in very useful two years later (N. Bohr and J.A. Wheeler) for the explanation & of induced fission @ discovered in 1939.

Bohr N.
Kalckar F.

1937

Isolation of the first artificial element technetium (43Tc) produced by bombarding molybdenum atoms with deuterons accelerated in a cyclotron. The box between 42Mo and 44Ru, "reserved" for Tc in the periodic table, had been empty until then, because its most stable isotope, 98Tc, had become extinct billions of years ago due to its "short" half-life (T1/2 ≈ 4.2 Ma). (The discovery of Tc - then named "masurium" - may be 12 years older though. In 1925, W. Noddack, I. Tacke and O. Berg reported on its discovery from X-ray spectra, but they were discredited. J.T. Armstrong of NIST, on account of X-ray spectra simulated in 1999, thinks Noddack actually found 99Tc, a spontaneous fission product of 238U.)

Perrier C.
Segrè E.G.

1937

Discovery of electron capture (EC) @, an alternative process competing with β+ decay.

Alvarez L.W.

1937

Discovery of the muon (μ) in cosmic radiation. The muon was originally called μ-meson in the belief that it was the meson predicted by H. Yukawa. However, it turned out to be "just" a heavier relative of the electron (mμ ≈ 207 me), which is a lepton #.

Anderson C.D.
Neddermeyer S.H.

1937

Suggesting the β- decay of 40K to 40Ar to be used as a geochronological clock for dating potassium-bearing minerals @ .

Weizsäcker C.F.

1938

Theory for energy production in stars through fusion of 1H nuclei to 4He via the carbon-nitrogen (CNO) cycle @. (The PP chain # energizing the Sun produces helium without carbon as a 'catalyst'. The net reaction is called "hydrogen burning"@. Stars heavier than the Sun, on the other hand, can even "burn" helium via a series of reactions introduced by the rare triple alpha process @. The simple 2α process does not work because of the extremely short half-life of 8Be that is formed.)

Bethe H.A. (1967-p)

1939

Discovery of induced fission @ # of uranium irradiated with neutrons &. Hahn et al. were hoping that uranium would transform to a heavier (transuranium) element, but they found it to split to two smaller parts called fission fragments @.
Meitner immediately realized the hugeness of the energy released in fission (~200 MeV)
&. She also soon became aware of the possibility of chain reaction @ # maintained by neutrons.

Hahn O. (1944-c)
Strassman F.
Meitner L.
Frisch O.R.

1939

Discovery of francium (87Fr) in the 4n+3 (235U) decay series as the α-decay product of 227Ac. Ms. Perey obtained the longest-lived isotope 223Fr (T1/2 = 22 min) named "actinium-K" (AcK).

Perey M.

1939

Discovery of β-delayed neutron emission @ (βn) in fission products.

Roberts R.B
Hafstad L.R.
Meyer R.C.
Wang P.

1939

Determination of the magnetic moment of neutron to 1% accuracy by Bloch and Alvarez at the Berkeley cyclotron.

Alvarez R.W.
Bloch F.

1940

Discovery of astatine (85At), some isotopes of which are members of the naturally occurring decay series. It had been synthesized at the University of California, Berkeley, in the reaction 209Bi(4He,2n)211At (T1/2 = 7.21 h). The longest-lived isotope of this unstable element is 210At (T1/2 = 8.1 h).

Corson D.R.
Mackenzie K.R.
Segrè E.G.

1940

Discovery of the spontaneous fission @ (SF) of 238U, a decay mode found later in other heavy nuclides as well, indicating that the periodic table must have an upper limit for Z somewhere.

Flerov G.N.
Petrzhak K.A.

1940

Production of the first transuranium element neptunium (93Np). Neptunium directly follows uranium (92U), the heaviest naturally occurring (however unstable) element, which is abundant enough to be produced by mining etc. McMillan and Abelson obtained 239Np (T1/2 ≈ 2.4 d) by bombarding uranium with slow neutrons. Its most stable isotope, 237Np, has a half-life of 2.144 Ma.

McMillan E.M. (1951-c)
Abelson P.H.

1941

Production of the second transuranium element plutonium (94Pu) by bombarding 238U with deuterons accelerated in a cyclotron. Seaborg et al. obtained 238Pu (T1/2 ≈ 87.7 a). The discovery was only disclosed after WW2 (1946, Kennedy et al.). In the meantime it was also discovered that 239Pu (T1/2 ≈ 24.1 ka) is fissile (i.e. neutrons can split it). The most stable plutonium isotope, 244Pu, has a half-life of 80 Ma.

Kennedy J.W.
Seaborg G.T.
Segrè E.G.
Wahl A.C.

1942

Building the first nuclear reactor (CP-1) # # &. Fermi was later inducted into the National Inventors Hall of Fame as "one of the most important architects of the nuclear age".

Fermi E. et al.

1943

Creating quantum electrodynamics, a theory used with great success in the study of particles and their transformations (e.g. Feynman diagrams).

Feynman R.P.
Schwinger J.
Tomonaga S-I. (1965-p)

1944

Formulation of the actinide concept of heavy-element electronic structure, i.e. 15 actinides (most of which were still undiscovered) would form a series analogous to the rare-earth series of lanthanides. Np and Pu, the first transuranium elements discovered before, were also the two first artificially produced elements on Earth to fill the 11 empty boxes after U "reserved" for actinides in Seaborg's new periodic system.

Seaborg G.T. (1951-c)

1944

First production of the actinide americium (95Am) by exposing 239Pu to neutrons in a nuclear reactor. Seaborg et al. obtained 241Am (T1/2 ≈ 432 a). The discovery was only disclosed after WW2 in 1949, by which time the same nuclide had also been synthesized by the process 238U(α,n)241Pu→241Am. The most stable isotope of americium, 243Am, has a half-life of 7.37 ka.

Seaborg G.T.
James R.A
Morgan L.O.

1944

First production of the actinide curium (96Cm) by bombarding 239Pu with cyclotron-accelerated 4He ions (α-particles). Seaborg et al. obtained 242Cm (T1/2 ≈ 163 d). The discovery was only disclosed after WW2 in 1949. The most stable curium isotope is 247Cm (T1/2 ≈ 15.6 Ma).

Seaborg G.T.
James R.A
Ghiorso A.

1944

Discovery of synchrotron principle making possible that ions accelerated in a cyclic resonance accelerator remain on the same circular track #. (In the cyclotron they spiral out as they gain kinetic energy.) Energies higher than 1 GeV can be reached.

McMillan E.M.
Veksler V.I.

1945

Production of the first fission bombs (Manhattan Project). A 13 kt TNT-equivalent (55 TJ) U-235 bomb (Little Boy #) was dropped on Hiroshima and a 25 kt (105 TJ) Pu-type bomb (Fat Man - containing mostly Pu-239) over Nagasaki the same year.

Oppenheimer J.R.

1945

Promethium (61Pm) was first synthesized as fission product from thermal-neutron fission of 235U at the Clinton Lab (Oak Ridge National Laboratory) using chemical separation by ion exchange chromatography. The discovery was only disclosed in 1947. The fission products 147Pm and 149Pm were also produced by neutron activation of neodymium. The longest-lived isotope of this unstable element is 145Pm (T1/2 = 17.7 a).

Marinsky J.A.
Glendenin L.E.
Coryell C.D.

1946

Disclosing that (contrary to the expectations based on the liquid drop model) 235U @ # and 239Pu fission asymmetrically (producing two main 'chunks' of about A = 100 and 130, respectively, as well as a number of neutrons).

Siegel J.M. et al.

1946

Developing the radiocarbon (14C) @ method of radiometric dating #. Libby's method has been used in archaeology, geology, geophysics, and other branches of science.

Libby W.F. (1960-c)

1946

Discovery of nuclear magnetic resonance (NMR), a phenomenon serving as a basis for NMR spectroscopy as well as MRI # # (magnetic resonance imaging). The discoverers observed that nuclei possessing intrinsic magnetic moment (mostly odd-A nuclei), like 1H, 13C and 31P, can absorb RF energy when placed in a magnetic field of appropriate strength. The "resonance" depends on the chemical environment of the given nuclide. The strength of the NMR method is proven by two Nobel Prizes in chemistry, one for R.R. Ernst (1991-c) and another for K. Wüthrich (2002-c). The other branch of applications, MRI, also resulted in a shared prize in medicine for P.C. Lauterbur and P. Mansfield (2003-m).

Bloch F.
Purcell E.M. (1952-p)

1946

Publication of the first table of atomic species using Z vs. N presentation, which we would call today a chart of nuclides #.

Friedlander G.
Perlman M.

1946-1950

Establishing the bases of neutron diffraction measurements as a method of structure determination like X-ray diffraction.

Shull C.G. (1994-p)
Wollan E.

1947

Discovery of charged pions+, π-), the mesons predicted by H. Yukawa in 1935 as mediators of the short-range attractive force (nuclear force) between nucleons. The π-mesons (mp ≈ 273 me) were detected in the cosmic radiation using photo-emulsion. (In 1948, pions as well as muons were artificially produced in Lawrence's lab.)

Lattes C.M.G.
Muirhead H.
Occhialini G.P.S.
Powell C.F. (1950-p)

1947

Advancing the term nuclide to denote a species of atoms characterized by the same combination of atomic number Z and mass number A. (Hence, the different isotopes of an element form a special group of nuclides having the same Z but different A.)

Kohman T.P.

1947

Inventing the scintillation detector #, a combination of a scintillator (see A.H. Becquerel's 1896 discovery) and a photoelectron multiplier. Such a detector can be used not only for counting particles/photons but also measuring their energy.

Broser V.I.
Coltman J.W.
Kallman H.
Marshall F.H.

1947

Creating a two-step model for nuclear reactions induced by high-energy projectiles. In the first stage the projectile passes its energy to a number of nucleons starting an intranuclear cascade. As a result some of them leave the nucleus. The second (longer) stage involves the evaporation of spallation products from the highly excited nucleus.

Serber R.

1949

Establishing the (single-particle) shell model of the atomic nucleus that explains nuclear magic numbers in terms of increased stability due to closed shells. The model builds upon a strong coupling between the spin and orbital angular momentum of the nucleon. (M.G. Mayer is for Maria Göppert-Mayer), one of the few ladies among the Nobel Laureates.)

Haxel O.
Jensen J.H.D.
Mayer M.G. (1963-p)
Suess H.E.

1949

First production of the actinide berkelium (97Bk) by bombarding 241Am with cyclotron-accelerated 4He ions (α-particles). Thompson et al. obtained 243Bk (T1/2 ≈ 4.5 h.). The most stable berkelium isotope, 247Bk, has a half-life of 1400 a.

Thompson S.G.
Ghiorso A.
Seaborg G.T.

1949

Inventing the semiconductor detector (a Ge counter) whose descendants are powerful tools in γ-spectroscopy and NAA.

McKay K.G.

1949

The chemical environment was found to affect the electron-capture decay constant of 7Be (decaying only by EC). The variation was about 0.1%. (In 1970 H.W. Johlige et al. found that λEC was proportional to the electron density in the nucleus. In 2004, T. Ohtsuki et al. found about 0.8% difference in electron-capture half-life between 7Be@C60 and 7Be in metallic form.)

Leininger R.F.
Segrè E.
Wiegand C.

1950

Beta-delayed alpha decay @ was observed in 8B that beta-decays to short-lived 8Be splitting apart to two α particles. (The instability of 8Be explains that "helium burning" in massive stars can only start with the rare "three alpha process"@ directly producing 12C, rather than the more common and "logical" "two alpha process" leading to 8Be.)

Alvarez L.W.

1950

Discovery of neutral pion π0 at the Berkeley cyclotron. Steinberger et al. identified it by its decay into two photons @. This was the first discovery of a subatomic particle using accelerator.

Panofsky W.
Steinberger J.
Steller J.

1950

First production of the actinide californium (98Cf) by bombarding 242Cm with cyclotron-accelerated 4He ions (α-particles). Thompson et al. obtained 245Cf (T1/2 ≈ 45 min). The most stable californium isotope, 251Cf, has a half-life of 900 a. 252Cf is one of the heavy nuclides undergoing spontaneous fission @ (SF).

Thompson S.G.
Street Jr. K.
Ghiorso A.
Seaborg G.T.

1951

The first breeder reactor started its 12 years of operation to produce the world's first usable amount of electricity (enough to operate 4 light bulbs #) from nuclear power. EBR-I @ is now a Registered National Historic Landmark of the USA (dedicated so in 1966 by President L.B. Johnson and G.T. Seaborg, then chairman of the AEC).

 

1951

Discovery of positronium # (Ps), an atom-like bound state of a negatron e- and its antiparticle, the positron e+. Positronium can only form after the positron gets thermalized @ (i.e. slows down to thermal energies). Positronium has become the target of positronium chemistry and a probe in certain types of chemical (e.g. surface chemical) studies.

Deutsch M.

1952

Inventing the bubble chamber that is based on the same principles as the Wilson chamber (vapor-liquid phase transition, compression-decompression) but the tracks of ionizing particles appear in the liquid as bubbles rather than droplets in a vapor. Since particles have shorter range in condensed phase (like liquid diethyl ether in this case), it is more suitable for making the tracks of high-energy particles visible than the cloud chambers.

Glaser D.A. (1960-p)

1952

The first fusion device was produced and detonated. The explosive effect of "Ivy Mike"@ matched that of 10.4 Mt of TNT, i.e. it was 400 times more powerful than the fission bomb "Fat Man". "Ivy Mike" is also referred to as the first hydrogen bomb although it was too big for a practical weapon.

Teller E.
Ulam S.

1952-1953

Discovery of the actinides einsteinium (99Es) and fermium (100Fm) in the radioactive debris of the first fusion device by three teams from the Berkeley Radiation Laboratory (BRL), from the Argonne National Laboratory (ANL) and from the Los Alamos Scientific Laboratory (LASL). The nuclides 253Es (T1/2 ≈ 20.5 d.) and 255Fm (T1/2 ≈ 20 h.) were formed from 238U by a series of neutron captures (resembling the r-process in supernovae) followed by β-decays. ("Ivy Mike" contained five tons of uranium metal used as a tamper around the fusion fuel.) The "classified" discoveries could only be published in 1955 after Ghiorso et al. had "rediscovered" Es and Fm using cyclotron-accelerated 14N ions and neutrons produced by a high-flux reactor in Idaho.

Ghiorso A.
Thompson S.G.
Higgins G.H.
Seaborg G.T.
from BRL
Studier M.H. et al. (ANL)
Browne C.I. et al. (LASL)

1953

Establishing the unified model of the atomic nuclei, shedding light on collective excitations like vibration (a periodic change of the shape of the nucleus) and rotation of the core of a deformed nucleus (around an axis perpendicular to its symmetry axis), while the valence nucleons move on individual orbits.

Bohr A.N.
Mottelson B.L.
Rainwater N.J. (1975-p)

1953-1960

Using proton and deuteron targets in electron scattering experiments it was discovered that nucleons have an inner structure as far as their charge distribution is concerned.

Hofstadter R. (1961-p) et al.

1954

Launching the submarine NAUTILUS #, the first nuclear powered ship of the world. She had been serving the USN for 25 years. In 1958, she was the first ship that ever crossed the north pole.

Rickover H.G.

1954

Further developing Glaser's bubble chamber. Alvarez's hydrogen (bubble) chamber contains liquid hydrogen. When a particle passes through the liquid, it boils hydrogen along its track. The tiny H2 bubbles formed are immediately photographed so that the track can be studied later. Since the chamber contains hydrogen only, interpretation of the tracks is relatively simple, because reactions with protons are only to be considered.

Alvarez L.W. (1968-p)
Crawford F.
Stevenson L.
Wood J.

1955

Production of antiprotons by using the Bevatron #, the proton accelerator of the Berkeley Lab at University of California, Berkeley. Alvarez's hydrogen chamber was used as a detector. Considering the 1932 discovery of positron, at this point the components of a complete antihydrogen atom were ready.

Chamberlain O.
Segrè E.G. (1959-p)
Wiegand C.
Ypsilantis T.

1955

Production of the actinide mendelevium (101Md) by bombarding 253Es with cyclotron-accelerated 4He ions (α-particles). Ghiorso et al. obtained 256Md (T1/2 ≈ 77 min). The most stable mendelevium isotope, 258Md, has a half-life of 52 d. This was about the last element discovered with major contribution from chemistry. This was also the last one produced by using a light projectile (α).

Ghiorso A.
Harvey B.G.
Choppin G.R
Thompson S.G.
Seaborg G.T.

1955-1960

Establishing neutron spectroscopy, a method based on the inelastic scattering of neutrons and used for studying the dynamic properties of condensed phases.

Brockhouse B.N. (1994-p)

1956

Confirmation of the detection of free neutrino (actually electron antineutrino), whose existence had been hypothesized by W.E. Pauli in 1930 to explain the "missing energy" (the continuous energy spectrum) of β-rays. The name "little neutron" was coined by E. Fermi in 1933, one year after Chadwick's discovery of the neutron.

Reines F. (1995-p)
Cowan C.L.
Harrison F.B.
Kruse H.W.,
McGuire A.D.

1956

Designing a number of experiments that are suitable for checking the violation of parity conservation in general (and β decay/weak interaction in particular). The first successful experiment to test the incompleteness of right-left symmetry in the β decay was reported by C.S. Wu, E. Ambler, R.W. Hayward et al. in 1957. (They proved that left-handed electrons coming from the beta emitter 60Co slightly outnumber the right-handed ones.)

Lee T.D.
Yang C.N. (1957-p)

1957

Proving that neutrinos have negative helicity, i.e. their spins point backwards as they propagate. This property is also called left-handedness (see above). Antineutrinos are now known to be right-handed.

Goldhaber M.
Grodzins L.
Sunyar A.W.

1957

Discovery of the antineutron. Considering the discovery of positron in 1932 and that of the antiproton in 1955, at this point all three subatomic components were "available" to build up a complete periodic table of antielements.

Cork B.
Lambertson G.R.
Piccioni O.
Wenzel W.A.

1957

Theoretically showed that all of the chemical elements from carbon to uranium could be produced by nuclear processes in stars starting with the hydrogen and helium produced in the big bang. Fowler also provided calculations for the solar neutrino investigations started a decade later. In a famous 1957 paper called B2FH (B squared F H) after the initials of its authors, the existence of the p- (proton process @), r- (rapid neutron-capture process @), and s-process (slow neutron-capture process) had been predicted. These processes, together with the rp-process (rapid proton-capture process, related with X-ray bursts  @), are of great importance in nucleosynthesis.

Burbidge G.
Burbidge M.
Cameron A.G.W.
Fowler G.A. (1983-p)
Hoyle F.

1957

Launching the synchrophasotron # of the Joint Institute for Nuclear Research (JINR) in Dubna. With the proton energy of 10 GeV, it was the most powerful accelerator in the world at that time.

Veksler V.M.

1958

Discovery and explanation of the recoilless resonance emission and absorption of atomic nuclei in solids. The so-called Mössbauer effect serves as a basis for Mössbauer spectroscopy, a method used among others in chemistry. A miniscule spectrometer was even sent to the Mars # to study iron-bearing rock samples on the spot.

Mössbauer R.L. (1961-p)

1958

Production of the actinide nobelium (102No) by bombarding 246Cm (actually 244Cm that was the major component at 95%) with accelerated 12C ions. Ghiorso et al. supposed they obtained 254No with 3 s for half-life. Actually they obtained 252No (T1/2 ≈ 2.3 s), and the half-life of 254No is now known to be 50 s. The most stable isotope of nobelium, 259No, has a half-life of 58 min. This element was the first one of a series produced by hot fusion using heavy ions as projectiles.

Ghiorso A.
Seaborg G.T.
Sikkeland T.
Walton J.R.

1958

Proposing 1/12 of the mass of a 12C atom as a unit in which atomic masses are measured. The unified atomic mass unit (u) was accepted by both IUPAC and IUPAP in 1960.

Kohman T.P.
Mattauch J.H.E.
Wapstra A.H.

1959

Radioimmunoassay (RIA) is accepted by the scientific community. The idea is that the concentration of the unknown unlabeled antigen is obtained by comparing its inhibitory effect on the binding of radioactively labeled antigen to specific antibody with the inhibitory effect of known standards. R. is for Rosalyn, another female Nobel Laureate of the few.

Yalow R. (1977-m)

1959

Proposing the nuclear reaction model later named deep inelastic collision (grazing collision) involving heavy ions. The nuclei stick together forming a transitory complex, and then break up again fission-like due to Coulomb repulsion before a real compound nucleus could be formed.

Kaufmann R.
Wolfgang R.

1960

Discovery of muonium (Mu), an atom-like bound state of a positive muon μ+ and a negatron e-. Muonium, one of the exotic atoms, is quite similar to hydrogen both in size and chemical properties (much more similar than, e.g., positronium). Chemical applications include muon spin resonance (μSR).

Hughes V.W.
McColm D.W.
Prepost R.
Ziock K.

1961

Launching the first navigational satellite (Navy Transit 4A) for which electrical power was provided by a "radionuclide thermoelectric generator". RTGs directly convert the heat generated by the decay of plutonium-238 oxide to electricity.

 

1961

Production of lawrencium (103Lr), heaviest of the actinides, by bombarding 249,250,251,252Cf with 10,11B ions accelerated by the linear accelerator HILAC. (It would have been more appropriate perhaps to use a cyclotron instead invented by E.O. Lawrence, eponym of lawrencium.) Ghiorso et al. obtained 258Lr (T1/2 ≈ 4.1 s). For the most stable isotope, 262Lr, T1/2 ≈ 3.6 h.

Ghiorso A.
Larsh A.E.
Latimer R.M.
Sikkeland T.

1962

Discovery of the muon neutrino νμ whose existence (together with that of the νe) demonstrates that leptons come in pairs (i.e., e with νe, μ with νμ and - as it turned out later - τ with ντ).

Lederman L.M.
Schwartz M.
Steinberger J. (1988-p)

1962

Discovery of nuclear shape isomerism. The first elongated shape isomer decaying with SF with very short half-life (14 ms) was 242fAm. The shapes are stabilized by shell effects.

Polikanov S.M.
Druin V.A.
Karnaukhov V.A. et al.

1963

Discovery of muonic molecules pμp and pμd. Bleser et al. studied the fusion reaction p + d → 3He + γ catalyzed by muons from the Nevis synchrocyclotron stopped in liquid hydrogen. Neon added to the target trapped the muons forming muonic atoms with them. (In muonic atoms an electron is replaced by a negative muon μ-.)

Bleser E.J.
Anderson E.W.
Lederman L.M.
Meyer S.L. et al.

1963-1964

Creating the quark (q) concept #. According to the original idea three such particles (u, d, and s, i.e. up, down, and strange) were just enough to build up hadrons (i.e. mesons # and baryons #) and explain their properties. (The name quark comes from the book Finnegans Wake by James Joyce #.) This concept was of great use in classifying and predicting particles. One of the predicted particles, the omega minus baryon (Ω) was supposed to be composed of three s quarks. To satisfy the Pauli principle demanding that the three fermions should be in different states, a new quantum-state descriptor, the color (red, green and blue - RGB) was created. Quark confinement translates to the rule that only colorless/white particles can be observed such as mesons (built from a quark and an antiquark of complementary colors, e.g. R and C) and baryons (built from three quarks of different RGB colors).

Gell-Mann M. (1969-p)
Zweig G. et al.

1964

Discovery of the strange (s) quark #, a 2nd generation quark at BNL while proving the existence of the omega minus baryon) named and theoretically predicted by M. Gell-Mann.

Palmer R.
Samios N.
Shutt R.

1964

Prediction of a peculiar particle named the Higgs boson (H0) which is supposed to be the source of the mass of other particles.

Higgs P.

1964

Experimental evidence for the violation of CP symmetry (charge and parity symmetry). It was found that the long-lived neutral K meson (KL) decayed into two charged pions, a decay mode forbidden by CP symmetry. In simple terms, the results mean that matter and antimatter are not completely symmetric (as regards weak interaction), a conclusion very important for cosmology.

Christenson J.
Cronin J.W.
Fitch V.L. (1980-p)
Turlay R.

1965

Discovery of cosmic microwave background (CMB) radiation, an important proof of Big Bang theory and the evolution of matter. (The Big Bang theory itself had been advocated by the Belgian astronomer G.-H. Lemaître since 1927. He referred to his theory as "the Cosmic Egg exploding at the moment of the creation", a proper metaphor for a Roman Catholic priest what he was.)

Penzias A.A.
Wilson R.W. (1978-p)

1967

First observation of the solar neutrino problem, namely, that the number of neutrinos coming from the Sun is only 1/3 of what was expected. The detector built in the Homestake Gold Mine was based on the reaction ν + 37Cl  e- + 37Ar. It contained 380 m3 of C2Cl4, from which the radioactive 37Ar (T1/2=35 d) was extracted with 36Ar every 2-3 months. Over a period of 25 years, 2200 37Ar atoms had been detected! (Davis Jr. also proved earlier that the neutrino and the antineutrino are different particles.)

Davis Jr. R. (2002-p)

1967

Explaining the asymmetric fission # # of nuclei by introducing shell corrections to the liquid-drop energies during the deformation process that leads to fission.

Strutinsky V.M.

1967-1970

First evidence for the existence of the up (u) quark and the down (d) quark, representing the 1st generation of quarks. The proof was provided by deep inelastic scattering experiments at SLAC. The u quark (charge/e = 2/3) is the one that makes the proton p (uud) a positive particle. The d quark (charge/e = -1/3) makes the neutron n (udd) neutral by counterbalancing the charge of u. Neutral particles, gluons, binding quarks in nucleons @ were also discovered in the same series of experimental/theoretical studies.

Bjorken J.D.
Feynman R.P.
Friedman J.I.
Kendall H.W.
Taylor R.E. (1990-p) et al.

1968

Reaching the temperature equivalent to 1 keV (11.6 MK) in the Tokamak, a Soviet fusion reactor using magnetic confinement for keeping away plasma from the walls of the reactor chamber.

 

1968

Inventing the multiwire proportional chamber for the detection of the track of high-energy particles.

Charpak G. (1992-p)

1969

Production of rutherfordium (104Rf), the lightest of the transactinides, by bombarding 249Cf with 12C ions. Ghiorso et al. obtained 257Rf (T1/2 ≈ 4.7 s). The most stable rutherfordium isotope produced as of 2006, 263Rf, has a half-life of 10 min.
Flerov et al. also claimed the credit for the discovery on account of their 1964 experiment in which 242Pu was bombarded with 22Ne ions. (Until 1997, Rf was also known as kurchatovium, Ku.)

Ghiorso A.
Nurmia M. et al.
Flerov G.N.
Oganessian Yu.Ts. et al.

1970

Production of the transactinide dubnium (105Db) by bombarding 249Cf with 15N ions. Ghiorso et al. obtained 260Db (T1/2 ≈ 1.5 s).
Dubna scientists (Flerov et al.) have also claimed the credit for the discovery on account of their experiment in which 243Am was bombarded with 22Ne ions yielding 261Db (T1/2 ≈ 1.8 s).

Ghiorso A. et al.
Flerov G.N. et al.

1970

Postulation of the existence of a fourth quark (c for charm). Experimental proof followed 4-6 years later in connection with the discovery and the interpretation of the J/ψ particle.

Glashow S.
Iliopoulos J
Maiani L.

1970

First report on proton radioactivity. The observation was made with the nuclear isomer 53mCo. Proton decay @ from a ground-state nuclide (151Lu) was first observed in 1981 by S. Hoffmann et al. (β-delayed proton emission @ was discovered in 1964.)

Jackson K.P.
Cardinal C.U.
Evans H.C. et al.

1968-1972

Elucidation of the quantum structure of electroweak interaction. The latter is considered as unification of the electromagnetic interaction propagated by photons (g) and the weak interaction # propagated by W+, W- and Z0 bosons.

't Hooft G.
Veltman M.J.G. (1999-p)

1972

Discovery of ancient nuclear reactor of natural origin at Oklo, Gabon (Oklo fossil reactor). It had operated for hundreds of millennia some 1.7 Ga ago. The possibility of the existence of natural fission reactors of similar type was predicted by P.K. Kuroda in 1956. In 1993, J.M. Herndon pointed out the possibility of another type of fission reactor that is supposed to be operating in the center of the Earth's core (geo-reactor). Its existence, however, is controversial.

Bodu R.
Bouzigues H.
Morin N.
Pfiffelmann J.P.

1973

Theory explaining asymptotic freedom of quarks, i.e. when they get close together the strong force acting between them vanishes. On the other hand, quarks are confined (e.g. in the nucleons in groups of three), i.e. they cannot be separated from each other because the same strong (color) force gets stronger with distance.

Gross D.J.
Politzer H.D.
Wilczek F.A. (2004-p)

1973

Postulation of the existence of a 3rd generation of quarks consisting of the b (bottom) and t (top) quarks.

Kobayashi M.
Maskawa T.

1973

Creation of an electroweak theory by assuming four boson propagators: the mass-less photon (γ) and three heavy bosons (W+, W-, and Z0). Thus the Standard Model # of particles and interactions got completed as a theory. The hypothesized bosons were found ten years later.

Glashow S.L.
Salam A.
Weinberg S. (1979-p)

1974

Producing the transactinide seaborgium (106Sg) by bombarding 249Cf with 18O ions in the Super-Heavy Ion Linear Accelerator. Ghiorso et al. obtained 263Sg (T1/2 ≈ 1 s.). Since transactinides are very short-lived and the atoms are produced rather infrequently one by one, single-atom chemistry is an important issue here. This was the heaviest element produced by hot fusion (during which several neutrons evaporate).

Ghiorso A.
Nitshke J.M.
Alonso C.T.
Alonso J.R.
Nurmia M. et al.

1974

Simultaneous discovery of the J/ψ particle at SLAC (2.6-8 GeV electon-positron storage ring, SPEAR #) and BNL (high-intensity proton beam from the Alternating Gradient Synchrotron, AGS #). By 1976, J/ψ got interpreted as charmonium (on the analogy of positronium e-e+), consisting of a c quark (charm quark #, predicted in 1970), representing the 2nd generation of quarks, and its antiparticle.

Richter B.
Ting S.C.C. (1976-p)

1974-1977

Discovery of the tau lepton (also called tauon), τ, representing the 3rd generation of leptons (electron e: 1st generation, muon μ: 2nd generation). Contrary to its "family name" lepton (leptos means delicate) the tauon's mass is mτ ≈ 3477 me, i.e., it is almost as heavy as two 1H (protium) atoms or a 2H (deuterium) atom.

Pearl M.L. (1995-p) et al.

1977

Discovery of the bottom (b) quark #, the fifth quark predicted by M. Kobayashi and T. Maskawa. Fermilab scientists actually produced Υ (upsilon) particles which were immediately recognized as a composition of a b/anti-b pair (i.e. bottomonium).

Lederman L.M. et al.

1981

Production of the transactinide bohrium (107Bh) by bombarding 209Bi with 54Cr ions at GSI, Darmstadt. Münzenberg et al. obtained six atoms of 262Bh (T1/2 ≈ 8 ms). The most stable bohrium isotope, 272Bh, has a half-life of 6-20 s. (The discovery of element 107 was first announced by JINR, Dubna, in 1976.) This was the first element produced by cold fusion @ (a term introduced by Oganessian et al. in 1975 for targets like Pb and Bi having closed nucleon shells). It is not to be confused with the controversial "cold fusion" supposedly observed at room temperature in 1989 using electrolysis.

Münzenberg G.
Hofmann S.
Heßberger F.P.
Reisdorf W.
Schmidt K-H. et al.

1982

Production of the transactinide meitnerium (109Mt) by bombarding 209Bi with 58Fe ions using a high-energy linear accelerator at GSI, Darmstadt. Münzenberg et al. obtained 266Mt (T1/2 ≈ 1.7 ms). The most stable meitnerium isotope, 276Mt, has a half-life of about 0.5-1.5 s.

Münzenberg G.
Armbruster P.
Heßberger F.P.
Hofmann S.
Poppensieker K. et al.

1983

Experimental observation of the vector bosons W+, W-, and Z0, the propagators of the weak interaction which were predicted by S.L. Glashow, A. Salam and S. Weinberg about a decade earlier. They turned out really massive, in the order of a Sr or a Mo atom, or - to take a more familiar example - two ethanol molecules.

Rubbia C.
van der Meer S. (1984-p)

1984

Production of the transactinide hassium (108Hs) by bombarding 208Pb with 58Fe ions using a linear accelerator at GSI, Darmstadt, with contribution from Dubna. Münzenberg et al. obtained 265Hs (T1/2 ≈ 2 ms). The discovery was convincingly confirmed by Hofmann et al. in 1989.

Münzenberg G.
Armbruster P.
Folger H.
Heßberger F.P.
Hofmann S. et al.

1984

Discovery of cluster decay (heavy-ion emission) of heavy nuclides with 223Ra that produces 14C. (Later on spontaneous however very rare emission of still heavier clusters such as 24Ne and 28Mg was also observed.)

Rose H.J.
Jones G.A.

1984

Observation of β-delayed triton emission (βt, t = 3H+) in 11Li. The latter turned out a little later to be one of the halo nuclei # #. According to P.G. Hansen and B. Jonson (1987), the extremely large nuclear radius of 11Li, e.g., can be explained by the halo effect, i.e. it can be visualized as a binary system consisting of a 9Li core surrounded by a weakly bound pair of neutrons.

Langevin M.
Détraz C.
Epherre M. et al.

1986

Explosion in the Chernobyl nuclear power plant @ in Pripyat, Ukraine, then part of USSR. It was the worst accident in the history of nuclear power production, which (combined with the effort of the authorities to cover the facts) caused lots of casualties and physical damage. It also made the adjective "nuclear" a nasty word again, making people suspicious of anything labeled with it. This was the third major accident following those in the Three Mile Island nuclear power plant (1979) and in the Windscale reactor (1957).

 

1987

First observation of double beta decay @ (2β or ββ) with 82Se (T1/2 ≈ 1020 a), when two neutrons simultaneously transform to protons emitting two electrons and two antineutrinos. Its longer abbreviation is ββ2ν or 2νββ to differentiate it from neutrinoless double beta decay (0νββ), a decay mode of considerable theoretical importance that has not been found so far.

Elliott S.R.
Hahn A.H.
Moe M.K.

1987

Kamiokande II, a direction-sensitive neutrino detector built for observing solar neutrinos, (and two other ν-detectors) detected a burst of neutrinos (duration: 10 s) from the supernova explosion 1987A #. The neutrinos were registered 3 h before the first optical evidence (exposure of a photographic plate) was collected.

Koshiba M. et al.

1992

Discovery of bound-beta radioactivity βb meaning that stable nuclides like 163Dy become unstable when they get completely stripped of their atomic electrons. The half-life of 163Dy66+ ions is a mere 50 days, whereas neutral dysprosium is stable. In a way βb-decay is a reversed EC, because the electron emitted gets trapped by one of the atomic shells.

Jung M. et al.

1994

Production of the transactinide darmstadtium (110Ds) by bombarding 208Pb with 62Ni ions using a linear accelerator at GSI, Darmstadt. Hofmann et al. obtained 269Ds (T1/2 ≈ 100-400 ľs). Its most stable isotope, 281Ds, has a half-life of 11 s.

Hofmann S.
Armbruster P.
Folger H.
Heßberger F.P. et al.

1995

Discovery of the transactinide roentgenium (111Rg) by bombarding a 209Bi target with 64Ni ions using a linear accelerator at GSI, Darmstadt. Hofmann et al. obtained 272Rg (T1/2 ≈ 3-5 ms). The most stable isotope, 280Rg, has a half-life of about 2-8 s. The name roentgenium was approved in 2004. As of 2006 this is the heaviest element having a final name approved by IUPAC.

Hofmann S.
Armbruster P.
Folger H.
Heßberger F.P. et al.

1995

Discovery of the top (t) quark #, the last undiscovered quark belonging to the 3rd generation at Fermilab (director: J. Peoples) using the proton-antiproton collider Tevatron @. !!! It was announced as a simultaneous result of the efforts of several hundred scientists working in two competing teams represented by P. Grannis and H. Montgomery (DO Collaboration), and B. Carithers and G. Bellettini (CDF Collaboration). The t quark is a very massive particle - it "weighs" a little more than 10 H2O molecules.

Carithers B. et al.
Grannis P. et al.

1996

Claim of discovery of ununbium (112Uub) - a provisional IUPAC name for 112X - by bombarding a 208Pb target with 70Zn ions using a linear accelerator at GSI, Darmstadt, with contributors from JINR, Dubna. Hofmann et al. obtained 277Uub (T1/2 ≈ 450-1400 ľs).

Hofmann S.
Armbruster P.
Folger H.
Heßberger F.P. et al.

1998

Experimental proof of neutrino oscillation (neutrino mixing, change of flavor) involving 2nd and 3rd generation neutrinos. The Super-Kamiokande observations # show that a large part of muon neutrinos νμ produced in the atmosphere change into tau neutrinos ντ before they could reach the Earth's surface. Neutrino oscillation also means that neutrinos cannot be mass-less # like photons traveling at the speed of light.

Koshiba M. (2002-p)

1999

Claimed production of ununquadium (114Uuq) by bombarding a 242,244Pu target with 48Ca ions. Oganessian et al. obtained 289Uuq with a half-life between 1.9-3.8 s (T1/2 ≈ 2.6 s). They also claim to have observed the decay @ of 288Uuq.

Oganessian Yu.Ts.
Abdullin F.Sh.
Lobanov Yu.V.
Polyakov A.N.
Utyonkov V.K. et al.

1999

Determination of the number of neutrino types. The four LEP experiments resulted in Nν = 2.984 +/- 0.008 that translates to 3.

Mnich J. et al.

2000

Announcing the production of quark-gluon plasma @ at CERN by colliding high-energy lead ions.

 

2000

Direct evidence for the existence of the tau neutrino ντ (which is the 3rd and the last type). The last of the particles in the Standard Model of elementary particles # was discovered by an international collaboration of 54 physicists at Fermilab, after a three-year analysis of data from the Direct Observation of the Nu Tau (DONUT #) experiment. The discovery of all SM particles took a little more than a century.

Kodama K. et al.

2000

Claimed production of ununhexium (116Uuh) by bombarding 248Cm with cyclotron-accelerated 48Ca ions. Oganessian et al. obtained 292Uuh (T1/2 ≈ 18 ms), which was identified by its decay chain. Uuh is the heaviest element so far (as of 2006) whose existence has been reported and reproduced.

Oganessian Yu.Ts.
Abdullin F.Sh.
Lobanov Yu.V.
Polyakov A.N.
Utyonkov V.K. et al.

2002

The Sudbury Neutrino Observatory # (SNO) confirmed that the flux of all neutrinos (νe etc.) coming from the Sun matches the prediction of the solar standard model for electron neutrinos alone. However, only half of them are electron neutrinos. This solved the solar neutrino problem. (Fusion processes in the Sun only produce νe. Physicists were puzzled when it turned out in 1967 that only 1/3-1/2 of the predicted number reaches the Earth. Now, if they can change into other types during the journey, the puzzle is solved.)

 

2002

Observation of two-proton decay in ground-state 45Fe, a proton-rich nuclide near the proton dripline. The half-life found is quite long (about 5 ms). (The first report on beta-delayed two-proton decay of 22Al was published in 1981 by M.D. Cable, J. Honkanen et al.)

Giovinazzo J.
de Oliveira Santos F.
Grzywacz R.
Borcea C.
Brown B.A. et al.

2003 It was proved by experiment that bismuth is a radioactive element. Its only naturally occurring isotope, 209Bi, undergoes 3.137 MeV α decay with a half life of 1.9×1019 a to produce 205Tl, the more abundant of the two stable isotopes of thallium.

de Marcillac P.
Coron N.
Dambier G.
Leblanc J.
Moalic J-P.

2003

Explanation of the extreme radiation resistance of Deinococcus radiodurans, called Conan the Bacterium by its fans ever since its 1956 discovery in γ-ray-sterilized canned meat that got spoiled. The red bacterium can withstand a thousand times higher dose than any other life form and three thousand times more than us humans. The key to its high radioresistance is supposed to be the ringlike structure of the genome.

Levin-Zaidman S.
Englander J.
Shimoni E.
Sharma A.K.
Minton K.W.
Minsky A.

2004

Announcement of the production of ununtrium (113Uut) at RIKEN by bombarding 209Bi with cyclotron-accelerated 70Zn ions. Morita et al. obtained 278Uut with T1/2 ≈ 0.24 ms (0.13-1.38 ms). As of 2006 this element would be the first one discovered by Japanese scientists.

Morita K.
Akiyama T.
Goto S-i.
Kaji D.
Morimoto K. et al

2004

Collaborating Russian (JINR) and American (GTSI) scientists lead by Oganessian reported the synthesis of ununpentium (115Uup) in the reaction 243Am(48Ca,xn)287, 288Uup. The half-life of  287Uup was estimated 18-187 ms (T1/2 ≈ 32 ms), while that of 288Uup was 57-192 ms (T1/2 ≈ 87 ms).

Oganessian Yu.Ts.
Utyonkov V.K. et al. (JINR)
Moody K.J.
Patin J.B. et al. (GTSI)

2006

Collaborating Russian (JINR) and American (GTSI) scientists lead by Oganessian reported the synthesis of ununoctium (118Uuo) in the reaction 249Cf(48Ca,3n)294Uuo. The half-life of the α-decaying even-even isotope 294Uuo was estimated 0.57-1.96 ms (T1/2 ≈ 0.89 ms).

Oganessian Yu.Ts.
Utyonkov V.K. et al. (JINR)
Moody K.J.
Patin J.B. et al. (GTSI)

2006

A Princeton-led group reported discovery of bacteria 2.8 km underground (Mponeng Gold Mine, South Africa) deriving energy from the radioactivity of rocks rather than from sunlight. The life of these sulfate reducers (related to Desulfotomaculum) depends on the hydrogen produced by the radiolysis of water.

Lin L-H.
Wang P-L.
Rumble D.
Lippmann-Pipke J.
Boice E. et al.

2007

An IUPAC/IUPAP Joint Working Party is considering claims for the discovery of the "transroentgenium" elements with Z = 112, 113, 114, 115, 116, and 118.

Karol P.J. et al.

2008

The 27 km long Large Hadron Collider (LHC) at CERN starts test runs in preparation for p-p collision experiments to study the conditions right after the Big Bang. The final collision energy is planned to be 14 TeV. To achieve this, proton beams moving in the opposite direction have to be accelerated to 7 TeV before head-on collision takes place between them.

 
2009-2010 On July 14, 2009, press release from GSI, Darmstadt, suggested the name copernicium (Cp) for element 112Uub whose 1996 claim of discovery was accepted by IUPAC in May 2009. Later that year the suggested symbol was changed to Cn as it turned out that Cp was already in use till 1949 indicating cassiopeium, a synonimous name for lutetium, now outdated. On February 20, 2010, IUPAC announces official acceptance !!! of the name and symbol.  
2011 Discovery of the elements with Z = 114 and 116 has been accepted and the priority assigned by the IUPAC/IUPAP Joint Working Party (JWP) on the basis of several papers published by the Dubna-Livermore collaboration (Oganessian et al., 2004). See also the IUPAC report. The names of the elements would be proposed by the collaboration.

 

2011 Gran Sasso: Claimed discovery of muon neutrinos whose speed exceeds the speed of light in empty space. The relative difference was claimed to be significantly larger than the statistical and systematic error together. (See some comments: Neutrino stories move faster than the speed of science.) The claim was withdrawn by CERN in a press release on June 8, 2012. Adam T. et al.
2012 May 30, 2012: IUPAC has officially approved the name flerovium, with symbol Fl, for the element of atomic number 114 and the name livermorium, with symbol Lv, for the element of atomic number 116. Priority for the discovery of these elements was assigned, in accordance with the agreed criteria, to the collaboration between the Joint Institute for Nuclear Research (Dubna, Russia) and the Lawrence Livermore National Laboratory (Livermore, California, USA).  
2012 July 4, 2012, CERN press release: claimed observation of particle consistent with long-sought Higgs boson. Publication in Physics Letters B on 17 September 2012: Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC. CMS Collaboration


Last update: . (The last row checked by that date is marked by )

Courtesy UNESCO-EOLSS http://www.eolss.net. The original version of the above table was compiled for the UNESCO-EOLSS Theme 6.104. Radiochemistry and Nuclear Chemistry [1].

[1] Sándor Nagy,(2007),RADIOCHEMISTRY AND NUCLEAR CHEMISTRY, in Radiochemistry and Nuclear Chemistry, [Ed. Sándor Nagy], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net]

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