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)

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In this work, we report on the results of feasibility studies for the planned T violation searches by determination of angular correlations in the o-Ps[right arrow]3[gamma] decay based on a test run of the J-PET detector.
The most precise measurements studied the angular correlation operators in the decay of orthopositronium states into three photons and determined mean values of final state operators odd under the CP and CPT conjugations, finding no violation signal at the sensitivity level of [10.sup.-3] [39,40].
In this paper long, medium, and short range studies (X-Ray Diffraction (XRD), Positron Annihilation Lifetime Spectroscopy (PALS), and Perturbed Angular Correlations, (PAC)) were successfully applied to characterize the zirconium minerals originated from Australia, South Africa, and United States of America.
Experimentally, authors studied levels energy with their half-lives, transition probabilities, decay schemes, multipole mixing ratios, internal conversion coefficients, angular correlations and nuclear orientation of [gamma]-rays [1-4].
* Novel Proton Detectors for Angular Correlations of UCN Decay
Two-particle angular correlations in [eta] and [phi] spaces were first studied by ACM Collaboration at ISR energies [47].
An identification of bond angles or local structure in an amorphous system, from the study of angular correlations of the diffracted intensity, is another attractive topic of research.
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:
Tumasyan et al., "Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC," Journal of High Energy Physics, vol.
Currently, the beta-neutrino asymmetry has the largest uncertainty (4%) of the neutron decay angular correlations. Without requiring polarimetry, this decay parameter can be used to measure [lambda]([g.sub.a]/[g.sub.v]), test Cabibbo-Kobayashi-Maskawa (CKM) unitarity, limit scalar and tensor currents, and search for Charged Vector Current (CVC) violation.
[2,4] and from electron-neutrino angular correlations in the decay of [.sup.33]Ar [5] is shown in Fig.
Invited contributors review the literature and report current research on using perturbed angular correlation (PAC) spectroscopy to study defects and diffusion at the atomic scale.

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