Magnetic moments: Study of the interplay between single-particle and collective excitations
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NUCLEI Theory
Magnetic Moments: Study of the Interplay between Single-Particle and Collective Excitations* N. Benczer-Koller1)** , G. J. Kumbartzki1), P. Boutachkov1), A. Escuderos1), Y. Y. Sharon1), L. Zamick1), E. A. Stefanova1), 2) , S. J. Q. Robinson3) , and V. Werner4) Received October 31, 2006
Abstract—Both theoretical descriptions of nuclei and experimental techniques for measuring magnetic moments have become very sophisticated. Yet, in general, good agreement between calculations and measurements still eludes us. Highlights are presented of new measurements of g factors of mixed70 symmetry states in 92,94 Zr, of the 4+ Ge, and of the 2+ 1 state in 1 states in some S and Ar isotopes. PACS numbers: 21.10.Ky, 21.60.Cs, 21.60.Ev, 27.30.+t, 27.40.+z, 27.50.+e, 27.60.+j DOI: 10.1134/S1063778807080029
1. INTRODUCTION
2. EXPERIMENTAL TECHNIQUE
The interplay between single-particle and collective excitations is very important in the lighter nuclei as well as in heavier ones. The measurement of magnetic moments of nuclear states allows for the establishment of constraints on the theoretical description of these states. In particular, the fact that singleparticle neutrons and protons have different magnetic moments, both in sign and magnitude, helps determine the microscopic structure of these states. A realistic description is, of course, more complex, and the interplay between collective and single-particle excitations results in magnetic moments that lie somewhere in between these two model extremes. Therefore, it becomes important for the experimental data to be as precise as possible so as to select among possible theoretical models.
Recently, new techniques have been developed to take advantage of the radioactive beams that are slowly becoming available. These techniques make use of the transient field that is felt by swift nuclei traversing ferromagnetic materials [1]. The nuclei of interest are usually, but not always, excited by Coulomb excitation. The exceptions involve cases where α or other nucleon transfer reactions occur. In recent experiments, projectiles have been excited in inverse kinematics, resulting in excited probe nuclei with relatively large velocities [2]. This technique exploits the facts that the transient field is higher for high-velocity ions and that the interacting target ions are focused by the kinematics in the forward direction, where they can be easily detected, thus increasing the effectiveness of the method. The technique has been described at length in several papers over the last few years [2–7]. A schematic layout of the experimental setup used in the inverse kinematics geometry experiments is shown in Fig. 1.
In this presentation, three examples will be displayed that show the effectiveness of magnetic moments when microscopic information on specific states’ wave functions is desired. The recent measurements in 92,94 Zr mixed-symmetry states, in N = 38 isotones, and in the A = 38, 40 isotopes of Ar and S will be discussed. ∗
The text was submitted by the authors in English. De
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