angular correlations

Angular correlations

An experimental technique that involves measuring the manner in which the likelihood of occurrence (or intensity or cross section) of a particular decay or collision process depends on the directions of two or more radiations associated with the process. Traditionally, these radiations are emissions from the decay or collision process. However, a variant on this technique in which the angular correlations are between an incident and emitted beam of radiation has been widely used; this variant is known as angular distributions.

The fundamental reason for performing such measurements, rather than just scrutinizing a single radiation in a particular direction or measuring the total intensity for a process, is that the angular correlation or angular distribution measurement provides much more information on both the decay or collision process and on the structure and properties of the emitter of the radiation. The technique is used to study a variety of decay and collision processes in atomic and molecular physics, condensed-matter (solid-state) and surface physics, and nuclear and particle physics.

The principal use of this technique in nuclear physics has been to determine the angular momentum, or spin, and parity of excited nuclear states which are radioactive, that is, decay spontaneously, by measuring in coincidence the radiation in specific directions from two successive transitions in the radioactive cascade. The measurements are generally of coincidences between gamma rays, but coincidences between gamma rays and electrons (beta particles) are also used. The form of the angular correlation, the measured intensity as a function of the angle between the two radiations, gives the information about the intermediate excited state in the cascade. See Radioactivity

In atomic and molecular collisions as well as in nuclear and particle collisions, this technique is employed as a means of completely specifying the dynamics of the collision, with the added proviso that the energies of the emitted radiations are also to be measured. Wide use has been made of angular correlations in the impact ionization of atoms by electrons where the directions of both the scattered electron and the ejected electron are measured. See Atomic structure and spectra, Scattering experiments (atoms and molecules)

angular correlations

[′aŋ·gyə·lər ‚kär·ə′lā·shənz]
(nuclear physics)
A technique of nuclear experimentation for determining spins of nuclear states, the angular momentum mixtures of incoming or outgoing particles, and the multipole mixtures of emitted gamma rays, by measuring the dependence of the intensity or the cross section of a nuclear reaction on the directions of two or more radiations.
References in periodicals archive ?
The topics include impurities in magnetic materials, whether PAC measurements can be used to investigate defects in nano-structures, the volume and surface properties of TiO2 nanomaterials studied by 44Ti(EC)44Sc time differential perturbed angular correlations, and implanted impurities in wide band gap semiconductors.
Novel Proton Detectors for Angular Correlations of UCN Decay
Kurylov, California Institute of Technology 11:35-11:55 Determination of the Electron-antineutrino Angular Correlation Coefficient [a.
It is well-known that in the tree approximation (neglecting recoil corrections and electron/proton polarization) the neutron decay rate [13] can be written in terms of the angular correlations coefficients a, A, B and D:
Currently, the beta-neutrino asymmetry has the largest uncertainty (4%) of the neutron decay angular correlations.
2,4] and from electron-neutrino angular correlations in the decay of [.

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