Are fundamental his researches on the radioactive phenomena, effected from 1897 to 1907
together with J.J. Thomson and F.Soddy, to determine the laws of a and b decay of the radioelements
of the three natural families (the ones of uranium-radium, of thorium and of
actinium).
In each series the founder, that is the element with the most long mean life ( some
billions of years ), decaying is transforming into the following radioelement, and so away
across all the consecutive unstable elements, until is produced a stable element (an
isotope of lead ).
His principal discovery concerns the atomic nucleus.
In 1911 Rutherford, after two years of researches together with
Geiger and Marsden, bombarding some thin gold layers with a particles
and studying the angular distribution of the a particles that
were scattered in all the directions, realized the impossibility to accept the atomic
model proposed in 1902 by J.J. Thomson, who supposed the electrons are dispersed in a
sphere with a positive electric charge uniformly distributed and equal to the negative one
of electrons, in such a mode that were kept electric neutrality.
The experimental data were instead compatible with the existence of a nucleous with a
positive electric charge and containing nearly whole the mass of an atom, since the events
relating to the scattering of particles at great angles or, although with a small
frequency, backwards, were only compatible with a massive nucleus having a positive
electric charge .
Rutherford enunciated therefore the discovery of the atomic nucleus, giving a decisive
impulse to the development of atomic physics.
It is owing besides to Rutherford to have produced the first artificial nuclear reaction.
In fact, in 1919, bombarding with a particle a target
containing nitrogen, he got as reaction products an isotope of the oxygen and hydrogen
nuclei (protons), of which he could measure kinetic energy. In 1908 he was conferred the
Nobel prize for the chemistry.
He was a pupil of J.J. Thomson and Rutherford.
In 1913 he elaborated the first theory of the atomic structure, founding on Rutherford's
atomic model and applying to the most simple atom, the one of hydrogen, the laws of
classical mechanics and some postulations that held account of the quantization of energy
and angular momentum of the only electron orbiting about the nucleus (a proton),
positively charged.
The atomic model that was builded up, which is known as Bohr-Rutherford's model, allowed
to develope an elementary atomic theory, that represented the first important step toward
the construction of atomic physics.
He founded the Copenaghen physics school, in which are formed in '20 years the most
illustrious exponents of the European atomic physics.
In nuclear physics he introduced the drop model of the atomic nucleus, which had a
fundamental importance for studying the fission of uranium and the one of plutonium
by slow neutrons.
He was given the Nobel prize in 1922.
His hypothesis ( 1924 ) of the wave-like behaviour of elementary particles, that gave
impulse to the creation of Schroedinger's quantum mechanics (that is even known as wave
mechanics), was suggested by analogy with Einstein's wave-particle-like dualism (the
theory of photons, 1905 ),introduced to explain the photoelectric effect.
De Broglie thought that, by analogy with electromagnetic radiation, that in the
interaction with the bodies of microcosm ( atoms and particles), shows particle-like
properties, because photons ( packets of electromagnetic energy) are involved as if they
were really material particles, so even for bodies of microcosm it was possible to
evidence
wave-like properties, and that therefore to any particle having a linear momentum MV, had to be associated a probability wave with the length l = h/( MV ), where h is universal Planck's constant that characterizes the physical
phenomena of microcosm.
De Broglie's hypothesis was verified experimentally (1927 ) by Davisson and Thomson, that
showed by means of diffraction experiments the wave-like properties of electrons,
getting some photos of diffraction rings much similar to the ones produced by Laue and
Bragg, in the first tens years of XX century,by X-rays, that are electromagnetic
waves.
He was conferred the Nobel prize in 1929.
After the degree was a Bohr's student at the Copenhagen school.
In 1925, independently from Schroedinger, created quantum mechanics, introducing the
matrix formalism.
It is famous his uncertainty principle, enunciated in 1927 as a fundamental postulate for
studying the physical phenomena of microcosm.
He was one of the founders of quantum electrodynamics.
Are fundamental his researches in the quantum field theory and in the physics of
elementary particles.
He was conferred the Nobel prize in 1932.
In 1925, independently from Heisenberg, he created quantum mechanics, introducing as a
fundamental equation his wave equation, whose solution is the wave function.
Schroedinger's equation,that is even said the probability wave equation, describing an
atom as a probability cloud, allows to calculate the probability to find electron in a
point of assigned coordinates referred to nucleus.
In 1933 he was conferred the Nobel prize together with P.A.M. Dirac.
After the publication of Heisenberg and Schroedinger's works, he furnished in 1928 a
relativistic version of the wave equation, that produced several fundamental results in
the physics of elementary particles with spin 1/2 ( electron, muon, neutrino, proton ),
since it implicates the existence of antiparticles ( positron, antimuon, antineutrino,
antiproton ).
Positron was discovered in 1932 by Anderson in the particle showers of cosmic radiation.
The relativistic wave equation is fundamental for the development of quantum
electrodynamics, of which Dirac is considered one of the founders.
He was conferred the Nobel prize in 1933 together with Schroedinger.
He is an extraordinary example of both theoretical and experimental physicist .
He effected researches of fundamental importance in all the sectors of physics, bringing
contributions whose ingeniousness is recognized by the whole international science
community.
After having worked with some of the most illustrious physicists of the XX century, at
Gottinga and Leyden, and having been appointed academician of Italy when he was only
27 years old, from 1923 to 1938, the year when he emigrated in the U.S.A., he brought
fundamental contributions to the quantum statistics of elementary particles with a
half-odd spin, denominated fermions in honor of him,to the theory of weak forces (1934 ), known even as Fermi's forces, that determine the b decay, and to production of many artificial radioactive isotopes by bombardment of atomic nuclei by slow neutrons.
His researches about neutrons, effected at the Rome university
(1934-1938 ), were the starting point for the discovery of nuclear fission of uranium by
Hahn and Strassman ( 1939 ).
In U.S.A. he realized and tested ( 1942 ), within the Manhattan project, the first nuclear
reactor (the so-called atomic pile), on which was based the realization of the first
nuclear bomb.
In the post-war period, passed initially at the university of Chicago,
he devoted himself primarily to some researches in high energy physics, studying cosmic
radiation and using the first particle accelerators,derived from the Lawrence
cyclotron, for the study of collisions of pions against nucleons, with the aid of the
first electronic computers.
In 1938 he was conferred the Nobel prize for his researches on neutrons.
His most important discovery is the exclusion principle (1925).
In 1925, following the creation of quantum mechanics by Heisenberg and Schroedinger, he
studied atomic structure as it was described by the new mechanics, realizing that, to be
able to represent the energetic levels of atoms coherently with the experimental data
furnished by optical and X-ray atomic spectra , it was needful to admit that two
atomic electrons cannot be in the same quantum state, individuated by four quantum
numbers: one connected with energy, two with orbital angular momentum and the remainder
with the intrinsic angular momentum (spin).
As a particular case, if two electrons have three quantum numbers
equals each other, their spins must be oriented in opposite directions.
His principle, that is a law of nature which must be applied to all the elementary particles with an
half-odd spin, is fundamental to explain not only the atomic structure of chemical
elements, but even the behaviour of any quantum system, whose particles (fermions) obey to
the Fermi-Dirac's statistics.
It is needful in fact to explain the electric conductibility of metals.
His ingeniousness as a theoretical physicist, permitted him to foresee in 1931 the
existence of neutrino,a particle with no mass neither electric charge, and to explain the
apparent violation of the energy conservation principle,that was evidenced measuring
the strange energetic distribution of electrons in b decay
phenomena.
Starting from his hypothesis of existence of neutrino, Enrico Fermi built his theory of
weak forces ( 1934 ).
Neutrinos, difficult to be detected because of their zero charge and their zero
mass,that currently, according to the most recent researches, it is thought to be very
small, are able to cross the whole Earth without interact, and have a fundamental role in
the controlling the speed of reactions of thermonuclear fusion that happen in the
Sun and in all the other stars.
Neutrino has been observed for the first time by Cowan and Reines, in 1956, studying
the weak interactions induced by neutrinos produced in nuclear reactors as a
consequence of the radioactive decay of fission fragments.
Pauli, which is considered one of the founders of the quantum electrodynamics, was given
the Nobel prize in 1945.
He is considered, after Enrico Fermi, one of the most illustrious nuclear physicists.
Toward the end of the '30 years he studied the application of quantum mechanics to
the atomic nucleus, discovering fundamental theorems concerning any space-time symmetries
of nuclear forces, that can be applied even to other sectors of physics, as the physics of
elementary particles.
The theorem of the temporal invariance establishes that physical phenomena of
microcosm are evolving in the same way when time is reversed.
That is the temporal reversibility at a microscopic level, that is applicable to only
three of four universal interactions.
In the particular case of electromagnetic interactions, the validity of Wigner's
theorem has been verified experimentally ( 1964 ) by the physicist Antonino Zichichi.
The contributions of Wigner to study of nuclear structure have a fundamental importance.
He worked actively with Enrico Fermi within the Manhattan project for the construction of
the first nuclear bomb.
In 1963 he was conferred the Nobel prize together with Maria Goeppert-Mayer and Hans J D.
Jensen.
Their researches concerned the improvement of quantum electrodynamics, introduced in
the last twenties by Dirac, Heisenberg and Pauli, that applied the principles of quantum
mechanics to the interactions between charged elementary particles and the electromagnetic
field.
The original theory introduced several drawbacks deriving from not having considered the
interactions of charged particles (electrons, positrons, muons, protons, etc...) with all
the virtual particle-antiparticle pairs that characterize the vacuum state of
quantum fields (the so-called polarization of vacuum).
Because of such a motive the calculations gave infinite contributions, that weren't
acceptable physically.
Tomonaga, Schwinger and Feynman elaborated, independently each from the others, some
particular methods of renormalization, so that quantum electrodynamics became one of the
most accurate theories that never have been developed.
The results of his theory were brightly confirmed by experimental data (the discovery in
1947 of Lamb's shift for the spectral line of the hydrogen atom), connected with virtual
physics, that describes the fluctuations of the vacuum state of quantum fields.
The calculation methods used to improve Q.E.D. (Quantum-Electro-Dynamics ) have been
subsequently used in the standard model, in the electro-weak theory (the unified theory of
electromagnetic and weak forces ), and in the quantum chromodynamics ( Q.C.D.-
Quantum-Chromo- Dynamics ), that studies the strong interactions among quarks,
inside hadrons.
They were conferred the Nobel prize in 1965.
