Research Activities



Magnetic Moments

Measurements of magnetic moments are valuable tools in nuclear structure studies since, due to the big differences between the g factors of protons and neutrons, they are sensitive to single nucleon contributions to wave functions and their interplay with collective degrees of freedom. Interesting measurements can be performed in nuclei near closed shells, nuclei where the interplay between collective and single nucleon degrees of freedom is strong, high spin states of nuclei where the back-bending phenomenon occurs, and nuclei close to the drip lines where new phenomena are apparent, as the disappearing of magic numbers and the appearing of new ones. Most of the above states are short lived and their measurement should be accomplished through special techniques.

In general nuclear magnetic moments can be measured through their interactions with magnetic fields. In order to achieve the appropriate precision, hyperfine fields obtained through interactions between nuclei and their own atomic electrons, or the electrons in the solids, which they transverse must rather be used instead of the laboratory fields.

In particular, the magnetic hyperfine interaction, between a moving ion and the ferromagnetic environment in which it moves (transient magnetic fields), has been the subject of many studies in the borders of atomic and nuclear physics, while its application to magnetic moment measurements has produced numerous valuable results. The main features of a typical experimental set up are shown in the figure.

In most experiments, the state of interest is created preferentially by Coulomb excitation (of the beam or the target nuclei) or heavy ion fusion reactions. The excited ions recoil through a thin ferromagnetic material and stop in a thick backing where they are not subject to any further hyperfine interactions. Four gamma detectors are located at an angle theta, where the slope in the angular distribution of the decay gamma radiation is maximum. The ferromagnet is polarized either up or down by a small magnetic field and the gamma counting rate is recorded as a function of field direction. An effect, ε, is determined and finally the rotation of the magnetic moment which is manifested through the rotation of the distribution.

Where ε is the effect, S(θ) the slope of the distribution and Δθ  the rotation of the distribution and thus the rotation of the magnetic moment. The rotation is connected with the applied transient field, and the g-factor of the state through the following relation:

The transient field is given through parametrizations as a function of the ion velocity and the magnetization of the ferromagnetic material. Details of the technique and the field origin as well as its parametrization can be found in the article by Benczer-Koller, Hass and Sak in Ann. Rev. Nucl. Part. Sci. 30 (1980) 53.

One of the members of the NPL was specialized to such measurements and a series of articles can be found in A. Pakou's CV.




Last update: March 7, 2016