Speaker
Description
Electromagnetic transition rates and multipole moments are crucial observables for understanding and interpreting nuclear structure. While $E2$ transitions tend to be dominant among the low-excitation states of broad ranges of nuclei, particularly as collectivity emerges, and the magnetic moment is sensitive to the structure of an individual state, giving a measure of how the nucleus is carrying its angular momentum, higher-order moments are also important despite data being relatively rare. One example is the unique $E6$ transition in $^{53}$Fe [1] where it was found that the effective charges appropriate for higher-multipolarity $E4$ and $E6$ transitions differ from those applicable to $E2$. It can be said that the higher-multipolarity electric (magnetic) transitions help reveal the physics hidden in the effective charges ($g$ factors).
The data on magnetic octupole moments, which are fairly rare, have been compiled recently by Bofos and Mertzimekis [2]. It will be shown that the $M3$ magnetic octupole moment, in most of the cases that have been measured, can be estimated with considerable accuracy from the measured magnetic dipole ($M1$) moment. The level of agreement is a surprise, given that the core-polarization mechanism associated with the effective $g$ factors in the $M1$ operator is not expected to be applicable for the $M3$ operator.
Implications and possible explanations, along with some strategies for further investigation, will be discussed. For example, high-precision laser spectroscopy could add to the $M3$ moment data base [3,4] and it can be anticipated that a renaissance in muonic-atom x-ray spectroscopy [5] will yield new data on higher-order nuclear moments.
References
[1] T. Palazzo et al., Phys. Rev. Lett. 130 (2023) 12203.
[2] S. Bofos, T.J. Mertzimekis, Atomic Data and Nucl. Data Tables 159 (2024) 101672.
[3] V. Gerginov, A. Derevianko and C.E. Tanner, Phys. Rev. Lett. 91 (2003) 072501.
[4] R.P. de Groote et al., Phys. Lett. B 827 (2022) 136930.
[5] R.J. Powers et al., Phys. Rev. Lett. 34 (1975) 492.