First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He

The first direct mass-measurement of $^{6}$He has been performed with the TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the mass of $^{8}$He was determined with improved precision over our previous measurement. The obtained masses are $m$($^{6}$He) = 6.018 885 883(57) u and $m$($^{8}$He) = 8.033 934 44(11) u. The $^{6}$He value shows a deviation from the literature of 4$\sigma$. With these new mass values and the previously measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and 1.959(16) fm for $^{6}$He and $^{8}$He respectively. We present a detailed comparison to nuclear theory for $^6$He, including new hyperspherical harmonics results. A correlation plot of the point-proton radius with the two-neutron separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure

Separated Oscillatory Fields for High-Precision Penning Trap Mass Spectrometry

Ramsey's method of separated oscillatory fields is applied to the excitation of the cyclotron motion of short-lived ions in a Penning trap to improve the precision of their measured mass. The theoretical description of the extracted ion-cyclotron-resonance line shape is derived out and its correctness demonstrated experimentally by measuring the mass of the short-lived $^{38}$Ca nuclide with an uncertainty of $1.6\cdot 10^{-8}$ using the ISOLTRAP Penning trap mass spectrometer at CERN. The mass value of the superallowed beta-emitter $^{38}$Ca is an important contribution for testing the conserved-vector-current hypothesis of the electroweak interaction. It is shown that the Ramsey method applied to mass measurements yields a statistical uncertainty similar to that obtained by the conventional technique ten times faster.Comment: 5 pages, 4 figures, 0 table

Trapped-ion decay spectroscopy towards the determination of ground-state components of double-beta decay matrix elements

A new technique has been developed at TRIUMF's TITAN facility to perform in-trap decay spectroscopy. The aim of this technique is to eventually measure weak electron capture branching ratios (ECBRs) and by this to consequently determine GT matrix elements of $\beta\beta$ decaying nuclei. These branching ratios provide important input to the theoretical description of these decays. The feasibility and power of the technique is demonstrated by measuring the ECBR of $^{124}$Cs.Comment: 9 pages, 9 figure

Precision Mass Measurements of 129-131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process

Masses adjacent to the classical waiting-point nuclide 130Cd have been measured by using the Penning- trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N = 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A = 128 - 132 region and a reduction of the uncertainties from the precision mass input data

Elucidation of the anomalous A = 9 isospin quartet behaviour

Recent high-precision mass measurements of $^{9}$Li and $^{9}$Be, performed with the TITAN Penning trap at the TRIUMF ISAC facility, are analyzed in light of state-of-the-art shell model calculations. We find an explanation for the anomalous Isobaric Mass Multiplet Equation (IMME) behaviour for the two $A$ = 9 quartets. The presence of a cubic $d$ = 6.3(17) keV term for the $J^{\pi}$ = 3/2$^{-}$ quartet and the vanishing cubic term for the excited $J^{\pi}$ = 1/2$^{-}$ multiplet depend upon the presence of a nearby $T$ = 1/2 state in $^{9}$B and $^{9}$Be that induces isospin mixing. This is contrary to previous hypotheses involving purely Coulomb and charge-dependent effects. $T$ = 1/2 states have been observed near the calculated energy, above the $T$ = 3/2 state. However an experimental confirmation of their $J^{\pi}$ is needed.Comment: 5 pages, 2 figure

First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li

In this letter, we report a new mass for $^{11}$Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, $t_{1/2} = 8.8 \rm{ms}$, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of $^{8,9}$Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of seven more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for $^{11}$Li. This result is a remarkable confluence of nuclear and atomic physics.Comment: Formatted for submission to PR

Penning trap mass measurements on (99-109)$Cd with ISOLTRAP and implications on the rp process

Penning trap mass measurements on neutron-deficient Cd isotopes (99-109)Cd have been performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN, all with relative mass uncertainties below 3*10^8. A new mass evaluation has been performed. The mass of 99Cd has been determined for the first time which extends the region of accurately known mass values towards the doubly magic nucleus 100Sn. The implication of the results on the reaction path of the rp process in stellar X-ray bursts is discussed. In particular, the uncertainty of the abundance and the overproduction created by the rp-process for the mass A = 99 is demonstrated by reducing the uncertainty of the proton-separation energy of 100In Sp(100In) by a factor of 2.5.Comment: 14 pages, 9 figure

Probing the N = 32 shell closure below the magic proton number Z = 20: Mass measurements of the exotic isotopes 52,53K

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 52,53K, 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-Boguliubov and ab initio Gorkov-Green function calculations are challenged by the new measurements but reproduce qualitatively the observed shell effect.Comment: 5 pages, 5 figure

Evidence for a breakdown of the Isobaric Multiplet Mass Equation: A study of the A=35, T=3/2 isospin quartet

Mass measurements on radionuclides along the potassium isotope chain have been performed with the ISOLTRAP Penning trap mass spectrometer. For 35K T1/2=178ms) to 46K (T1/2=105s) relative mass uncertainties of 2x10-8 and better have been achieved. The accurate mass determination of 35K (dm=0.54keV) has been exploited to test the Isobaric Multiplet Mass Equation (IMME) for the A=35, T=3/2 isospinquartet. The experimental results indicate a deviation from the generally adopted quadratic form.Comment: 8 pages, 4 figure

Breakdown of the Isobaric Multiplet Mass Equation (IMME) at A=33, T=3/2

Mass measurements on $^{33, 34, 42, 43}$Ar were performed using the Penning trap mass spectrometer ISOLTRAP and a newly constructed linear Paul trap. This arrangement allowed for the first time to extend Penning trap mass measurements to nuclides with half-lives below one second ($^{33}$Ar: T$_{1/2}$ =174 ms). A mass accuracy of about $10^{-7}$ ($\delta m \approx 4$ keV) was achieved for all investigated nuclides. The isobaric multiplet mass equation (IMME) was checked for the $A=33$, $T=3/2$ quartet and found to be inconsistent with the generally accepted quadratic form