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nuclear physics,study of the components, structure, and behavior of the nucleusnucleus,
in physics, the extremely dense central core of an atom. The Nature of the Nucleus
Atomic nuclei are composed of two types of particles, protons and neutrons, which are collectively known as nucleons.
..... Click the link for more information. of the atom. It is especially concerned with the nature of matter and with nuclear energynuclear energy,
the energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity. In these processes a small amount of mass is converted to energy according to the relationship E = mc2, where E is energy, m
..... Click the link for more information. .
The discipline involving the structure of atomic nuclei and their interactions with each other, with their constituent particles, and with the whole spectrum of elementary particles that is provided by very large accelerators. The nuclear domain occupies a central position between the atomic range of forces and sizes and those of elementary-particle physics, characteristically within the nucleons themselves. As the only system in which all the known natural forces can be studied simultaneously, it provides a natural laboratory for the testing and extending of many fundamental symmetries and laws of nature. Containing a reasonably large, yet manageable number of strongly interacting components, the nucleus also occupies a central position in the universal many-body problem of physics. See Atomic nucleus, Atomic structure and spectra, Elementary particle, Symmetry laws (physics)
Nuclear physics is unique in the extent to which it merges the most fundamental and the most applied topics. Its instrumentation has found broad applicability throughout science, technology, and medicine; nuclear engineering and nuclear medicine are two very important areas of applied specialization.
Nuclear chemistry, certain aspects of condensed matter and materials science, and nuclear physics together constitute the broad field of nuclear science; outside the United States and Canada elementary particle physics is frequently included in this more general classification. See Analog states, Fundamental interactions, Isotope, Nuclear fission, Nuclear fusion, Nuclear isomerism, Nuclear moments, Nuclear reaction, Nuclear spectra, Nuclear structure, Particle accelerator, Particle detector, Radioactivity, Scattering experiments (nuclei), Weak nuclear interactions
a branch of physics that studies the structure of the atomic nucleus, the processes of radioactive decay, and the mechanism of nuclear reactions. The meaning of the term is frequently expanded to include the physics of elementary particles as well. Sometimes areas of research that have become independent branches of technology, such as accelerator technology and nuclear power industry, continue to be considered as branches of nuclear physics. Historically, nuclear physics came into being even before the establishment of the existence of the atomic nucleus. The age of nuclear physics is considered to begin with the discovery of radioactivity.
There is no universally recognized division of modern nuclear physics into narrower fields and areas. A distinction is usually made between low-, medium-, and high-energy nuclear physics. Among the problems studied by low-energy nuclear physics are the structure of the nucleus, the radioactive decay of nuclei, and nuclear reactions produced by particles with energies of up to 200 megaelectron volts (MeV). Energies of 200 MeV to 1 GeV are considered to be medium, while those above 1 GeV are considered to be high. This demarcation is to a considerable extent arbitrary, especially the division into medium and high energies, and came about in connection with the development of accelerator technology. Nuclear structure is studied in contemporary nuclear physics by means of high-energy particles, and the fundamental properties of elementary particles are established through the study of the radioactive decay of nuclei.
An extensive area of low-energy nuclear physics is neutron physics, which includes the study of the interaction of slow neutrons with matter, as well as the study of nuclear reactions influenced by neutrons (neutron spectroscopy). A relatively new area of nuclear physics is the study of nuclear reactions involving multiply charged ions. Such reactions are used to find new heavy nuclei and to study the mechanism of the interaction of complex nuclei with one another. The study of the interaction of nuclei with electrons and photons is a separate branch of nuclear physics. All the branches of nuclear physics are closely intertwined and are linked by common goals.
There is a clear division between experiment and theory in nuclear physics, as in all of modern physics. The experimental means of nuclear physics are diverse and technically complex. The principal tools are (1) accelerators, which are used to increase the energy of charged particles, ranging from electrons to multiply charged ions, (2) nuclear reactors, which act as intense neutron sources, and (3) nuclear radiation detectors, which register the products of nuclear reactions. The modern nuclear experiment typically involves the simultaneous registration of several particles emitted in a single nuclear collision and the use of high-intensity beams of accelerated charged particles or neutrons, which makes it possible to study rare nuclear processes and phenomena. The multiplicity of data acquired in a single experiment necessitates the use of computers, which are directly tied into the recording equipment. The complexity and tediousness of a single experiment have made it feasible only for a large group of specialists.
Theoretical nuclear physics is characterized by the necessity of drawing upon the apparatus of various branches of theoretical physics, including classical electrodynamics, the theory of continuous media, quantum mechanics, statistical mechanics, and quantum field theory. The central problem of theoretical nuclear physics is the quantum problem of the motion of many bodies that strongly interact with one another. New areas of theoretical physics—for example, in the theory of superconductivity and in the theory of the chemical reaction—have evolved out of the theory of the nucleus and elementary particles; these new areas have subsequently found application in other branches of physics and stimulated new mathematical research (the inverse problem of the theory of scattering and its application to the solution of nonlinear partial differential equations). The development of theoretical and experimental nuclear research is interdependent. The problems facing nuclear physics are highly complex, and only in a few cases can they be solved in a purely theoretical or empirical way. Nuclear physics has considerably influenced the development of a number of other areas of physics, particularly astrophysics and solid-state physics, as well as a number of other sciences, such as chemistry, biology, and biophysics.
The practical applications of nuclear physics in modern society are enormous and unbelievably varied, ranging from nuclear weapons and the production of nuclear power to diagnosis and treatment in medicine. At the same time (and this is a feature unique to nuclear physics), it remains a fundamental science, where we can expect new advances to reveal the deep properties of the structure of matter and to lead to the discovery of new general laws of nature.
I. S. SHAPIRO
nuclear physics[′nü·klē·ər ′fiz·iks]