Nuclear physics
Nuclear physics |
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Nuclear physics is the field of
Nuclear physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons.
Discoveries in nuclear physics have led to
History
The history of nuclear physics as a discipline distinct from
In the years that followed, radioactivity was extensively investigated, notably by
The 1903 Nobel Prize in Physics was awarded jointly to Becquerel, for his discovery and to Marie and Pierre Curie for their subsequent research into radioactivity. Rutherford was awarded the Nobel Prize in Chemistry in 1908 for his "investigations into the disintegration of the elements and the chemistry of radioactive substances".
In 1905, Albert Einstein formulated the idea of mass–energy equivalence. While the work on radioactivity by Becquerel and Marie Curie predates this, an explanation of the source of the energy of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the nucleons.
Rutherford discovers the nucleus
In 1906, Ernest Rutherford published "Retardation of the α Particle from Radium in passing through matter."[4] Hans Geiger expanded on this work in a communication to the Royal Society[5] with experiments he and Rutherford had done, passing alpha particles through air, aluminum foil and gold leaf. More work was published in 1909 by Geiger and Ernest Marsden,[6] and further greatly expanded work was published in 1910 by Geiger.[7] In 1911–1912 Rutherford went before the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now understand it.
Published in 1909,
Eddington and stellar nuclear fusion
Around 1920, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars.[17][18] At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen (see metallicity), had not yet been discovered.
Studies of nuclear spin
The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the California Institute of Technology in 1929. By 1925 it was known that protons and electrons each had a spin of ±+1⁄2. In the Rutherford model of nitrogen-14, 20 of the total 21 nuclear particles should have paired up to cancel each other's spin, and the final odd particle should have left the nucleus with a net spin of 1⁄2. Rasetti discovered, however, that nitrogen-14 had a spin of 1.
James Chadwick discovers the neutron
In 1932 Chadwick realized that radiation that had been observed by
With the discovery of the neutron, scientists could at last calculate what fraction of binding energy each nucleus had, by comparing the nuclear mass with that of the protons and neutrons which composed it. Differences between nuclear masses were calculated in this way. When nuclear reactions were measured, these were found to agree with Einstein's calculation of the equivalence of mass and energy to within 1% as of 1934.
Proca's equations of the massive vector boson field
Alexandru Proca was the first to develop and report the massive vector boson field equations and a theory of the mesonic field of nuclear forces. Proca's equations were known to Wolfgang Pauli[20] who mentioned the equations in his Nobel address, and they were also known to Yukawa, Wentzel, Taketani, Sakata, Kemmer, Heitler, and Fröhlich who appreciated the content of Proca's equations for developing a theory of the atomic nuclei in Nuclear Physics.[21][22][23][24][25]
Yukawa's meson postulated to bind nuclei
In 1935
With Yukawa's papers, the modern model of the atom was complete. The center of the atom contains a tight ball of neutrons and protons, which is held together by the strong nuclear force, unless it is too large. Unstable nuclei may undergo alpha decay, in which they emit an energetic helium nucleus, or beta decay, in which they eject an electron (or positron). After one of these decays the resultant nucleus may be left in an excited state, and in this case it decays to its ground state by emitting high-energy photons (gamma decay).
The study of the strong and weak nuclear forces (the latter explained by Enrico Fermi via Fermi's interaction in 1934) led physicists to collide nuclei and electrons at ever higher energies. This research became the science of particle physics, the crown jewel of which is the standard model of particle physics, which describes the strong, weak, and electromagnetic forces.
Modern nuclear physics
A heavy nucleus can contain hundreds of
Superimposed on this classical picture, however, are quantum-mechanical effects, which can be described using the nuclear shell model, developed in large part by Maria Goeppert Mayer[28] and J. Hans D. Jensen.[29] Nuclei with certain "magic" numbers of neutrons and protons are particularly stable, because their shells are filled.
Other more complicated models for the nucleus have also been proposed, such as the interacting boson model, in which pairs of neutrons and protons interact as bosons.
Ab initio methods try to solve the nuclear many-body problem from the ground up, starting from the nucleons and their interactions.[30]
Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high spin and excitation energy. Nuclei may also have extreme shapes (similar to that of Rugby balls or even pears) or extreme neutron-to-proton ratios. Experimenters can create such nuclei using artificially induced fusion or nucleon transfer reactions, employing ion beams from an accelerator. Beams with even higher energies can be used to create nuclei at very high temperatures, and there are signs that these experiments have produced a phase transition from normal nuclear matter to a new state, the quark–gluon plasma, in which the quarks mingle with one another, rather than being segregated in triplets as they are in neutrons and protons.
Nuclear decay
Eighty elements have at least one
The most stable nuclei fall within certain ranges or balances of composition of neutrons and protons: too few or too many neutrons (in relation to the number of protons) will cause it to decay. For example, in
In alpha decay, which typically occurs in the heaviest nuclei, the radioactive element decays by emitting a helium nucleus (2 protons and 2 neutrons), giving another element, plus helium-4. In many cases this process continues through several steps of this kind, including other types of decays (usually beta decay) until a stable element is formed.
In
Other more exotic decays are possible (see the first main article). For example, in internal conversion decay, the energy from an excited nucleus may eject one of the inner orbital electrons from the atom, in a process which produces high speed electrons but is not beta decay and (unlike beta decay) does not transmute one element to another.
Nuclear fusion
In
Nuclear fission
Nuclear fission is the reverse process to fusion. For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. It is therefore possible for energy to be released if a heavy nucleus breaks apart into two lighter ones.
The process of alpha decay is in essence a special type of spontaneous nuclear fission. It is a highly asymmetrical fission because the four particles which make up the alpha particle are especially tightly bound to each other, making production of this nucleus in fission particularly likely.
From several of the heaviest nuclei whose fission produces free neutrons, and which also easily absorb neutrons to initiate fission, a self-igniting type of neutron-initiated fission can be obtained, in a
For a neutron-initiated chain reaction to occur, there must be a critical mass of the relevant isotope present in a certain space under certain conditions. The conditions for the smallest critical mass require the conservation of the emitted neutrons and also their slowing or moderation so that there is a greater cross-section or probability of them initiating another fission. In two regions of Oklo, Gabon, Africa, natural nuclear fission reactors were active over 1.5 billion years ago.[32] Measurements of natural neutrino emission have demonstrated that around half of the heat emanating from the Earth's core results from radioactive decay. However, it is not known if any of this results from fission chain reactions.[33]
Production of "heavy" elements
According to the theory, as the Universe cooled after the Big Bang it eventually became possible for common subatomic particles as we know them (neutrons, protons and electrons) to exist. The most common particles created in the Big Bang which are still easily observable to us today were protons and electrons (in equal numbers). The protons would eventually form hydrogen atoms. Almost all the neutrons created in the Big Bang were absorbed into helium-4 in the first three minutes after the Big Bang, and this helium accounts for most of the helium in the universe today (see Big Bang nucleosynthesis).
Some relatively small quantities of elements beyond helium (lithium, beryllium, and perhaps some boron) were created in the Big Bang, as the protons and neutrons collided with each other, but all of the "heavier elements" (carbon, element number 6, and elements of greater atomic number) that we see today, were created inside stars during a series of fusion stages, such as the proton–proton chain, the CNO cycle and the triple-alpha process. Progressively heavier elements are created during the evolution of a star.
Energy is only released in fusion processes involving smaller atoms than iron because the binding energy per
See also
- Isomeric shift
- Neutron-degenerate matter
- Nuclear chemistry
- Nuclear matter
- Nuclear model
- Nuclear spectroscopy
- Nuclear structure
- Nucleonica, web driven nuclear science portal
- QCD matter
References
- ISBN 978-0-470-01999-3.
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- Thomson, Joseph John (1897). "Cathode Rays". Proceedings of the Royal Institution of Great Britain. XV: 419–432.
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- ^ H. Geiger and E. Marsden, PM, 25, 604 1913, citing, H. Geiger and E. Marsden, Roy. Soc. Proc. vol. LXXXII. p. 495 (1909), in, The Laws of Deflexion of α Particles Through Large Angles \\ H. Geiger and E. Marsden Archived 2019-05-01 at the Wayback Machine (1913), (published subsequently online by – physics.utah.edu (University of Utah)) Retrieved June 13, 2021 (p.1):"..In an earlier paper, however, we pointed out that α particles are sometimes turned through very large angles..."(p.2):"..Professor Rutherford has recently developed a theory to account for the scattering of α particles through these large angles, the assumption being that the deflexions are the result of an intimate encounter of an α particle with a single atom of the matter traversed. In this theory an atom is supposed to consist of a strong positive or negative central charge concentrated within a sphere of less than about 3 × 10–12 cm. radius, and surrounded by electricity of the opposite sigh distributed throughout the remainder of the atom of about 10−8 cm. radius..."
- ^ a b Radvanyi, Pierre (January–February 2011). "Physics and Radioactivity after the Discovery of Polonium and Radium" (electronic). Chemistry International. 33 (1). online: International Union of Pure and Applied Chemistry. Archived from the original on 9 July 2023. Retrieved 13 June 2021.
..Geiger and an English-New Zealand student, E. Marsden, to study their scattering through thin metallic foils. In 1909, the two physicists observe that some alpha-particles are scattered backwards by thin platinum or gold foils (Geiger 1909)...It takes Rutherford one and a half years to understand this result. In 1911, he concludes that the atom contains a very small 'nucleus'...
- ^ Rutherford F.R.S., E. (May 1911). "The Scattering of α and β Particles by Matter and the Structure of the Atom". Philosophical Magazine. 6. 21 May 1911: 669–688. Archived from the original on 12 February 2020. Retrieved 13 June 2021.
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- ^ "1911 John Ratcliffe and Ernest Rutherford (smoking) at the Cavendish Laboratory..." Fermilab. Archived from the original on 1 April 2021. Retrieved 13 June 2021."..that would become a classic technique of particle physics..."
- Florida State: Florida State University. Archivedfrom the original on 13 June 2021. Retrieved 13 June 2021. "experiment was conducted 1911"
- "CULTURE AND HISTORY FEATURE Rutherford, transmutation and the proton 8 May 2019 The events leading to Ernest Rutherford's discovery of the proton, published in 1919". CERN Courier. IOP Publishing. 8 May 2019. Archived from the original on 18 April 2021. Retrieved 13 June 2021."...1909...a couple of years later..."
- "This Month in Physics History: May, 1911: Rutherford and the Discovery of the Atomic Nucleus". APS News. 15 (5). May 2006. Archivedfrom the original on 13 June 2021. Retrieved 13 June 2021."..1909..published – 1911.."
- Anderson, Ashley. "Timeline". University of Alaska-Fairbanks. Archived from the original on 13 June 2021. Retrieved 13 June 2021. "1911 performed "
- 1911 discovers:
- Leonard, P. and Gehrels, N. (November 28, 2009) A History of Gamma-Ray Astronomy Including Related Discoveries Archived 2021-06-13 at the High Energy Astrophysics Science Archive Research Center(HEASARC), Retrieved 13 June 2021
- Rizvi, Eram – Quantum Mechanics and Particle Scattering Lecture 1 Archived 2021-06-13 at the Queen Mary University London: School of Physics and Astronomy – Particle Physics Research Centre, Retrieved 13 June 2021 "..by Rutherford.."
- Leonard, P. and Gehrels, N. (November 28, 2009) A History of Gamma-Ray Astronomy Including Related Discoveries Archived 2021-06-13 at the
- rutherford/biographical Archived 2023-06-03 at the Wayback Machine, Nobel Prize, "..In 1910, his investigations into the scattering of alpha rays and the nature of the inner structure of the atom which caused such scattering led to the postulation of his concept of the 'nucleus'..."
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..It is suggested that, in 1910, the 'plum pudding model' was suddenly overturned by Rutherford's experiment. In fact, Rutherford had already formulated the nuclear model of the atom before the experiment was carried out..
- ^ a b Jariskog, Cecilia (December 2008). "ANNIVERSARY The nucleus and more" (PDF). CERN Courrier. p. 21. Archived (PDF) from the original on 13 June 2021. Retrieved 13 June 2021.
.. in 1911, Rutherford writes: "I have been working recently on scattering of alpha and beta particles and have devised a new atom to explain the results..
- ^ a b c Godenko, Lyudmila. The Making of the Atomic Bomb (E-Book). cuny.manifoldapp.org CUNY's Manifold (City University of New York). Retrieved 13 June 2021.
The discovery for which Rutherford is most famous is that atoms have nuclei; ...had its beginnings in 1909...Geiger and Marsden published their anomalous result in July, 1909...The first public announcement of this new model of atomic structure seems to have been made on March 7, 1911, when Rutherford addressed the Manchester Literary and Philosophical Society;...
[permanent dead link] - San Jose University. Archived from the originalon 30 January 2020. Retrieved 14 June 2021.
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- ^ Not a typical example as it results in a "doubly magic" nucleus
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- ^ Biello, David (July 18, 2011). "Nuclear Fission Confirmed as Source of More than Half of Earth's Heat". Scientific American. Archived from the original on 25 January 2023. Retrieved 25 January 2023.
Bibliography
- General Chemistry by Linus Pauling (Dover 1970) ISBN 0-486-65622-5
- Introductory Nuclear Physics by Kenneth S. Krane (3rd edition, 1987) ISBN 978-0471805533[Undergraduate textbook]
- Theoretical Nuclear And Subnuclear Physics by John D. Walecka (2nd edition, 2004) ISBN 9812388982[Graduate textbook]
- Nuclear Physics in a Nutshell by Carlos A. Bertulani (Princeton Press 2007) ISBN 978-0-691-12505-3
External links
- Ernest Rutherford's biography at the American Institute of Physics Archived 2016-07-30 at the Wayback Machine
- American Physical Society Division of Nuclear Physics
- American Nuclear Society
- Annotated bibliography on nuclear physics from the Alsos Digital Library for Nuclear Issues
- Nuclear science wiki
- Nuclear Data Services – IAEA
- Nuclear Physics, BBC Radio 4 discussion with Jim Al-Khalili, John Gribbin and Catherine Sutton (In Our Time, Jan. 10, 2002)