G. Gwinner

The on-line charge breeding program at TRIUMF's Ion Trap For Atomic and Nuclear Science for precision mass measurements

TRIUMFs Ion Trap for Atomic and Nuclear science (TITAN) constitutes the only high precision mass measurement setup coupled to a rare isotope facility capable of increasing the charge state of short-lived nuclides prior to the actual mass determination in a Penning trap. Recent developments around TITANs charge breeder, the electron beam ion trap, form the basis for several successful experiments on radioactive isotopes with half-lives as low as 65 ms and in charge states as high as 22+.

First Use of High Charge States for Mass Measurements of Short-lived Nuclides in a Penning Trap

Penning trap mass measurements of short-lived nuclides have been performed for the first time with highly charged ions, using the TITAN facility at TRIUMF. Compared to singly charged ions, this provides an improvement in experimental precision that scales with the charge state q. Neutron-deficient Rb isotopes have been charge bred in an electron beam ion trap to q=8-12+ prior to injection into the Penning trap. In combination with the Ramsey excitation scheme, this unique setup creating low energy, highly charged ions at a radioactive beam facility opens the door to unrivaled precision with gains of 1-2 orders of magnitude. The method is particularly suited for short-lived nuclides such as the superallowed β emitter 74Rb (T(1/2)=65  ms). The determination of its atomic mass and an improved Q(EC) value are presented.

Storage ring measurement of the C IV recombination rate coefficient

The low-energy C IV dielectronic recombination (DR) rate coefficient associated with 2s → 2p Δn = 0 excitations of this lithium-like ion has been measured with high-energy resolution at the heavy-ion storage ring TSR of the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detection probabilities for the high Rydberg states produced by the recombination of this ion are discussed in detail. From the experimental data a Maxwellian plasma rate coefficient is derived with ±15% systematic uncertainty and parameterized for ready use in plasma-modeling codes. Our experimental result especially benchmarks the plasma rate coefficient below 104 K where DR occurs predominantly via C III (1s22p4l) intermediate states and where existing theories differ by orders of magnitude. Furthermore, we find that, to within our systematic uncertainty of 15%, the total dielectronic and radiative C IV recombination can be represented by the incoherent sum of our DR rate coefficient and the radiative recombination rate coefficient of Pequignot and coworkers.

Standard model tests with trapped radioactive atoms

We review the use of laser cooling and trapping for Standard Model tests, focusing on trapping of radioactive isotopes. Experiments with neutral atoms trapped using modern laser-cooling techniques are testing several basic predictions of electroweak unification. For nuclear β decay, demonstrated trap techniques include neutrino momentum measurements from beta-recoil coincidences, along with methods to produce highly polarized samples. These techniques have set the best general constraints on non-Standard Model scalar interactions in the first generation of particles. They also have the promise to test whether parity symmetry is maximally violated, to search for tensor interactions, and to search for new sources of time-reversal violation. There are also possibilities for exotic particle searches. Measurements of the strength of the weak neutral current can be assisted by precision atomic experiments using traps loaded with small numbers of radioactive atoms, and sensitivity to possible time-reversal violating electric dipole moments can be improved.

Dielectronic recombination (via N=2 -> N '=2 core excitations) and radiative recombination of Fe XX: Laboratory measurements and theoretical calculations

We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe xx forming Fe xix via N ¼ 2 ! N 0 ¼ 2( DN ¼ 0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF), and R-matrix methods, four different state-ofthe-art theoretical techniques. On average the theoretical resonance strengths agree to within .10% with experiment. The AUTOSTRUCTURE, MCDF, and R-matrix results are in better agreement with experiment than are the HULLAC results. However, in all cases the 1 � standard deviation for the ratios of the theoretical-to-experimental resonance strengths is &30%, which is significantly larger than the estimated relative experimental uncertainty of .10%. This suggests that similar errors exist in the calculated level populations and line emission spectrum of the recombined ion. We confirm that theoretical methods based on inverse-photoionization calculations (e.g., undamped R-matrix methods) will severely overestimate the strength of the DR process unless they include the effects of radiation damping. We also find that the coupling between the DR and radiative recombination (RR) channels is small. Below 2 eV the theoretical resonance energies can be up to � 30% larger than experiment. This is larger than the estimated uncertainty in the experimental energy scale (.0.5% below � 25 eV and .0.2% for higher energies) and is attributed to uncertainties in the calculations. These discrepancies makes DR of Fe xx an excellent case for testing atomic structure calculations of ions with partially filled shells. Above 2 eV, agreement between the theoretical and measured energies improves dramatically with the AUTOSTRUCTURE and MCDF results falling within 2% of experiment, the R-matrix results within 3%, and HULLAC within 5%. Agreement for all four calculations improves as the resonance energy increases. We have used our experimental and theoretical results to produce Maxwellian-averaged rate coefficients for DN ¼ 0D R of Fexx. For kBTe & 1 eV, which includes the predicted formation temperatures for Fe xx in an optically thin, low-density photoionized plasma with cosmic abundances, the experimental and theoretical results agree to better than � 15%. This is within the total estimated experimental uncertainty limits of .20%. Agreement below � 1 eV is difficult to quantify due to current theoretical and experimental limitations. Agreement with previously published LS-coupling rate coefficients is poor, particularly for kBTe . 80 eV. This is attributed to errors in the resonance energies of these calculations as well as the omission of DR via 2p1=2 ! 2p3=2 core excitations. We have also used our R-matrix results, topped off using AUTOSTRUCTURE for RR into J � 25 levels, to calculate the rate coefficient for RR of Fe xx. Our RR results are in good agreement with previously published calculations. We find that for temperatures as low as kBTe � 10 � 3 eV, DR still dominates over RR for this system. Subject headings: atomic data — atomic processes — methods: laboratory On-line material: machine-readable tables

M1/E2/M2 decay rates in Fe VII, Fe IX, Fe X and Fe XIII measured using a heavy-ion storage ring

Lifetimes (the inverse of the total decay rates) of several 3p and 3d levels in Ca-, Ar-, Cl- and Si-like ions of Fe that decay only by electric-dipole-forbidden transitions have been measured optically using a heavy-ion storage ring, observing either near-UV or EUV light. In several cases, more than one decay contributes to a given decay curve, which complicates the analysis. The lifetime results, with a precision ranging from 0.8 to 10%, compare well with some theoretical predictions.

Recombination in electron coolers

Abstract An introduction to electron–ion recombination processes is given and recent measurements are described as examples, focusing on low collision energies. Discussed in particular are fine-structure-mediated dielectronic recombination of fluorine-like ions, the moderate recombination enhancement by factors of typically 1.5–4 found for most ion species at relative electron–ion energies below about 10 meV, and the much larger enhancement occurring for specific highly charged ions of complex electronic structure, apparently caused by low-energy dielectronic recombination resonances. Recent experiments revealing dielectronic resonances with very large natural width are also described.

Penning-trap mass spectrometry of highly charged, neutron-rich Rb and Sr isotopes in the vicinity of A≈100

The neutron-rich mass region around A � 100 presents challenges for modeling the astrophysical r-process because of rapid shape transitions. We report on mass measurements using the TITAN Penning trap at TRIUMF-ISAC to attain more reliable theoretical predictions of r-process nucleosynthesis paths in this region. A new approach using highly charged (q = 15+) ions has been applied which considerably saves measurement time and preserves accuracy. New mass measurements of neutron-rich 94,97,98 Rb and 94,97 99 Sr have uncertainties of less than 4 keV and show deviations of up to 11� to previous measurements. An analysis using a parameterized r-process model is performed and shows that mass uncertainties for the A = 90 abundance region are eliminated.

Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory

Absolute total electron-ion recombination rate coefficients of argonlike Sc 3 + (3s 2 3p 6 ) ions have been measured for relative energies between electrons and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic recombination resonances attached to 3p → 3d and 3p→4s excitations. A broad resonance with an experimental width of 0.89′0.07 eV due to the 3p 5 3d 2 2 F intermediate state is found at 12.31′0.03 eV with a small experimental evidence for an asymmetric line shape. From R-matrix and perturbative calculations we infer that the asymmetric line shape may not only be due to quantum-mechanical interference between direct and resonant recombination channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but may be partly also due to the interaction with an adjacent overlapping dielectronic recombination resonance of the same symmetry. The overall agreement between theory and experiment is poor. Differences between our experimental and our theoretical resonance positions are as large as 1.4 eV. This illustrates the difficulty to accurately describe the structure of an atomic system with an open 3d shell with state-of-the-art theoretical methods. Furthermore, we find that a relativistic theoretical treatment of the system under study is mandatory since the existence of experimentally observed strong 3p 5 3d 2 2D and 3p 5 3d4s 2 D resonances can only be explained when calculations beyond LS coupling are carried out.

Dielectronic recombination of lithiumlike Ni 2 5 + ions: High-resolution rate coefficients and influence of external crossed electric and magnetic fields

Absolute dielectronic recombination (DR) rates for lithiumlike