Speaker
Description
Remarkable advances have been made in recent years with the theoretical description of electromagnetic properties of atomic nuclei, stimulated by a wealth of high-quality experimental data on short-lived radionuclides (see references [1-6]). In this context, nuclear charge radii are highly rewarding observables which serve as a sensitive probe of phenomena such as pairing, deformation, or shell closures, and thus represent intriguing experimental benchmarks for modern nuclear structure theory.
Density functional theory (DFT) has emerged as a powerful theoretical approach for the prediction of nuclear charge radii. In particular, the Fayans functional has been successful in predicting the odd-even staggering of charge radii along the calcium isotopic chain as well as the unexpectedly large charge radius of $^{52}$Ca [1, 7]. The same functional has been extended into the mid-mass regions for predictions of Ni [4], Cu [3], and Sn [8] charge radii, and has even been applied to Fm (Z=100)[9].
For cadmium (Z=48), DFT calculations utilizing the same Fayans functional have been successful in predicting the odd-even staggering in the charge radii of $^{100-130}$Cd [2], however, its description of mid-shell region tends to overestimate the slope and curvature of differential radii. Hence, a new Fayans functional was recently introduced which added an isovector component in its pairing functional [6, 10]. Measurements of the still undetermined charge radii of $^{98,99}$Cd down to the N=50 shell closure would thus represent powerful experimental benchmark for the the Fayans functional, especially with the addition of the isovector term.
In order to make such charge radii measurements, Collinear Laser Spectroscopy (CLS) has proven to be a highly effective tool for precise measurements of nuclear ground state properties of radionuclides such as the nuclear spin, electromagnetic moments, and charge radius. The Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) is a new experimental setup at ISOLDE which aims to improve the sensitivity of conventional CLS by conducting it in a high-energy (> 10 keV) multi-reflection time-of-flight (MR-ToF) device [11, 12]. This is a type of ion trap which utilizes two electrostatic mirrors to reflect ion bunches back and forth for several thousands of revolutions. Hence, the ion bunches can be probed by the laser multiple times per measurement cycle to obtain higher statistics than with conventional fluorescence-based CLS, which can study the ion bunch only once. The resulting improvement in sensitivity allows isotopes with yields as low as 5 ions per $\mu$C to become accessible.
In August of this year, MIRACLS had a successful beamtime measuring the charge radii of $^{98,99}$Cd as well as the electromagnetic moments for $^{99}$Cd. In this contribution, I will discuss the latest experimental results at MIRACLS for these cadmium measurements.
References:
[1] R. F. Garcia Ruiz, et al., Nat. Phys., 12, 594–598, 2016.
[2] M. Hammen, et al., PRL, 121:102501, 2018.
[3] R. P. de Groote, et al., Nat. Phys., 16, 620–624, 2020.
[4] S. Malbrunot-Ettenauer, et al. PRL, 128:022502, 2022.
[5] A. Koszorus, et al., Nat. Phys., 17, 439–443, 2021.
[6] J. Karthein, et al., Nat. Phys., 20, 1719–1725, 2024.
[7] A.J. Miller, et al., Nat. Phys. 15, 432–436, 2019.
[8] C. Gorges,et al., PRL, 122:192502, 2019.
[9] J. Warbinek, et al., Nature, 634, 1075–1079, 2024.
[10] S. J. Wang, et. al., Phys. Lett. B, 856:138867, 2024.
[11] Simon Sels et al NIMA B 463, 310–314, 2020.
[12] F.M. Maier et al. NIMA A 1048, 2023.
