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At radioactive ion beam (RIB) facilities, ions of short-lived radionuclides are cooled and bunched in buffergas-filled Paul traps to improve the ion-beam quality for subsequent experiments. To deliver even colder ions, beneficial to RIB experiments’ sensitivity or accuracy, we employ Doppler and sympathetic cooling in a Paul trap cooler-buncher. The improved emittance of Mg$^+$, K$^+$, and O$^+_2$ ion beams is demonstrated by a reduced time-of-flight spread of the extracted ion bunches with respect to room-temperature buffer-gas cooling. Cooling externally-produced hot ions with energies of at least 7 eV down to a few Kelvin is achieved in a timescale of $O$(100 ms) by combining a low-pressure helium background gas with laser cooling. This is sufficiently short to cool short-lived radioactive ions. As an example of this technique’s use for RIB research, the mass-resolving power in a multireflection time-of-flight mass spectrometer is shown to increase by up to a factor of 4.6 with respect to buffer-gas cooling. Simulations show good agreement with the experimental results and guide further improvements and applications. These results open a path to a significant emittance improvement and, thus, unprecedented ion-beam qualities at RIB facilities, achievable with standard equipment readily available. The same method provides opportunities for future high-precision experiments with radioactive cold trapped ions.

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)

In spite of the high-density and strongly correlated nature of the atomic nucleus, experimental and theoretical evidence suggests that around particular 'magic' numbers of nucleons, nuclear properties are governed by a single unpaired nucleon

A series of g-factor measurements in the Cl isotopes created as secondary radioactive beams at intermediate energies and employing the β-NMR technique have been recently carried out at GANIL. The results attempt to shed light on several open questions for the ground state properties of Cl isotopes, located just off the very interesting region of the island of inversion. Preliminary experimental results are presented and compared to shell-model calculations around N=28.

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.

A marked difference in the nuclear charge radius was observed between the I^{π}=3^{+} ground state and the I^{π}=0^{+} isomer of ^{38}K and is qualitatively explained using an intuitive picture of proton-neutron pairing. In a high-precision measurement of the isomer shift using bunched-beam collinear laser spectroscopy at CERN-ISOLDE, a change in the mean-square charge radius of ⟨r_{c}^{2}⟩(^{38}K^{m})-⟨r_{c}^{2}⟩(^{38}K^{g})=0.100(6) fm^{2} was obtained. This is an order of magnitude more accurate than the result of a previous indirect measurement from which it was concluded that both long-lived states in ^{38}K have similar charge radii. Our observation leads to a substantially different understanding since the difference in charge radius is, moreover, opposite in sign to previously reported theoretical predictions. It is demonstrated that the observed isomer shift can be reproduced by large-scale shell-model calculations including proton and neutron excitations across the N,Z=20 shell gaps, confirming the significance of cross-shell correlations in the region of ^{40}Ca.

A new collinear resonant ionization spectroscopy (CRIS) beam line has recently been installed at ISOLDE, CERN utilising lasers to combine collinear laser spectroscopy and resonant ionization spectroscopy. The combined technique offers the ability to purify an ion beam that is heavily contaminated with radioactive isobars, including the ground state of an isotope from its isomer, allowing sensitive secondary experiments to be performed. A new programme aiming to use the CRIS technique for the separation of nuclear isomeric states for decay spectroscopy will commence in 2011. A decay spectroscopy station, consisting of a rotating wheel implantation system for alpha decay spectroscopy, and three high purity germanium detectors around the implantation site for gamma-ray detection, has been developed for this purpose. This paper will report the current status of the laser assisted decay spectroscopy set-up for the CRIS beam line.

The CRIS (Collinear Resonant Ionisation Spectroscopy) beam line is a new experimental set up at the ISOLDE facility at CERN. CRIS is being constructed for high-resolution laser spectroscopy measurements on radioactive isotopes. These measurements can be used to extract nuclear properties of isotopes far from stability. The CRIS beam line has been under construction since 2009 and testing of its constituent parts have been performed using stable and radioactive ion beams, in preparation for its first on-line run. This paper will present the current status of the CRIS experiment and highlight results from the recent tests.

The installation of an ion–beam cooler–buncher at the ISOLDE, CERN facility has provided increased sensitivity for collinear laser spectroscopy experiments. A migration of single-particle states in gallium and in copper isotopes has been investigated through extensive measurements of ground state and isomeric state hyperfine structures. Lying beyond the N = 50 shell closure, 82Ga is the most exotic nucleus in the region to have been studied by optical methods, and is reported here for the first time.

Charge radii of all magnesium isotopes in the sd shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on (24)Mg and (32)Mg. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards N=8 and collectivity near N=20 is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.

The electric quadrupole moment and the magnetic moment of the 11Li halo nucleus have been measured with more than an order of magnitude higher precision than before, |Q| = 33.3(5) mb and mu = +3.6712(3)muN, revealing a 8.8(1.5)% increase of the quadrupole moment relative to that of 9Li. This result is compared to various models that aim at describing the halo properties. In the shell model an increased quadrupole moment points to a significant occupation of the 1d orbits, whereas in a simple halo picture this can be explained by relating the quadrupole moments of the proton distribution to the charge radii. Advanced models so far fail to reproduce simultaneously the trends observed in the radii and quadrupole moments of the lithium isotopes.

We report on the first determination of the nuclear ground-state spin of 33Mg, I=3/2, and its magnetic moment, mu= -0.7456(5) mu(N), by combining laser spectroscopy with nuclear magnetic resonance techniques. These values are inconsistent with an earlier suggested 1 particle-1 hole configuration and provide evidence for a 2 particle-2 hole intruder ground state with negative parity. The results are in agreement with an odd-neutron occupation of the 3/2 [321] Nilsson orbital at a large prolate deformation. The discussion emphasizes the need of further theoretical and experimental investigation of the island of inversion, a region previously thought to be well understood.

The quadrupole moment of the 8{sup +} yrast state in {sup 84}Kr was measured using the level-mixing spectroscopy technique to be Q= 36(4) e fm{sup 2}. The result is compared with predictions of the shell model using common sets of effective charges. The comparison of experimental quadrupole moments with calculated values for 8{sup +} states in Kr, Sr and Zr isotopes with N= 48, 50 and for 9/2{sup +} states in isotopes with N= 47, 49 suggests a modification of the effective charges used in this region.

Jolie, J. Ilie, G. Reiter, P. Richard, A. Scherillo, A. Striepling, T. Warr, N. Banu, A. Becker, F. Bednarczyk, P. Doornenbal, P. Gerl, J. Grawe, H. Gorska, M. Kojouharov, I. Mandal, S. Saito, N. Saito, T. R. Wollersheim, H. -J. Mallion, S. Neyens, G. Turzo, K. Van Duppen, P. Vermeulen, N. Podolyak, Zs. Gelletly, W. Regan, P. H. Walker, P. M. Catford, W. N. Liu, Z. Williams, S. Blazhev, A. Lozeva, R. Detistov, P. Atanasova, L. Damyanova, G. Gil, D. Cortina Benlliure, J. Kurtukian Nieto, T. Caserejos, E. Daugas, J. M. Belier, G. Meot, V. Roig, O. Simpson, G. Tsekhanovich, I. S. Matea, I. Schwengner, R. Hass, M. Singh, B. S. Nara Chamoli, S. K. Goldring, G. Regev, I. Vaintraub, S. Balabanski, D. L. Lo Bianco, G. Gladnishki, K. Saltarelli, A. Petrache, C. Benzoni, G. Blasi, N. Bracco, A. Camera, F. Million, B. Leoni, S. Wieland, O. Maj, A. Kmiecik, M. Grebosz, J. Bednarczyk, P. Styczen, J. Lach, M. Meczynski, W. Mazurek, K. Pfutzner, M. Korgul, A. Ionescu-Bujor, M. Iordachescu, A. Zamfir, V. Jungclaus, A. Georgiev, G. Cullen, D. M. Freeman, S. J. Smith, A. G. Orlandi, R. Clark, R. M. Bentley, M. A. Hammond, G. Wadsworth, R. Buerger, A. Huebel, H. Rudolph, D. Fahlander, C. Simpson, J. Herzberg, R. D. Page, R. D. Nolan, P. Davidson, T. Woods, P. Bruce, A. M. Faestermann, T. Kruecken, R. Mach, H. Rubio, B. Algora, A.

Unambiguous values of the spin and magnetic moment of 31Mg are obtained by combining the results of a hyperfine-structure measurement and a beta-NMR measurement, both performed with an optically polarized ion beam. With a measured nuclear g factor and spin I=1/2, the magnetic moment mu(31Mg)=-0.88355(15)mu(N) is deduced. A revised level scheme of 31Mg (Z=12, N=19) with ground state spin/parity I(pi)=1/2(+) is presented, revealing the coexistence of 1p-1h and 2p-2h intruder states below 500 keV. Advanced shell-model calculations and the Nilsson model suggest that the I(pi)=1/2(+) ground state is a strongly prolate deformed intruder state. This result plays a key role for the understanding of nuclear structure changes due to the disappearance of the N=20 shell gap in neutron-rich nuclei.

We report on the g factor measurement of an isomer in the neutron-rich (61)(26)Fe (E(*)=861 keV and T(1/2)=239(5) ns). The isomer was produced and spin aligned via a projectile-fragmentation reaction at intermediate energy, the time dependent perturbed angular distribution method being used for the measurement of the g factor. For the first time, due to significant improvements of the experimental technique, an appreciable residual alignment of the nuclear spin ensemble has been observed, allowing a precise determination of its g factor, including the sign: g=-0.229(2). In this way we open the possibility to study moments of very neutron-rich short-lived isomers, not accessible via other production and spin-orientation methods.

The yrast J(pi)=8(+) states in neutron-rich Ni-70,Ni-72,Ni-74,Ni-76 nuclei are predicted to be isomeric. The present paper describes two GANIL experiments. In the first of them a search was made for the 8(+) isomeric states in Ni-72,Ni-74 nuclei via fragmentation of Ge-76 using the ion gamma-decay correlation technique. Although these states were not observed, limits for their lifetimes were determined. In the second experiment the decay spectroscopy of Co-70,Co-72 nuclei was performed using fragmentation of a Kr-86(36+) beam and the new LISE2000 spectrometer. The beta delayed gamma rays from the decay of Co-70,Co-72 to Ni-70,Ni-72 were observed using the EXOGAM germanium detectors. The half life of Co-72 was measured to be 62(3) ms and the level sequence of the lowest excited states in Ni-72 was suggested, with the 2(+) state at 1096 keV. An attempt to reproduce the level scheme in terms of shell-model calculations was undertaken. The reasons for the disappearance of the 8(+) isomer in Ni-72 are discussed.

The spectroscopic quadrupole moments of the 11− isomers in 194Pb and 196Pb have been measured by applying the Level Mixing Spectroscopy technique. These isomers have the π(s1/2−2h9/2i13/2) proton configuration. The implications of these results for the influence of the intruder character of the isomers on their deformation is given. We will especially focus on a simple 2-dimensional model, taking into account the coupling of the valence nucleons with the vibrations of the underlying core, which gives theoretical insight in the obtained experimental results for the quadrupole moments of the 11− isomers.

Structure of the exotic nuclei near 70Ni probed by advanced time delayed coincidence methods: the interpretation of the 1.76 μs isomer in 72Cu

By combining two well established methods, the β-level mixing resonance (β-LMR) and the β-nuclear magnetic resonance (β-NMR), it is possible to determine the magnetic moment and the quadrupole moment of nuclei with low spin. The combined method can be applied on spin oriented ground state β-decaying nuclei. It was tested on the known 12B and successfully applied on the neutron rich 18N. We found for the magnetic moment μ(18N)=0.157(7)n.m. and for the quadrupole moment Q(18N)=30(3)mbarn.