Despite the discovery of the nucleus and great advances in quantum physics over the past century, a detailed understanding of complex nuclei has not yet been achieved. Today, the nuclear shell model is the accepted model for predicting nuclear properties, and modern predictions must be tested against theory. The g factors of nuclei are sensitive to the orbital occupation of nucleons. In some regions of the nuclear chart g(21+) values in even-even nuclei can be used to probe shell closures. Therefore, comparison between theoretical and experimental g factors are valuable. However, such states often have lifetimes in the picosecond range, making for challenging measurements. Two techniques, one utilising the transient field (TF) and the other the hyperfine field of recoiling ions in vacuum (RIV), have been used to make such measurements. While the two techniques have been very successful, the transient-field technique relies on an empirical parametrization with inherent uncertainty, while the recoil-in-vacuum technique can require modelling complex atomic interactions.

In this seminar the results of g(21+) measurements made using the TF technique in 26Mg and the stable even-even Ge and Se isotopes will be presented. Comparisons with shell-model calculations will be made, and insights into the validity of the transient-field parametrization in the region 28 ≤ Z ≤ 48 will be drawn. The RIV technique will be presented as a solution to the parametrization issue. The problem of understanding the complex atomic interactions will be discussed, as well as progress made towards a Monte-Carlo simulation of the atomic states, and the capability to model them and determine precise, absolute g factors.