Magnetic moments of 33Mg in the time-odd relativistic mean field approach

Nuclear magnetic moment is one of the most important physical observables. The precise measurement of nuclear magnetic moment and its understanding in microscopic way are quite a challenge in nuclear physics. The research team at Peking University, who has dedicated to the study of nuclear structure and astrophysics for the last decades, has applied the configuration-fixed deformation constrained RMF approach with time-odd component to investigate the ground-state properties of 33Mg and reproduce the data self-consistently without introducing any parameter. The study is reported in Issue 52 (October, 2009) of Science in China Series G: Physics, Mechanics & Astronomy. Recently the magnetic moment of 33Mg has become a hot topic due to the following reasons: 1) it is a neutron-rich nucleus close to the so-called "island of inversion"; 2) different spins and configurations for the ground state of 33Mg are assigned in a series of experiments. In order to remove the confusion, the spin and magnetic moment for the ground state in 33Mg have been directly measured by Yordanov et al with I=3/2 and =-0.7456(5)N, which becomes a test for various theoretical approaches.

In shell-model, the magnetic moment of the ground state in 33Mg can be reproduced only in the model space with 2p-2h configuration. With the assignment of configuration by Tripathi et al, the simple Additivity Rules can only account for half of the experimental magnetic moment.

As one of the microscopic self-consistent theories, the RMF theory has achieved great success in describing many nuclear phenomena. For odd-A nuclei, the odd nucleon breaks the time-reversal invariance, and time-odd fields give rise to the nuclear magnetic potential which together with the corresponding core polarization will provide the nuclear current and contribute to magnetic moments. In the paper by Li et al, the ground state properties of 33Mg including the binding energy and magnetic moment have been investigated self-consistently in axially deformed RMF approach with time-odd components of vector meson fields.

"The magnetic moment 0.913N is obtained with the effective electromagnetic current which well reproduces the data 0.7456N self-consistently without introducing any parameter, in contrast with the shell-model results -0.675N and -0.705N restricted to 2p-2h configuration using two different interactions designed specifically for the island of inversion." noted principal investigator Jie Meng, professor at Peking University.

The main conclusion reported by the investigators is that the ground state of 33Mg has been found to be prolate deformed, with both ground state energy and the magnetic moment well reproduced the experimental data self-consistently without introducing any parameter.

Apart from the core polarization and nuclear magnetic potential, the meson exchange current correction is also very important for the description of nuclear magnetic moment, in particular for the isovector magnetic moment. Investigations along this line are in progress.

Source: Science in China Press