Corrosion and tribocorrosion of hafnium in simulated body fluids.

Hafnium is a passive metal with good biocompatibility and osteogenesis, however, little is known about its resistance to wear and corrosion in biological environments. The corrosion and tribocorrosion behavior of hafnium and commercially pure (CP) titanium in simulated body fluids were investigated using electrochemical techniques. Cyclic polarization scans and open circuit potential measurements were performed in 0.9% NaCl solution and 25% bovine calf serum solution to assess the effect of organic species on the corrosion behavior of the metal. A pin-on-plate configuration tribometer and a three electrode electrochemical cell were integrated to investigate the tribocorrosion performance of the studied materials. The results showed that hafnium has good corrosion resistance. The corrosion density currents measured in its passive state were lower than those measured in the case of CP titanium; however, it showed a higher tendency to suffer from localized corrosion, which was more acute when imperfections were present on the surface. The electrochemical breakdown of the oxide layer was retarded in the presence of proteins. Tribocorrosion tests showed that hafnium has the ability to quickly repassivate after the oxide layer was damaged; however, it showed higher volumetric loss than CP titanium in equivalent wear-corrosion conditions

High-precision laser spectroscopy of helium-like carbon 12C4+

The size of an atomic nucleus is a fundamental observable and defined by the distribution of the neutrons and protons composing the nucleus and the respective mean-square radii. The precise investigation of the nuclear size across the chart of nuclides delivers important benchmarks for nuclear structure theory and tests our fundamental knowledge of matter. In contrast to matter and neutron radii, the nuclear charge radius can be probed through the well-known electromagnetic interaction. Different techniques have been developed over time to measure nuclear charge radii such as elastic electron scattering or muonic atom spectroscopy. While these techniques are typically limited to stable nuclei, collinear laser spectroscopy and resonant ionization spectroscopy are used to determine nuclear charge radii of short-lived radioactive isotopes relative to a reference charge radius of a stable isotope. In some cases, this can limit the uncertainty of the obtained charge radii of radioactive nuclei to the uncertainty of the reference measurements from elastic electron scattering or muonic atom spectroscopy. To overcome this limit in light mass nuclei like 10, 11B, an all-optical approach for the charge radius determination purely from laser spectroscopy measurements and non-relativistic QED calculations was tested in this work with the well-known nucleus of 12C through laser excitation of helium-like 12C4+ from the metastable 1s2s 3S1 state with a lifetime of 21 ms to the 1s2p 3PJ states. The high-precision collinear laser spectroscopy was performed at the Collinear Apparatus for Laser Spectroscopy and Applied Science (COALA), situated at the Institute for Nuclear Physics at the Technical University Darmstadt. In order to produce the the highly charged C4+ ions, a new electron beam ion source including a Wien filter for charge/mass separation was installed and commissioned at COALA. Additionally, a new switchyard and beam diagnostics were designed, built and installed. The 1s2s 3S1 → 1s2p 3PJ rest-frame transition frequencies were determined with less than 2 MHz uncertainty through quasi-simultaneous collinear and anticollinear laser spectroscopy. These transition frequencies are in excellent agreement with state-of-the-art ab initio atomic structure calculations and an all-optical nuclear charge radius of 12C was extracted. Its accuracy is limited by theory, which must be improved by two orders of magnitude before the experimental uncertainty becomes significant again. At that point, the accuracy of the extracted charge radius would have already outperformed all previous measurements of this observable. Furthermore, the high precision of this work enabled the estimation of the next missing order in the atomic structure calculations and the transition frequencies from this work can be used together with ongoing measurements in 13C4+ for a conventional determination of the mean-square charge radius difference δ⟨r2⟩12,13 between 12C and 13C which has not been measured so far by laser spectroscopy

Collinear laser spectroscopy of highly charged ions produced with an electron beam ion source

Collinear laser spectroscopy has been performed on He-like C$^{4+}$ ions extracted from an electron beam ion source (EBIS). In order to determine the transition frequency with the highest-possible accuracy, the lineshape of the fluorescence response function was studied for pulsed and continuous ion extraction modes of the EBIS in order to optimize its symmetry and linewidth. We found that the best signal-to-noise ratio is obtained using the continuous beam mode for ion extraction. Applying frequency-comb-referenced collinear and anticollinear laser spectroscopy, we achieved a measurement accuracy of better than 2\,MHz including statistical and systematic uncertainties. The origin and size of systematic uncertainties, as well as further applications for other isotopes and elements are discussed

Collinear Laser Spectroscopy of 2 3 ⁣S1→2 3 ⁣P ⁣J2\,{}^3\!S_1 \rightarrow 2\,{}^3\!P_{\!J} transitions in helium-like 12C4+^{12}\mathrm{C}^{4+}

Transition frequencies and fine-structure splittings of the $2\,{}^3\!S_1 \rightarrow 2\,{}^3\!P_{\!J}$ transitions in helium-like $^{12}\mathrm{C}^{4+}$ were measured by collinear laser spectroscopy on a 1-ppb level. Accuracy is increased by more than three orders of magnitude with respect to previous measurements, enabling tests of recent non-relativistic QED calculations including terms up to $m\alpha^7$. Deviations between the theoretical and experimental values are within theoretical uncertainties and are ascribed to $m\alpha^8$ and higher-order contributions in the series expansion of the NR-QED calculations. Finally, prospects for an all-optical charge radius determination of light isotopes are evaluated

On the performance of wavelength meters: Part 2 — frequency-comb based characterization for more accurate absolute wavelength determinations

Wavelength meters are widely used for frequency determinations and stabilization purposes since they cover a large wavelength range, provide a high read-out rate and have specified accuracies of up to 10⁻⁸. More accurate optical frequency measurements can be achieved with frequency combs but only at the price of considerably higher costs and complexity. In the context of precise and accurate frequency determinations for high-resolution laser spectroscopy, the performance of five different wavelength meters was quantified with respect to a frequency comb. The relative precision as well as the absolute accuracy has been investigated in detail, allowing us to give a sophisticated uncertainty margin for the individual instruments. We encountered a prominent substructure on the deviation between both device types with an amplitude of a few MHz that is repeating on the GHz scale. This finally limits the precision of laser scans which are monitored and controlled with wavelength meters. While quantifying its uncertainty margins, we found a high temporal stability in the characteristics of the wavelength meters which enables the preparation of wavelength-dependent adjustment curves for wide- and short-ranged scans. With this method, the absolute accuracy of wavelength meters can be raised up to the MHz level independently from the wavelength of the reference laser used for calibrating the device. Since this technique can be universally applied, it can lead to benefits in all fields of wavelength meter applications

The nuclear charge radius of ¹³C

The size is a key property of a nucleus. Accurate nuclear radii are extracted from elastic electron scattering, laser spectroscopy, and muonic atom spectroscopy. The results are not always compatible, as the proton-radius puzzle has shown most dramatically. Beyond helium, precision data from muonic and electronic sources are scarce in the light-mass region. The stable isotopes of carbon are an exception. We present a laser spectroscopic measurement of the root-mean-square (rms) charge radius of ¹³C and compare this with ab initio nuclear structure calculations. Measuring all hyperfine components of the 2³S → 2³P fine-structure triplet in ¹³C⁴⁺ ions referenced to a frequency comb allows us to determine its center-of-gravity with accuracy better than 2 MHz although second-order hyperfine-structure effects shift individual lines by several GHz. We improved the uncertainty of Rc(¹³C) determined with electrons by a factor of 6 and found a 3σ discrepancy with the muonic atom result of similar accuracy

Collinear Laser Spectroscopy of Helium-like ¹¹B³⁺

Collinear laser spectroscopy in the 1s2s³S₁→1s2p³P₀,₂ transitions of helium-like ¹¹B³⁺ was performed using the HITRAP beamline at the GSI Helmholtz Centre. The ions were produced in an electron beam ion source, extracted, and accelerated to a beam energy of 4 keV/q. Results agree with previous measurements within uncertainty. Thus, it was demonstrated that the metastable state in He-like ions is sufficiently populated to carry out collinear laser spectroscopy. The measurement is a pilot experiment for a series of measurements that will be performed at a dedicated collinear laser spectroscopy setup at TU Darmstadt with light helium-like ions

Radiative lifetime of the A 2{\Pi}1/2 state in RaF with relevance to laser cooling

The radiative lifetime of the $A$ $^2 \Pi_{1/2}$ (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate $\Gamma = 2.86(8) \times 10^7$ $s^{-1}$ are of relevance to the laser cooling of RaF via the optically closed $A$ $^2 \Pi_{1/2} \leftarrow X$ $^2\Sigma_{1/2}$ transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just 3 cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3) ns, in agreement with literature.Comment: Accepted as a Letter in Physical Review A; 8 pages of main text, 5 pages of supplemental materia

Nuclear charge radius of 26m^{26m}Al and its implication for Vud_{ud} in the quark-mixing matrix

Collinear laser spectroscopy was performed on the isomer of the aluminium isotope $^{26m}$Al. The measured isotope shift to $^{27}$Al in the $3s^{2}3p\;^{2}\!P^\circ_{3/2} \rightarrow 3s^{2}4s\;^{2}\!S_{1/2}$ atomic transition enabled the first experimental determination of the nuclear charge radius of $^{26m}$Al, resulting in $R_c$=\qty{3.130\pm.015}{\femto\meter}. This differs by 4.5 standard deviations from the extrapolated value used to calculate the isospin-symmetry breaking corrections in the superallowed $\beta$ decay of $^{26m}$Al. Its corrected $\mathcal{F}t$ value, important for the estimation of $V_{ud}$ in the CKM matrix, is thus shifted by one standard deviation to \qty{3071.4\pm1.0}{\second}.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let