Scattering experiments

Scattering experiments (atoms and molecules)

Experiments in which a beam of incident electrons, atoms, or molecules is deflected by collisions with an atom or molecule. Such experiments provide tests of the theory of scattering as well as information about atomic and molecular forces. Scattering experiments can be designed to simulate conditions in planetary atmospheres, electrical discharges, gas lasers, fusion reactors, stars, and planetary nebulae. See Electrical conduction in gases, Gas discharge, Laser, Nuclear fusion

In general, in any type of collision, scattering occurs, which causes the direction of relative motion of the two systems to be rotated to a new direction after the collision. More than two systems may also result from such an impact. A complete description of a collision event requires measurement of the directions, speeds, and internal states of all the products. See Collision (physics)

There are two basic types of scattering experiments. The simpler involves passing a collimated beam of particles (electrons, atoms, molecules, or ions) through a dilute target gas (in a cell or a jet) and measuring the fraction of incident particles that are deflected into a certain angle relative to the incident beam direction. In the second method, a collimated beam of particles intersects a second beam. The scattering events are usually registered by measuring the deflection or internal-state change of the beam particles. See Molecular beams

Scattering in a particular type of collision is specified in terms of a differential cross section. The probability that, in a particular type of collision, the direction of motion of the electron is turned through a specified scattering angle into a specified solid angle is proportional to the corresponding differential scattering cross section. Collision cross sections can be measured with appropriately designed experimental apparatus. Depending on the type of collision process, that apparatus may measure the scattering angle, energy, charge, or mass of the scattered systems.

For the simplest case, the scattering of a beam of structureless particles of specified mass and speed by a structureless scattering center, the differential cross section may be calculated exactly by using the quantum theory. In the special case where the Coulomb force fully describes the interaction, both the quantum and classical theory give the same exact value for the differential cross section at all values of the scattering angle.

For scattering of systems with internal structure (for example, molecules, and their ions), no exact theoretical calculation of the cross section is possible. Methods of approximation specific to different types of collisions have been developed. The power of modern high-speed computers has greatly increased their scope and effectiveness, with scattering experiments serving as benchmarks. See Atomic structure and spectra


Scattering experiments (nuclei)

Experiments in which beams of particles such as electrons, nucleons, alpha particles and other atomic nuclei, and mesons are deflected by elastic collisions with atomic nuclei. Much is learned from such experiments about the nature of the scattered particle, the scattering center, and the forces acting between them. Scattering experiments, made possible by the construction of high-energy particle accelerators and the development of specialized techniques for detecting the scattered particles, are one of the main sources of information regarding the structure of matter. See Nuclear structure, Particle accelerator, Particle detector, Scattering matrix

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
X-ray scattering experiments are performed at Beamline 1W2A of Beijing Synchrotron Radiation Facility (Beijing, China).
It would be welcome if the emergence of the Compton wavelength, a more intuitive grasp of electron spin, and the apparent pointlikeness of the electron in high-energy scattering experiments could be understood, possibly in extensions of the model incorporating quantum effects from the outset and doing justice to L.
The 14 papers consider such topics as Swiss light sources: the next 20 years, accelerator projects in Korea: current status and perspectives, challenges and opportunities of high-intensity X/gamma photon beams for nuclear photonics and photon-photon scattering experiments, advances and perspectives of synchrotron-based techniques for cultural heritage, and energy catalysis research with advanced X-ray techniques in the Shanghai Synchrotron Radiation Facility: present and future challenges.
Using results from simulations and X-ray scattering experiments, scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and at the University of California, Berkeley, found the electrons in vanadium dioxide are able to conduct electricity without conducting heat at a rate of thermal conductivity which was "ten times smaller than what would be expected from the Wiedemann-Franz Law."
Notably, the approach does not require the exact knowledge of the field impinging on the obstacles but, rather, the knowledge of scattered fields under a sufficiently large number of different scattering experiments. In the case of PEC obstacles, the approach takes advantage of the fact that the induced currents are null inside the target except for the boundary of the target [23].
The Compact Dynamic Beamstop (CDBS) design is simple, compact, easily commercialized, customizable for a wide variety of X-ray scattering experiments and unique in its capabilities to provide information about X-ray beams in real time without interfering with the collection of data on precious samples.
Examination of Equation 4 leads to several observations about Rayleigh scattering experiments. First, decreasing the incident light wavelength greatly increases the scattering intensity.
Experienced researchers introduce students to the capabilities and the limits of conducting X-ray scattering experiments using nanobeams--X-ray beams focused to sub-micron spot size.
Laser Light Scattering Experiments. It has been reported [23, 38] that addition of ionic surfactants influences the molecular structure of the polymer.
The inelastic neutron scattering experiments performed on the above two materials show a "central peak", that is, a peak at [omega] = 0 in the constant q-scan for the dynamical structure function for both of them [13-16].
Scattering experiments are used as a primary tool for investigating the structure of physical objects.