Electromagnetic moments and radii near N $=$32,34

On behalf of the COLLAPS and CRIS collaborations at ISOLDE-CERN. \\Nuclei in the neighborhood of calcium isotopes play a key role in the development of many-body methods and provide an important test for current descriptions of the nuclear force. The properties of stable nuclei in the vicinity of the two naturally occurring doubly-magic calcium ($Z=$20) isotopes, $^{\mathrm{40}}$Ca ($N=$20) and $^{\mathrm{48}}$Ca ($N=$28), have been extensively studied, both experimentally and theoretically. Recently, special attention has been given to the evolution of nuclear structure in exotic neutron-rich isotopes beyond $N=$28, where evidence of doubly-magic features have been reported at $N=$32 [1] and $N=$34 [2]. This contribution presents the latest results obtained with laser spectroscopy in the region. Measurements of the hyperfine structure spectra and isotope shifts for the potassium ($Z=$19) and calcium ($Z=$20) isotopic chains were obtained by using optical detection at COLLAPS, ISOLDE-CERN. From these measurements, our knowledge of nuclear ground-state spins, ground-state electromagnetic moments and changes in the root-mean-squared charge radii has been extended up to $N=$32 [3-7].\newline With relatively low production yields, the isotopes $^{\mathrm{51}}$K (\textasciitilde 4000 ions/s) and$^{\mathrm{\thinspace \thinspace 52}}$Ca (\textasciitilde 250 ions/s) are at the limit of optical detection techniques. In order to extend laser spectroscopy studies further away from stability, a highly sensitive experimental setup has been developed at the COLLAPS beam line [8,9]. The current developments in this direction and the perspectives for future experiments using collinear resonance ionization spectroscopy (CRIS) [10,11] in the region towards $N=$34 will be discussed.\newline [1] F. Wienholtz \textit{et al.,} \textit{Nature} 498, 346 (2013). [2] D. Steppenbeck \textit{et al.,} \textit{Nature} 502, 207 (2013). [3] J. Papuga \textit{et al. } Phys. Rev. Lett. 119, 172503 (2013). [4] M. Bissell \textit{et al.,} Phys. Rev. Lett. 90, 034321 (2014). [5] K. Kreim \textit{et al. }Phys. Lett. B 731, 97 (2014). [6] R.F. Garcia Ruiz \textit{et al.,} \textit{Phys. Rev. C }91, 041304(R) (20015). [7] R.F. Garcia Ruiz \textit{et al.,}~\textit{Nature Physics} 12, 594 (2016). [8] L. Vermeeren, \textit{et al.,} \textit{Phys. Rev. Lett.} 68, 1679 (1992). [9] R. F. Garcia Ruiz~~\textit{et al.} \textit{In preparation}~(2016). [10] K. T. Flanagan \textit{et al.,} Phys. Rev. Lett. 111, 212501 (2013). [11] R. P. De Groote \textit{et al}., Phys. Rev. Lett. 115, 132501 (2015).