1896
Henri Becquerel discovered the phenomenon of radioactivity. He found that uranium salt wrapped in a paper emitted certain penetrating radiations which affected photographic plate. He also found that these radiations were highly penetrating and causes scintillations on fluorescent screen.
Rutherford showed later that the radiations from the salt were capable of ionising a gas. A few years later Madame Marie Curie and her husband Pierre Curie discovered the highly radioactive elements radium and polonium.
1903
When a radioactive disintegration occurs in an element with the emission of alpha or beta particles, the original element is called parent and that remains after disintegration is called daughter, which is also radioactive in nature. Rutherford and Soddy proposed that the nature of daughter could be inferred from the nature of the parent and the particle emitted.
1905
Albert Einstein proposed the special theory of relativity. The special theory of relativity deals with objects and systems, which are either moving at a constant speed with respect to one another or at rest.
1911
Lord Rutherford carried out a series of experiments on the scattering of alpha particles by matter in the form of thin film. This revealed the existence of a positively charged nucleus at the centre of atom and ultimately led to the present atomic theory. Rutherford found that the atom has small positively charged nucleus at its centre.
All positive charges of an atom and most of the mass of the atom are concentrated in a very small central region of radius 10-14 m which is known as nucleus. Electrons have no place inside the nucleus. The electrons revolve around this nucleus at some distance away.
1911
Lise Meitner and Otto Hahn performed an experiment showed that the energies of electrons emitted by beta decay had a continuous rather than discrete spectrum. This was in apparent contradiction to the law of conservation of energy, as it appeared that energy was lost in the beta decay process.
1913
Soddy and Fajan discovered the displacement law which governs the radioactive decays. During a radioactive disintegration, the nucleus which undergoes disintegration is called a parent nucleus and which remains after the disintegration is called a daughter nucleus.
When a radioactive element disintegrates by emitting an alpha particle, the atomic number decreases by two and mass number decreases by four and becomes another element.When a radioactive element disintegrates by emitting a beta particle, the atomic number increases by one and the mass number remains the same and becomes another element. When a radioactive element emits gamma rays, only the energy level of the nucleus changes and the atomic number and mass number remain the same.
1919
Rutherford made the first successful attempt to convert one element into anther in the laboratory. The process of producing new stable nuclei from the other stable nucleus is known as the artificial transmutation or artificial disintegration of elements.
1921
O. Hahn discovered the phenomenon of nuclear isomerism. He found that UX2 and UZ both have the same atomic number and the same mass number but have different half lives and emit different radiations.
1924
Louis de Broglie postulated that nature is symmetrical in many ways and the universe is made of radiation (light) and matter (particle). Louis de Broglie suggested that similar to light (Photon), an electron or any other material particle like proton must also exhibit the wave like properties when they are in motion. The wave associated with these material particles are known as matter waves or de Broglie waves.
1924
Satyendra Nath Bose worked on quantum mechanics and provided the foundation for Bose-Einstein statistics, the theory of the Bose-Einstein condensate, and the discovery of the boson
1925
Heisenberg put forward the quantum theoretical mechanics based exclusively on relationship between quantities observable in principle.
1925
Wolfgang Pauli outlined the “Pauli exclusion principle” which states that no two identical fermions may occupy the same quantum state simultaneously.
1926
Enrico Fermi and Paul Dirac worked on statistics for fermions introduced Fermi-Dirac statistics
1926
Erwin Schrödinger originally proposed the basic equation for the wave mechanics. Schrödinger wave equation describes the wave nature of a particle in mathematical form. Schrödinger connected the expressions of de-Broglie wavelength with the classical wave equation for a moving particle and obtained a new wave equation.
1926
Heisenberg formulated his famous uncertainty principle. According to Heisenberg’s uncertainty principle, the position and momentum of a particle say electron cannot be determined simultaneously to any desired degree of accuracy.
1927
Davisson and Germer and independently G.P.Thomson observed electron diffraction pattern produced by metal foils which established the existence of the de Broglie wave. The two experiments performed by Davisson and Germer and G.P.Thomson proved accelerated electrons behave like wave form.
1928
Gamow in Germany and Gurney and Condon in USA reported the first major application in quantum mechanics namely the barrier leakage interpretation of the natural radioactive decay of some elements emitting alpha particles.
1929
Robert J. Van de Graaff designed an electrostatic machine which produces large electrostatic potential difference of the order of 107 V. The working of Van de Graaff generator is based on the principle of electrostatic induction and action of points.
1931
Joly and Rutherford suggested uranium dating to determine the age of some rocks. The naturally occurring isotopes of uranium-238 and uranium-235 decay very slowly and ultimately become isotopes of lead but not the common isotope of lead-208. If we can determine the percentage of radiogenic lead isotopes and uranium isotopes present in a rock sample, based on the half life of uranium isotopes, we can calculate the exact ages of these rocks.
1931
Pauli suggested the existence of the neutrino in order to explain the continuous beta ray spectrum and in 1934 Fermi developed the famous theory of beta decay.
1932
Chadwick suggested that an uncharged particle called neutron were emitted when beryllium was bombarded with alpha particles of energy 5 MeV.
1932
The first electron microscope was constructed. Electrons can behave like a waveform when they are accelerated by very high electric potential difference. The electron wave of very short wavelength is made use in the construction of electron microscope.
1932
J.D Cockroft and E.T.Walton constructed a dc particle accelerator in which a stream of electrons was used to ionize hydrogen gas and produce protons.
1932
Professor E.O.Lawrance and M.S. Livingstone devised the first cyclotron at the University of California at Berkeley. The cyclotron is a device to accelerate positively charged particles in successive steps under combined influence of electric and magnetic fields along circular or spiral trajectories.
1932
Carl D. Anderson experimentally proved the existence of the positron which is the antiparticle of electron. Positron has the same mass of an electron and a positive charge as the electronic charge.
1934
Fermi developed a theory to explain the continuous beta ray spectrum. This theory is called the neutrino theory of beta decay. According to this theory, a beta particle and a neutrino are created in the nucleus and both are emitted simultaneously. In beta disintegration, the amount of energy released is equal to the end point energy. The energy is shared between beta particle and neutrino.
1934
Curie and Joiot discovered the artificial or induced radioactivity. They were studying the disintegration of light elements by alpha particles. When aluminium was bombarded with alpha particles, the target continued to emit radiations even after the source of alpha particles had been removed.
1934
Enrico Fermi discovered that bombarding uranium by neutron produced several elements of beta ray activities with different half lives.
1935
Yukawa proposed a theory to explain the binding forces between neutrons and protons known as meson theory of nuclear forces. According to this theory, there exists a meson cloud surrounding the neutrons and protons. There are three kinds of mesons exist in the meson cloud namely positively charged, negatively charged and neutrally charged mesons.
The theory also predicts that protons and neutrons do not have their independent existence inside the nucleus. The mesons are supposed to exchange between nucleons, thereby changing their identity equally fast and responsible for making the nucleons bound inside the nucleus.
1936
Neils Bohr has proposed liquid drop nuclear model. In liquid drop model, the forces acting inside the nucleus are assumed to be analogous to the molecular forces in a droplet of liquid. Neils Bohr has observed that there are certain similarities between an atomic nucleus and a liquid drop. Using liquid drop model, the calculation of atomic masses and binding energies can be done with good accuracy.
1936
Carl D. Anderson discovered muons while he studied cosmic radiation. The μ-meson (muon) is 207 times heavier than the electron, but carries the same change. There exist negative as well as positive μ-mesons, but there are no neutral μ-mesons.
1937
Carl Anderson experimentally proved the existence of the pion or π-mesons. The three types of mesons πo, π- and π+ are responsible for the interaction between protons and neutrons inside the nucleus.
1938
Hahn and Strassman showed when uranium is bombarded by neutrons, radioactive elements of barium with atomic number Z = 56 (56 Ba141) and krypton with atomic number Z = 36 (36Kr92) were produced. Meitner and Frisch suggested that the process of uranium splits into two lighter nuclei barium and krypton when bombarded with neutron is known as nuclear fission process.
1939
Bohr and Wheeler have given the first thorough theoretical treatment of the fission process based on the liquid drop model. However, this model fails to explain the extraordinary stability of certain nuclei, spin and magnetic moment.
1939
A.Langsdroff designed the diffusion cloud chamber. However the diffusion cloud chamber also works on the principle of condensation of supersaturated water vapours on the ions left behind by ionizing particles.
1939
Bethe suggested the carbon nitrogen cycle and proton-proton cycle as the most important nuclear reactions for the release of energy by fusion.
1939
Leó Szilárd and Enrico Fermi discovered the chain reaction. The chain reaction takes place during fission process multiplies the neutrons and reaction continues till the last atom of uranium exist
1941
The cyclotron cannot be used to accelerate electrons as their relativistic mass increase even at low energies. In 1941, D.W.Kerst designed and developed betaton at University of Illinois. The name itself suggests that betatron is specifically meant for accelerating electrons only.
1942
Enrico Fermi created the first artificial self-sustaining nuclear chain reaction, called Chicago Pile-1 (CP-1), at the University of Chicago on December 2, 1942.
1942
The first reactor was built as a demonstration in 1942, by Enrico Fermi at University of Chicago USA. A nuclear reactor is an example for controlled chain reaction in which the nuclear fission reaction takes place in a self sustained and controlled manner.
1945
Over the period of six years, from 1939 to 1945, more than $2 billion was spent during the history of the Manhattan Project. The formulas for refining uranium and putting together a working atomic bomb were created and seen to their logical ends by some of the greatest minds of our time. Chief among the people who unleashed the power of the atom was Robert Oppenheimer, who oversaw the project from conception to completion.
Scientists who invented the atomic bomb under the Manhattan project are Robert Oppenheimer, David Bohm, Leo Szilard, Eugene Wigner, Otto Frisch, Rudolf Peierls, Felix Bloch, Niels Bohr, Emilio Segre, James Franck, Enrico Fermi, Klaus Fuchs and Edward Teller.
1945
From the Manhattan Project, the first nuclear fission explosion was carried out on July 16, 1945 in the Trinity test in New Mexico.
1947
G. D. Rochester and C. C. Butler published two cloud chamber photographs of cosmic ray-induced events, one showing what appeared to be a neutral particle decaying into two charged pions, and one which appeared to be a charged particle decaying into a charged pion and something neutral. The estimated mass of the new particles was about half a proton's mass and they were soon given the name kaons.
1948
Maria Gopert Meyer developed the model and in 1949, O.Haxel, J.H.D.Jensen and H.E.Suess independently showed that the nuclei containing magic numbered (2,8,20,28,50,82,126) protons or neutrons exhibited very high stability.
According to shell model, the nucleus is consisting of definite energy levels or shells similar to electron shells in an atom. The total number of protons and neutrons are distributed in different sets energy levels. The number of protons and neutrons in each shell is limited based on Pauli’s exclusion principle.
1950
Rainwater pointed out that if a nuclide has a large quadrupole moment its closed core is never spherical as expected in the shell model. It gets deformed.
1951
Edward Teller and Stanisław Ulam of United States developed the first Hydrogen bomb and tested it at Enewetak atoll on 1st November 1952. The Soviet Union first tested an Hydrogen bomb in 1953, followed by Britain in 1957, China in 1967, and France in 1968. The most modern nuclear weapon, Hydrogen bomb employs both fusion and fission. The Teller–Ulam design is the nuclear weapon design concept used in most of the world's nuclear weapons.
1952
A.Bohr and Mottleson proposed the collective model of the nucleus. In the shell model there is a core made up of paired nucleons. This core may be spherically symmetric or axially symmetric. The collective model assumes the nucleus as consisiting of even-even core plus one or more nucleons moving in the shell model orbits under the interaction of potential produced by the core.
The deformation of the nucleus is attributed to the polarizing action of one or more loosely bound nucleons on the remaining nucleus. The nucleons move in a potential which is not spherically symmetrical.
1952
D.A.Glaser invented bubble chamber which has assumed great importance in the study of minute details of high energy nuclear events. In this instrument the tracks consists of series of closely spaced bubbles which develop on the ions produced by the passage of charged particles through the superheated liquid contained in the chamber.
1955 & 1956
Murray Gell-Mann and Kazuhiko Nishijima independently derived the Gell-Mann–Nishijima formula, which relates the baryon number B, the strangeness S, and the isospin Iz of hadrons to the charge Q, eventually leading to the systematic categorization of hadrons and, ultimately, the quark model of hadron composition.
1956
P. Kuroda predicted that self-sustaining nuclear chain reactions should occur in natural uranium deposits.
1956
Clyde L. Cowan and Frederick Reines experimentally proved the existence of the neutrino.
1959
Japanese scientists Fukui and Miyamoto developed the spark chamber which detects high energy particle events. It combines some of the advantages of triggered track detectors and counters. Its operation depends on the stability of an ionized gas against spark breakdown.
1962
Murray Gell-Mann and Yuval Ne'eman independently classified the hadrons according to a system that Gell-Mann called the "Eightfold Way," and which ultimately led to the quark model (1964) of hadron composition.
1964
Murray Gell-Mann and George Zweig independently proposed the quark model of hadrons, predicting the arbitrarily named up, down, and strange quarks. Gell-Mann is credited with coining the term "quark," which he found in James Joyce's book Finnegans Wake.
1964
Sheldon Lee Glashow and James Bjorken predicted the existence of the charm quark. The addition was proposed because it allowed for a better description of the weak interaction (the mechanism that allows quarks and other particles to decay), equalized the number of known quarks with the number of known leptons, and implied a mass formula that correctly reproduced the masses of the known mesons.
1970
Sheldon Lee Glashow, John Iliopoulos and Luciano Maiani predicted the charm quark that was subsequently found experimentally and shared a Nobel prize for their theoretical prediction.
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