The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions. Exceedingly neutron-rich nuclei become sensitive to new aspects of ...nuclear forces. Calcium, with its doubly magic isotopes (40)Ca and (48)Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory. Whereas predictions for the masses of (51)Ca and (52)Ca have been validated by direct measurements, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes (53)Ca and (54)Ca, using the multi-reflection time-of-flight mass spectrometer of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics.
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•Multi-reflection time-of-flight mass separator for purification of radioactive ion beams.•Enhanced ion beam purification by stacking of multiple cleaned ion samples in an ...intermediate ion trap to increase the signal intensity of Penning trap mass measurements.•Multi-reflection time-of-flight mass spectrometer for high-precision mass measurements of short-lived species.•Multi-reflection time-of-flight mass analyzer for target and ion-source development of exotic beams.
The online precision mass spectrometer ISOLTRAP at ISOLDE/CERN was recently upgraded by adding a multi-reflection time-of-flight mass separator/spectrometer (MR-ToF MS) between the linear radio-frequency ion trap and the two Penning traps already in place. As a mass separator, the MR-ToF device has improved significantly ISOLTRAP's capability of purification of contaminated ion beams. In addition, the MR-ToF MS can be operated as a mass spectrometer, either to analyze the ISOLDE ion beam or for precision mass measurements of nuclides that are shorter-lived or that have lower yields than those accessible for Penning-trap mass spectrometry. The MR-ToF MS and corresponding components, its integration into ISOLTRAP, and its various operation modes are reviewed. Furthermore, a precision measurement of the 137Eu mass is presented, determined with the help of the MR-ToF device as a mass separator.
Molecular spectroscopy offers opportunities for the exploration of the fundamental laws of nature and the search for new particle physics beyond the standard model
. Radioactive molecules-in which ...one or more of the atoms possesses a radioactive nucleus-can contain heavy and deformed nuclei, offering high sensitivity for investigating parity- and time-reversal-violation effects
. Radium monofluoride, RaF, is of particular interest because it is predicted to have an electronic structure appropriate for laser cooling
, thus paving the way for its use in high-precision spectroscopic studies. Furthermore, the effects of symmetry-violating nuclear moments are strongly enhanced
in molecules containing octupole-deformed radium isotopes
. However, the study of RaF has been impeded by the lack of stable isotopes of radium. Here we present an experimental approach to studying short-lived radioactive molecules, which allows us to measure molecules with lifetimes of just tens of milliseconds. Energetically low-lying electronic states were measured for different isotopically pure RaF molecules using collinear resonance ionisation at the ISOLDE ion-beam facility at CERN. Our results provide evidence of the existence of a suitable laser-cooling scheme for these molecules and represent a key step towards high-precision studies in these systems. Our findings will enable further studies of short-lived radioactive molecules for fundamental physics research.
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•A new ion selection technique based on multi-reflection time-of-flight mass separation is introduced and characterized.•No further devices, such as ion gates, are needed for beam ...purification.•Several offline and online examples with short-lived nuclei are presented for illustration.
A method for high-resolution mass selection is presented which makes use of a multi-reflection time-of-flight mass spectrometer with in-trap lift. The new method needs no additional gating or deflection components. The concept is described in detail and demonstrated with both offline and online measurements on short-lived nuclides performed with ISOLTRAP at ISOLDE/CERN.
A multi-reflection time-of-flight (MR-ToF) mass analyzer has been integrated into ISOLTRAP, the precision mass spectrometer for on-line mass determinations of short-lived nuclides at ISOLDE/CERN. The ...new instrument improves ISOLTRAP by providing a fast separation of isobaric contaminant species as well as subsequent ion selection using the fast Bradbury–Nielsen gate. Suppression ratios of up to 104 and mass-resolving powers of over 105 have been reached in off-line experiments. Preliminary data from on-line applications illustrate the benefit and performance of the device and its potential in the context of the ISOLTRAP setup.
Abstract
The tin isotope
100
Sn is of singular interest for nuclear structure due to its closed-shell proton and neutron configurations. It is also the heaviest nucleus comprising protons and ...neutrons in equal numbers—a feature that enhances the contribution of the short-range proton–neutron pairing interaction and strongly influences its decay via the weak interaction. Decay studies in the region of
100
Sn have attempted to prove its doubly magic character
1
but few have studied it from an ab initio theoretical perspective
2,3
, and none of these has addressed the odd-proton neighbours, which are inherently more difficult to describe but crucial for a complete test of nuclear forces. Here we present direct mass measurements of the exotic odd-proton nuclide
100
In, the beta-decay daughter of
100
Sn, and of
99
In, with one proton less than
100
Sn. We use advanced mass spectrometry techniques to measure
99
In, which is produced at a rate of only a few ions per second, and to resolve the ground and isomeric states in
101
In. The experimental results are compared with ab initio many-body calculations. The 100-fold improvement in precision of the
100
In mass value highlights a discrepancy in the atomic-mass values of
100
Sn deduced from recent beta-decay results
4,5
.
In rare cases, the removal of a single proton (Z) or neutron (N) from an atomic nucleus leads to a dramatic shape change. These instances are crucial for understanding the components of the nuclear ...interactions that drive deformation. The mercury isotopes (Z = 80) are a striking example1,2: their close neighbours, the lead isotopes (Z = 82), are spherical and steadily shrink with decreasing N. The even-mass (A = N + Z) mercury isotopes follow this trend. The odd-mass mercury isotopes 181,183,185Hg, however, exhibit noticeably larger charge radii. Due to the experimental difficulties of probing extremely neutron-deficient systems, and the computational complexity of modelling such heavy nuclides, the microscopic origin of this unique shape staggering has remained unclear. Here, by applying resonance ionization spectroscopy, mass spectrometry and nuclear spectroscopy as far as 177Hg, we determine 181Hg as the shape-staggering endpoint. By combining our experimental measurements with Monte Carlo shell model calculations, we conclude that this phenomenon results from the interplay between monopole and quadrupole interactions driving a quantum phase transition, for which we identify the participating orbitals. Although shape staggering in the mercury isotopes is a unique and localized feature in the nuclear chart, it nicely illustrates the concurrence of single-particle and collective degrees of freedom at play in atomic nuclei.
The recently confirmed neutron-shell closure at N=32 has been investigated for the first time below the magic proton number Z=20 with mass measurements of the exotic isotopes (52,53)K, the latter ...being the shortest-lived nuclide investigated at the online mass spectrometer ISOLTRAP. The resulting two-neutron separation energies reveal a 3 MeV shell gap at N=32, slightly lower than for 52Ca, highlighting the doubly magic nature of this nuclide. Skyrme-Hartree-Fock-Bogoliubov and ab initio Gorkov-Green function calculations are challenged by the new measurements but reproduce qualitatively the observed shell effect.
Multi-reflection time-of-flight (MR-ToF) spectrometers are devices in which ions are reflected between two electrostatic mirrors to prolong their flight path. The performance of the apparatus relies ...on the stability of the voltages that are used to define the mirror potentials. Especially the voltage of the mirror electrodes at the point where the ions reverse the direction of their axial motion needs to be stable in order to minimize fluctuations of their total flight time. Here we present a method to increase the short- and long-term stability of suitable voltage supplies for enhanced performance of the spectrometer.
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