Speaker
Description
Following the N=28 shell closure, a pronounced change in the slope of the charge radii, often referred to as a "kink", has been observed in neutron-rich calcium isotopes [1,2]. However, the exact amplitude of this kink and the underlying reasons for this phenomenon remain unclear. Theoretical predictions suggest that several factors could contribute to this behaviour, including the presence of large nuclear deformations or significant radial extensions of the nuclear density distribution. To address these questions and explore the origins of the observed kink, we aim to determine the difference in the distribution of magnetisation for 47,48,49K by measuring their differential hyperfine anomalies (also known as Bohr-Weisskopf effect. To achieve this, we set out to measure precise magnetic dipole moments and hyperfine structure constants at the VITO beam line.
In October 2025, we performed the first part of these studies: we measured precisely magnetic moments of 47-49K using beta-NMR at VITO in solid (KCl) and liquid (EMIM-DCA ionic liquid) samples, thus reaching ppm precision [3]. In this contribution I will present the measurement principle, the upgraded experimental setup, the analysis of the collected data, and preliminary values of differential hyperfine anomaly between the isotopes. I will also mention how we aim to determine the hyperfine structure constants with improved precision. Finally, I will present our magnetic moment calculations using DFT with angular momentum symmetry restoration [4,5].
References:
[1] A. Koszorus, X. Yang, W. Jiang, S. Novario, S. Bai, J. Billowes, C. Binnersley, M. Bissell, T. E. Cocolios, B. Cooper, et al., Nature Physics 17, 439(2021).
[2] R. Garcia Ruiz, M. Bissell, K. Blaum, A. Ekstrom, N. Frommgen, G. Hagen, M. Hammen, K. Hebeler, J. Holt, G. Jansen, et al., Nature Physics 12, 594(2016).
[3] R. D. Harding et al., Phys. Rev. X 10 (2020) 041061.
[4] P.L. Sassarini et al., J. Phys G 49 (2022) 11LT01.
[5] J Dobaczewski et al., J. Phys. G: Nucl. Part. Phys. 48 (2021) 102001.