- Atomic physics
Atomic physics (or atom physics) is the field of
physicsthat studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and the processes by which these arrangements change. This includes ionsas well as neutral atoms and, unless otherwise stated, for the purposes of this discussion it should be assumed that the term "atom" includes ions.
The term "atomic physics" is often associated with
nuclear powerand nuclear bombs, due to the synonymous use of "atomic" and "nuclear" in standard English. However, physicists distinguish between atomic physics—which deals with the atom as a system comprising of a nucleus and electrons, and nuclear physics—which considers atomic nuclei alone.
As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of "
atomic, molecular, and optical physics". Physics research groups are usually so classified.
Atomic physics always considers atoms in isolation. Atomic models will consist of a single nucleus which may be surrounded by one or more bound electrons. It is not concerned with the formation of
molecules (although much of the physics is identical) nor does it examine atoms in a solid state as condensed matter. It is concerned with processes such as ionizationand excitation by photons or collisions with atomic particles.
While modelling atoms in isolation may not seem realistic, if one considers atoms in a
gasor plasma then the time-scales for atom-atom interactions are huge in comparison to the atomic processes that we are concerned with. This means that the individual atoms can be treated as if each were in isolation because for the vast majority of the time they are. By this consideration atomic physics provides the underlying theory in plasma physics and atmospheric physicseven though both deal with huge numbers of atoms.
Electrons form notional shells around the nucleus. These are naturally in a
ground statebut can be excitedby the absorption of energy from light ( photons), magnetic fields, or interaction with a colliding particle (typically other electrons). The excited electron may still be bound to the nucleusand should, after a certain period of time, decay back to the original ground state. The energy is released as a photon. Thereare strict selection rulesas to the electronic configurations that can be reached by excitation by light—however there are no such rules for excitation by collision processes.
An electron may be sufficiently excited so that it breaks free of the nucleus and is no longer part of the atom. The remaining system is an
ionand the atom is said to have been ionizedhaving been left in a charged state.
History and developments
The majority of fields in physics can be divided between theoretical work and experimental workand atomic physics is no exception. It is usually the case, but not always, that progress goesin alternate cycles from an experimental observation, through to a theoretical explanationfollowed by some predictions which may or may not be confirmed by experiment, and so on. Of course, the current state of technology at any given time can put limitations on what can be achieved experimentally and theoretically so it may take considerable time for theory to be refined.
Clearly the earliest steps towards atomic physics was the recognition that matter was composedof "atoms", in the modern sense of the basic unit of a
chemical element. This theory was developed by the British chemist and physicist John Daltonin the 18th century. At this stage, it wasn't clear what atoms were although they could be described and classified by their properties (in bulk) in a periodic table.
The true beginning of atomic physics is marked by the discovery of
spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom modeland to the birth of quantum mechanicsitself. In seeking to explain atomic spectra an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this yield a better overall description, i.e. the atomic orbital model, but it also provided a new theoretical basis for chemistry( quantum chemistry) and spectroscopy.
Second World War, both theoretical and experimental fields have advanced at a great pace. This can be attributed to progress in computing technology which has allowed bigger and more sophisticated models of atomic structure and associated collision processes. Similar technological advances in accelerators, detectors, magnetic field generation and lasers have greatly assisted experimental work.
Significant atomic physicists
; Pre quantum mechanics
Joseph von Fraunhofer
J.J. Thomson; Post quantum mechanics
* David Bates
Clinton Joseph Davisson
Charlotte Froese Fischer
* Harrie S. Massey
* Mike Seaton
John C. Slater
George Paget Thomson
* cite book|title=Physics of Atoms and Molecules|author=Bransden, BH|coauthors=Joachain, CJ
year=2002|publisher=Prentice Hall|edition=2nd Edition|id=ISBN 0-582-35692-X
* cite book|title=Atomic Physics|author=Foot, CJ|year=2004
publisher=Oxford University Press|id=ISBN 0-19-850696-1
* [http://plasma-gate.weizmann.ac.il/API.html Atomic Physics on the Internet]
* [http://jilawww.colorado.edu/research/atomic.html JILA (Atomic Physics)]
* [http://www.phy.ornl.gov ORNL Physics Division]
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