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Collinear laser spectroscopy is performed on the nickel isotopes Ni58-68,70, using a time-resolved photon counting system. From the measured isotope shifts, nuclear charge radii Rc are extracted and compared to theoretical results. Three ab initio approaches all employ, among others, the chiral interaction NNLOsat, which allows an assessment of their accuracy. We find agreement with experiment in differential radii δ⟨rc2⟩ for all employed ab initio methods and interactions, while the absolute radii are consistent with data only for NNLOsat. Within nuclear density functional theory, the Skyrme functional SV-min matches experiment more closely than the Fayans functional Fy(Δr,HFB). Collinear laser spectroscopy is performed on the nickel isotopes $^{58-68,70}$Ni, using a time-resolved photon counting system. From the measured isotope shifts, nuclear charge radii $R_c$ are extracted and compared to theoretical results. Three ab initio approaches all employ, among others, the chiral interaction NNLO$_{\rm sat}$, which allows an assessment of their accuracy. We find agreement with experiment in differential radii $\delta \left\langle r_\mathrm{c}^2 \right\rangle$ for all employed ab initio methods and interactions, while the absolute radii are consistent with data only for NNLO$_{\rm sat}$. Within nuclear density functional theory, the Skyrme functional SV-min matches experiment more closely than the Fayans functional Fy($\Delta r$,HFB).

The electric quadrupole moment of $^{49}$Sc was measured by collinear laser spectroscopy at CERN-ISOLDE to be $Q_{\rm s}=-0.159(8)$ $e$b, and a nearly tenfold improvement in precision was reached for the electromagnetic moments of $^{47,49}$Sc. The single-particle behavior and nucleon-nucleon correlations are investigated with the electromagnetic moments of $Z=21$ isotopes and $N=28$ isotones as valence neutrons and protons fill the distinctive $0f_{7/2}$ orbit, respectively, located between magic numbers, 20 and 28. The experimental data are interpreted with shell-model calculations using an effective interaction, and ab-initio valence-space in-medium similarity renormalization group calculations based on chiral interactions. These results highlight the sensitivity of nuclear electromagnetic moments to different types of nucleon-nucleon correlations, and establish an important benchmark for further developments of theoretical calculations., Comment: Accepted by Physics Letters B (2022)

Magnetic and quadrupole moments of the $7/{2}^{+}$ ground state in $^{133}\mathrm{Sb}$ and the $({7}^{\ensuremath{-}})$ isomer in $^{134}\mathrm{Sb}$ have been measured by collinear laser spectroscopy to investigate the single-particle behavior above the doubly magic nucleus $^{132}\mathrm{Sn}$. The comparison of experimental data of the $7/{2}^{+}$ states in $^{133}\mathrm{Sb}$ and neighboring $N=82$ isotones to shell-model calculations reveals the sensitivity of magnetic moments to the splitting of the spin-orbit partners $\ensuremath{\pi}0{g}_{9/2}$ and $\ensuremath{\pi}0{g}_{7/2}$ across the proton shell closure at $Z=50$. In contrast, quadrupole moments of the $N=82$ isotones are insensitive to cross-shell excitations, but require the full proton model space from $Z=50\phantom{\rule{4.pt}{0ex}}\text{to}\phantom{\rule{4.pt}{0ex}}82$ for their accurate description. In fact, the linear trend of the quadrupole moment follows approximately the expectation of the seniority scheme when filling the $\ensuremath{\pi}0{g}_{7/2}$ orbital. As far as the isomer in $^{134}\mathrm{Sb}$ is concerned, its electromagnetic moments can be perfectly described by the additivity rule employing the moments of $^{133}\mathrm{Sb}$ and $^{133}\mathrm{Sn}$, respectively. These findings agree with shell-model calculations and thus confirm the weak coupling between the valence proton and neutron in $^{134}\mathrm{Sb}$.

Hyperfine spectra of $^\text{27-32}$Al ($Z=13$) have been measured at the ISOLDE-CERN facility via collinear laser spectroscopy using the $3s^23p\ ^2\text{P}^\text{o} _{3/2}\rightarrow 3s^24s\ ^2\text{S}_{1/2}$ atomic transition. For the first time, mean-square charge radii of radioactive aluminum isotopes have been determined alongside the previously unknown magnetic dipole moment of $^{29}$Al and electric quadrupole moments of $^{29,30}$Al. A potentially reduced charge radius at $N=19$ may suggest an effect of the $N=20$ shell closure, which is visible in the Al chain, contrary to other isotopic chains in the $sd$ shell. The experimental results are compared to theoretical calculations in the framework of the valence-space in-medium similarity renormalization group using multiple sets of two and three-nucleon forces from chiral effective field theory. While the trend of experimental magnetic dipole and electric quadrupole moments is well reproduced, the absolute values are underestimated by theory, consistent with earlier studies. Moreover, both the scale and trend of the charge radii appear to be very sensitive to the chosen interaction.

Collinear laser spectroscopy (CLS) has been performed in a multi-reflection time-of-flight (MR-ToF) device operated in single-pass mode, i.e., without confining the ions in the ion trap. While our Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) aims to increase the CLS sensitivity by storing ions in the MR-ToF device, the present work characterises conventional single-passage CLS as a preparatory step for the upcoming comparison with MIRACLS’ multi-pass mode. To this end, the isotope shift in the 3 s 2 S 1 / 2 → 3 p 2 P 3 / 2 transition (D2 line) between ions of the magnesium isotopes 24Mg and 26Mg has been measured under varying experimental conditions. Our result agrees with the precise literature value. Associated studies of systematic uncertainties demonstrate a measurement accuracy of better than 20 MHz in this new apparatus. This value will serve as the reference for analogous studies to be performed in the MIRACLS approach in which ions are trapped in the MR-ToF device for thousands of revolutions and probed by the spectroscopy laser during each passage.

Communications Physics 3(1), 107 (2020). doi:10.1038/s42005-020-0348-9, Published by Springer Nature, London

Collinear laser spectroscopy measurements were performed on $^{69,71,73}$Ge isotopes ($Z = 32$) at ISOLDE-CERN. The hyperfine structure of the $4s^2 4p^2 \, ^3P_1 \rightarrow 4s^2 4p 5s \, ^3P_1^o$ transition of the germanium atom was probed with laser light of 269 nm, produced by combining the frequency-mixing and frequency-doubling techniques. The hyperfine fields for both atomic levels were calculated using state-of-the-art atomic relativistic Fock-space coupled-cluster calculations. A new $^{73}$Ge quadrupole moment was determined from these calculations and previously measured precision hyperfine parameters, yielding $Q_{\rm s}$ = $-$0.198(4) b, in excellent agreement with the literature value from molecular calculations. The moments of $^{69}$Ge have been revised: $\mu$ = +0.920(5) $\mu_{N}$ and $Q_{\rm s}$= +0.114(8) b, and those of $^{71}$Ge have been confirmed. The experimental moments around $N = 40$ are interpreted with large-scale shell-model calculations using the JUN45 interaction, revealing rather mixed wave function configurations, although their $g$-factors are lying close to the effective single-particle values. Through a comparison with neighboring isotones, the structural change from the single-particle nature of nickel to deformation in germanium is further investigated around $N = 40$.

We present the first laser spectroscopic measurement of the neutron-rich nucleus ^{68}Ni at the N=40 subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability α_{D} has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two- and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus ^{48}Ca. Three-particle-three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of ^{68}Ni.

Collinear laser spectroscopy (CLS) has been combined with the multi-reflection time-of-flight (MR-ToF) technique. To this end, a photodetection system has been implemented at the drift region of a MR-ToF apparatus and a laser beam has been sent along the path of the ions that are stored between the two ion-optical mirrors. The main goal of the present proof-of-principle (PoP) experiments, is the confirmation of the expected increase in sensitivity compared to conventional fluorescence-based CLS due to the repeated probing of the trapped ion bunches. The novel method will be used for the precise measurement of nuclear ground- and isomeric-state properties of exotic nuclei with low production yields at radioactive ion-beam facilities. A significant sensitivity improvement of CLS is expected, depending on the half-life and mass of the nuclide of interest. The status of the PoP setup and future improvements are discussed. Collinear laser spectroscopy (CLS) has been combined with the multi-reflection time-of-flight (MR-ToF) technique. To this end, a photodetection system has been implemented at the drift region of a MR-ToF apparatus and a laser beam has been sent along the path of the ions that are stored between the two ion-optical mirrors. The main goal of the present proof-of-principle (PoP) experiments, is the confirmation of the expected increase in sensitivity compared to conventional fluorescence-based CLS due to the repeated probing of the trapped ion bunches. The novel method will be used for the precise measurement of nuclear ground- and isomeric-state properties of exotic nuclei with low production yields at radioactive ion-beam facilities. A significant sensitivity improvement of CLS is expected, depending on the half-life and mass of the nuclide of interest. The status of the PoP setup and future improvements are discussed.

Physical review letters 122(19), 192502 (2019). doi:10.1103/PhysRevLett.122.192502, Published by APS, College Park, Md.

The Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at CERN has achieved high-resolution resonance ionisation laser spectroscopy with a full width at half maximum linewidth of 20(1) MHz for 219;221Fr, and has measured isotopes as short lived as 5 ms with 214Fr. This development allows for greater precision in the study of hyperfine structures and isotope shifts, as well as a higher selectivity of singleisotope, even single-isomer, beams. These achievements are linked with the development of a new laser laboratory and new data-acquisition systems. publisher: Elsevier articletitle: High-resolution laser spectroscopy with the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at CERN-ISOLDE journaltitle: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms articlelink: http://dx.doi.org/10.1016/j.nimb.2015.11.024 content_type: article copyright: © 2017 The Authors. Published by Elsevier B.V. ispartof: Nuclear Instruments & Methods in Physics Research B vol:376 pages:284-287 ispartof: location:Grand Rapids: MI status: published

In the development towards the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), an optical detection region for the observation of fluorescent light is added to an electrostatic ion beam trap (EIBT). In addition to its use for highly sensitive collinear laser spectroscopy, this fluorescence detection is introduced as a diagnostics tool for the study of the ion dynamics inside an EIBT. First measurements of collision-induced fluorescence in an EIBT demonstrate the technique’s diagnostics power by tracking the evolution of an ion bunch’s temporal width over its storage time inside the ion trap. Thereby, the time-focus point of the ion bunch can be determined and the influence of space-charge effects in the EIBT can be investigated. Good qualitative agreement is obtained between the measured trend of temporal widths and the simulations of the ions’ trajectories in the trap. Particularly, the observation of self-bunching on the ion-bunch structure for many simultaneously stored ions is reproduced.

For nearly four decades Collinear Laser Spectroscopy (CLS) has been employed to determine ground-state properties of short-lived radionuclides. To extend its reach to the most exotic radionuclides with very low production yields, the novel Multi Ion Reflection Apparatus for CLS (MIRACLS) is currently under development at ISOLDE/CERN. In this setup, 30-keV ion bunches will be trapped between two electrostatic mirrors of a multi-reflection time-of-flight (MR-ToF) device such that the laser beam will probe the ions during each revolution. Thus, the observation time will be extended and the experimental sensitivity will be increased significantly while maintaining the high resolution of conventional CLS. A proof-of-principle experiment is currently being performed to demonstrate the potential of CLS within a low-energy MR-ToF device. Its first experimental results benchmark the validity of ion-optical simulations from the CLS perspective, which will also be applied to MIRACLS’ 30-keV apparatus.

The nuclear g factor and quadrupole moment ( Q s ) have been measured for the low-lying isomeric 1 + state of 34Al, using the β-detected nuclear magnetic resonance (β-NMR) and quadrupole resonance (β-NQR) methods. Spin-polarized 34Al isotopes were produced in a one-neutron pickup reaction induced by a 36S beam on a 9Be target at a kinetic energy of 77.5 MeV/nucleon, and were collected with the LISE fragment separator at GANIL. The measured g factor ( | g | in a range of 1.757 ± 0.014 ) and quadrupole moment ( | Q s | = 38 ( 5 ) mb) are in good agreement with shell-model calculations using effective interactions. The similarity between the g factor of 34 m Al and that of 32Al confirms a dominant neutron 2 p 1 h configuration π ( d 5 / 2 ) − 1 ⊗ ν ( d 3 / 2 ) − 1 ( f 7 / 2 ) 2 of 34 m Al. In addition, the enhanced quadrupole moment of 34 m Al relative to that of 32Al suggests that the neutron 1 p 1 h excitation across the N = 20 shell gap introduces extra nucleon–nucleon correlation and deformation.

The Multi-Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), currently under development at ISOLDE/CERN, aims to combine the high resolution of fluorescence-based collinear laser spectroscopy (CLS) with a high sensitivity. This will be achieved by confining 30-keV ion bunches in a Multi-Reflection Time-of-Flight (MR-ToF) device which allows laser spectroscopic probing for several thousand times. An MR-ToF setup operating at ∼ 1.5 keV beam energy has been adapted for a proof-of-principle experiment. Thus, efforts had to be undertaken to reduce the laser stray light as the leading source of background of this apparatus, not originally designed for CLS. These measures enabled CLS of $^{24,26}$Mg$^+$ ions in single-path mode, i.e. without ion trapping, which is the reference point to gauge the gain in sensitivity of the MIRACLS technique.

Collinear laser spectroscopy was performed on Zn (Z=30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N=33–49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-A neutron-rich nuclei up to N=50. Exactly one long-lived (&, SCOPUS: ar.j, info:eu-repo/semantics/published

An experimental setup for sensitive high-resolution measurements of hyperfine structure spectra of exotic calcium isotopes has been developed and commissioned at the COLLAPS beam line at ISOLDE, CERN. The technique is based on the radioactive detection of decaying isotopes after optical pumping and state selective neutralization (ROC) (Vermeeren et al 1992 Phys. Rev. Lett. 68 1679). The improvements and developments necessary to extend the applicability of the experimental technique to calcium isotopes produced at rates as low as few ions s–1 are discussed. Numerical calculations of laser-ion interaction and ion-beam simulations were explored to obtain the optimum performance of the experimental setup. Among the implemented features are a multi-step optical pumping region for sensitive measurements of isotopes with hyperfine splitting, a high-voltage platform for adequate control of low-energy ion beams and simultaneous β-detection of neutralized and remaining ions. journal_title: Journal of Physics G: Nuclear and Particle Physics article_type: paper article_title: Development of a sensitive setup for laser spectroscopy studies of very exotic calcium isotopes copyright_information: © 2017 IOP Publishing Ltd date_received: 2016-11-15 date_accepted: 2017-01-18 date_epub: 2017-02-22 ispartof: Journal of Physics G, Nuclear and Particle Physics vol:44 issue:4 status: published

The hyperfine spectra of $^{51,53-64}$Mn were measured in two experimental runs using collinear laser spectroscopy at ISOLDE, CERN. Laser spectroscopy was performed on the atomic $3d^5\ 4s^2\ ^{6}\text{S}_{5/2}\rightarrow 3d^5\ 4s4p\ ^{6}\text{P}_{3/2}$ and ionic $3d^5\ 4s\ ^{5}\text{S}_2 \rightarrow 3d^5\ 4p\ ^{5}\text{P}_3$ transitions, yielding two sets of isotope shifts. The mass and field shift factors for both transitions have been calculated in the multiconfiguration Dirac-Fock framework and were combined with a King plot analysis in order to obtain a consistent set of mean-square charge radii which, together with earlier work on neutron-deficient Mn, allow the study of nuclear structure changes from $N=25$ across $N=28$ up to $N=39$. A clear development of deformation is observed towards $N=40$, confirming the conclusions of the nuclear moments studies. From a Monte Carlo Shell Model study of the shape in the Mn isotopic chain, it is suggested that the observed development of deformation is not only due to an increase in static prolate deformation but also due to shape fluctuations and triaxiality. The changes in mean-square charge radii are well reproduced using the Duflo-Zuker formula except in the case of large deformation., Comment: 9 figures, submitted to PRC

The electric quadrupole moment of the $_{13}^{33}\mathrm{Al}_{20}$ ground state, located at the border of the island of inversion, was obtained using continuous-beam $\ensuremath{\beta}$-detected nuclear quadrupole resonance ($\ensuremath{\beta}$-NQR). From the measured quadrupole coupling constant ${\ensuremath{\nu}}_{Q}=2.31(4)$ MHz in an $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ crystal, a precise value for the electric quadrupole moment is extracted: $\left|{Q}_{s}\left(^{33}\mathrm{Al}\right)\right|=141(3)$ mb. A comparison with large-scale shell model calculations shows that $^{33}\mathrm{Al}$ has at least 50% intruder configurations in the ground state wave function, favoring the excitation of two neutrons across the $N=20$ shell gap. $^{33}\mathrm{Al}$ therefore clearly marks the gradual transition north of the deformed Na and Mg nuclei towards the normal $Z\ensuremath{\ge}14$ isotopes.

Two different experiments observe nuclei with excited nuclear states that differ in shape from their ground states, so called shape coexistence. These nuclei lie close to the neutron-rich doubly-magic ${}^{78}$Ni region of the nuclear chart.

Collinear laser spectroscopy is performed on the _{30}^{79}Zn_{49} isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life is confirmed, and the nuclear spins and moments of the ground and isomeric states in ^{79}Zn as well as the isomer shift are measured. From the observed hyperfine structures, spins I=9/2 and I=1/2 are firmly assigned to the ground and isomeric states. The magnetic moment μ (^{79}Zn)=-1.1866(10)μ_{N}, confirms the spin-parity 9/2^{+} with a νg_{9/2}^{-1} shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment μ (^{79m}Zn)=-1.0180(12)μ_{N} supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the N=50 shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state, δ⟨r_{c}^{2}⟩^{79,79m}=+0.204(6) fm^{2}, providing first evidence of shape coexistence.

High-resolution laser spectroscopy was performed on $^{206}\mathrm{Fr}$ with the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE. The hyperfine structure and isotope shift of the ground, first isomeric and second isomeric states were measured. The hyperfine components were unambiguously assigned to each nuclear state by means of laser-assisted nuclear decay spectroscopy. The branching ratios in the $\ensuremath{\alpha}$ decay of $^{206}\mathrm{Fr}$ and $^{202}\mathrm{At}$ were also measured for the first time with isomerically purified beams. The extracted hindrance factors allow determination of the spin of the ground, first isomeric, and second isomeric states in $^{202}\mathrm{At}$ and $^{198}\mathrm{Bi}$.

The odd-odd $^{54,56,58,60,62,64}\mathrm{Mn}$ isotopes ($Z=25$) were studied using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. From the measured hyperfine spectra the spins and magnetic moments of Mn isotopes up to $N=39$ were extracted. The previous tentative ground state spin assignments of $^{58,60,62,64}\mathrm{Mn}$ are now firmly determined to be $I=1$ along with an $I=4$ assignment for the isomeric states in $^{58,60,62}\mathrm{Mn}$. The $I=1$ magnetic moments show a decreasing trend with increasing neutron number while the $I=4$ moments remain quite constant between $N=33$ and $N=37$. The results are compared to large-scale shell-model calculations using the GXPF1A and LNPS effective interactions. The excellent agreement of the ground state moments with the predictions from the LNPS calculations illustrates the need for an increasing amount of proton excitations across $Z=28$ and neutron excitations across $N=40$ in the ground state wave functions from $N=37$ onwards.

New technical developments have led to a 2 orders of magnitude improvement of the resolution of the collinear resonance ionization spectroscopy (CRIS) experiment at ISOLDE, CERN, without sacrificing the high efficiency of the CRIS technique. Experimental linewidths of 20(1) MHz were obtained on radioactive beams of francium, allowing us for the first time to determine the electric quadrupole moment of the short lived [t1/2=22.0(5) ms]219Fr Qs=−1.21(2) eb, which would not have been possible without the advantages offered by the new method. This method relies on a continuous-wave laser and an external Pockels cell to produce narrow-band light pulses, required to reach the high resolution in two-step resonance ionization. Exotic nuclei produced at rates of a few hundred ions/s can now be studied with high resolution, allowing detailed studies of the anchor points for nuclear theories. ispartof: Physical Review Letters vol:115 issue:13 pages:1-6 ispartof: location:United States status: published

We have studied 51,53−64Mn (Z=25) via bunched-beam collinear laser spectroscopy at ISOLDE, CERN. Model-independent information on the ground- and isomeric state spins, as well as their g-factors is obtained from the measured hyperfine spectra. The spins are essential for further establishing the level schemes in the mass region, while the g-factors reveal the changing ground state wave functions in the Mn chain approaching N=40. ispartof: pages:699-702 ispartof: Acta Physica Polonica B vol:46 issue:3 pages:699-702 ispartof: location:Zakopane, Poland status: published

Following a growing interest in spin-polarized beams of radioactive ions, a new laser spin-polarization setup has been installed at the ISOLDE facility at CERN. The setup is located at the VITO beamline which aims to bring together several experimental techniques using polarized ions allowing for studies in nuclear physics, fundamental interactions, material and life sciences. Intensive design work, which took place in 2016, allowed the installation of the first stage of the polarization line. With this experimental setup, the ion beam can be neutralized, polarized and implanted into a solid sample inside an electromagnet which also hosts β-detectors, where the degree of nuclear spin polarization can be measured. In autumn 2016 the setup was commissioned using short-lived 26Na and 28Na beams which were polarized in the D2 line from their atomic ground state. The previously observed degrees of β asymmetry were reproduced and thus the beamline is now ready for the first physics experiments with spin-polarized radioactive beams. ispartof: Journal of Physics G, Nuclear and Particle Physics vol:44 issue:8 status: published