arXiv subjects

Klaus Wendt

Publications and source records attributed to Klaus Wendt.

13 recordsLinked to original sources

arXiv2026

Measurement of the O$^{-}$ Photodetachment cross-section in the electrostatic storage ring FLSR

The achievable precision of photodetachment studies via tunable laser light has been investigated on circulating oxygen anions at the room-temperature electrostatic low-energy storage ring of Frankfurt University (FLSR) in preparation of investigations on molecular species. For this purpose, the FLSR, originally designed for reaction dynamics studies on positive ions, was upgraded by a source for anions, by the installation of a tunable high repetition rate laser system and by implementation of a transversal interaction region between laser and ion beam. Results on the electron affinity and the ground state fine structure of O$^{-}$, which both serve as a calibration standard, are discussed, exhibiting the performance and accuracy of this new spectroscopic application of the FLSR.

physics.atom-ph↗

arXiv2026

Laser Spectroscopy of Thulium Isotopes Near the (N=82) Shell Closure: Nuclear Moment and Charge Radius of ${}^{152\mathrm{m}}\mathrm{Tm}$

We report on resonance ionization laser spectroscopy measurements performed on both neutron-deficient and neutron-rich thulium ($\mathrm{Tm}, Z=69$) isotopes. Isotope shifts were determined for three atomic ground-state transitions at wavelengths of $389.8\,\mathrm{nm}$, $388.4\,\mathrm{nm}$, and $388.8\,\mathrm{nm}$ in the isotopes ${}^{152\mathrm{m}}\mathrm{Tm}$, ${}^{153}\mathrm{Tm}$, ${}^{154\mathrm{m}}\mathrm{Tm}$, and ${}^{169}\mathrm{Tm}$. In addition, for the $389.8\,\mathrm{nm}$ transition, measurements were extended to the isotope ${}^{170}\mathrm{Tm}$, and the hyperfine structure was partially resolved for all five isotopes. For this transition, the isotope shift could be determined for one more isotope, ${}^{154\mathrm{m}}\mathrm{Tm}$. From the extracted hyperfine coupling constants, the nuclear magnetic dipole moment for ${}^{152\mathrm{m}}\mathrm{Tm}$ was determined for the first time, resulting in $\mu\left({}^{152\mathrm{m}}\mathrm{Tm}\right) = 5.8(3) \mu_\mathrm{N}$. Furthermore, the mean-square nuclear charge radius $\delta\langle r^2\rangle^{152\mathrm{m},169} = -1.86(25)\,\mathrm{fm}^2$ for ${}^{152\mathrm{m}}\mathrm{Tm}$ was extracted from the measured isotope shifts.

nucl-ex↗

arXiv2025

Improved limit on the effective electron neutrino mass with the ECHo-1k experiment

The effective electron neutrino mass can be determined by analyzing the endpoint region of the $^{163}$Ho electron capture spectrum, provided a measurement with high energy resolution and high statistics using calorimetric techniques. Here, the Electron Capture in $^{163}$Ho collaboration, ECHo, presents an analysis of the most precise $^{163}$Ho spectrum currently available, obtained with the ECHo-1k experiment and comprising about 200 million events. A very low background rate of $B=9.1(1.3)\times 10^{-6}$ /eV/pixel/day was achieved allowing for a reliable analysis of the endpoint region. The derived endpoint energy $Q = 2862(4)$ eV is in excellent agreement with the one independently determined via Penning-trap mass spectrometry of $Q=2863.2(6)$ eV [1]. The upper limit of the effective electron neutrino mass is improved by almost a factor 2 compared to the lowest current value [2], reaching $m_{ν_\mathrm{e}} < 15 $ eV/c${^2}$ (90\% credible interval).

hep-ex↗

arXiv2022

High-resolution laser system for the S3-Low Energy Branch

In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure data are presented for stable isotopes of these elements. The erbium isotopes were studied using the $4f^{12}6s^2$ $^3H_6 \rightarrow 4f^{12}(^3 H)6s6p$ $J = 5$ atomic transition (415 nm) and the tin isotopes were studied by the $5s^25p^2 (^3P_0) \rightarrow 5s^25p6s (^3P_1)$ atomic transition (286.4 nm), and are used as a benchmark of the laser setup. Additionally, the tin isotopes were studied by the $5s^25p6s (^3P_1) \rightarrow 5s^25p6p (^3P_2)$ atomic transition (811.6 nm), for which new isotope-shift data was obtained and the corresponding field-shift $F_{812}$ and mass-shift $M_{812}$ factors are presented.

nucl-ex↗

arXiv2020

Specific Heat of Holmium in Gold and Silver at Low Temperatures

The specific heat of dilute alloys of holmium in gold and in silver plays a major role in the optimization of low temperature microcalorimeters with enclosed $^{163}\textrm{Ho}$, such as the ones developed for the neutrino mass experiment ECHo. We investigate alloys with atomic concentrations of $x_\textrm{Ho}=0.01\,\% - 4\,\%$ at temperatures between $10\,\textrm{mK}$ and $800\,\textrm{mK}$. Due to the large total angular momentum $J=8$ and nuclear spin $I=7/2$ of $\textrm{Ho}^{3+}$ ions, the specific heat of $\underline{\textrm{Au}}\textrm{:Ho}$ and $\underline{\textrm{Ag}}\textrm{:Ho}$ depends on the detailed interplay of various interactions, including contributions from the localized 4f electrons and nuclear contributions via hyperfine splitting. This makes it difficult to accurately determine the specific heat of these materials numerically. Instead, we measure their specific heat by using three experimental set-ups optimized for different concentration and temperature ranges. The results from measurements on six holmium alloys demonstrate that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at $T\approx 250\,\textrm{mK}$, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. With regard to ECHo, we conclude that for typical operating temperatures of $T\leq 20\,\textrm{mK}$, silver holmium alloys with $x_\textrm{Ho}\gtrsim 1\,\%$ are suited best.

cond-mat.mtrl-sci↗

arXiv2020

Detection of missing low-lying atomic states in actinium

Two lowest-energy odd-parity atomic levels of actinium, 7s^27p 2P^o_1/2, 7s^27p 2P^o_3/2, were observed via two-step resonant laser-ionization spectroscopy and their respective energies were measured to be 7477.36(4) cm^-1 and 12 276.59(2) cm^-1. The lifetimes of these states were determined as 668(11) ns and 255(7) ns, respectively. In addition, these properties were calculated using a hybrid approach that combines configuration interaction and coupled-cluster methods in good agreement. The data are of relevance for understanding the complex atomic spectra of actinides and for developing efficient laser-cooling and ionization schemes for actinium, with possible applications for high-purity medicalisotope production and future fundamental physics experiments with this atom.

physics.atom-ph↗

arXiv2020

The electron affinity of astatine

One of the most important properties influencing the chemical behavior of an element is the energy released with the addition of an extra electron to the neutral atom, referred to as the electron affinity (EA). Among the remaining elements with unknown EA is astatine, the purely radioactive element 85. Astatine is the heaviest naturally occurring halogen and its isotope $^{211}$At is remarkably well suited for targeted radionuclide therapy of cancer. With the At$^-$ anion being involved in many aspects of current astatine labelling protocols, the knowledge of the electron affinity of this element is of prime importance. In addition, the EA can be used to deduce other concepts such as the electronegativity, thereby further improving the understanding of astatine's chemistry. Here, we report the first measurement of the EA for astatine to be 2.41578(7)eV. This result is compared to state-of-the-art relativistic quantum mechanical calculations, which require incorporation of the electron-electron correlation effects on the highest possible level. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements, which are produced at a one-atom-at-a-time rate.

physics.atom-ph↗

arXiv2019

Determination of measurement uncertainty by Monte Carlo simulation

Modern coordinate measurement machines (CMM) are universal tools to measure geometric features of complex three-dimensional workpieces. To use them as reliable means of quality control, the suitability of the device for the specific measurement task has to be proven. Therefore, the ISO 14253 standard requires, knowledge of the measurement uncertainty and, that it is in reasonable relation with the specified tolerances. Hence, the determination of the measurement uncertainty, which is a complex and also costly task, is of utmost importance. The measurement uncertainty is usually influenced by several contributions of various sources. Among those of the machine itself, e.g., guideway errors and the influence of the probe and styli play an important role. Furthermore, several properties of the workpiece, such as its form deviations and surface roughness, have to be considered. Also the environmental conditions, i.e., temperature and its gradients, pressure, relative humidity and others contribute to the overall measurement uncertainty. Currently, there are different approaches to determine task-specific measurement uncertainties. This work reports on recent advancements extending the well-established method of PTB's Virtual Coordinate Measuring Machine (VCMM) to suit present-day needs in industrial applications. The VCMM utilizes numerical simulations to determine the task-specific measurement uncertainty incorporating broad knowledge about the contributions of, e.g., the used CMM, the environment and the workpiece.

physics.ins-det↗

arXiv2019

Highly efficient isotope separation and ion implantation of $^{163}$Ho for the ECHo project

The effective electron neutrino mass measurement at the ECHo experiment requires high purity $^{163}$Ho, which is ion implanted into detector absorbers. To meet the project specifications in efficiency and purity, the entire process chain of ionization, isotope separation, and implantation of $^{163}$Ho was optimized. A new two-step resonant laser ionization scheme was established at the $30\, kV$ magnetic mass separator RISIKO. This achieved ionization and separation efficiencies with an average of $69(5)_\textrm{stat}(4)_\textrm{sys}\,\%$ using intra-cavity frequency doubled Ti:sapphire lasers. The implantation of a $^{166\textrm{m}}$Ho impurity is suppressed about five orders of magnitude by the mass separation. A dedicated implantation stage with focusing and scanning capability enhances the geometric implantation efficiency into the ECHo detectors to $20(2)\,\%$.

physics.acc-ph↗

arXiv2018

Optimization of a laser ion source for $^{163}$Ho isotope separation

To measure the mass of the electron neutrino, the "Electron Capture in Holmium-163" (ECHo) collaboration aims at calorimetrically measuring the spectrum following electron capture in $^{163}$Ho. The success of the ECHo experiment depends critically on the radiochemical purity of the $^{163}$Ho sample, which is ion-implanted into the calorimeters. For this, a $30 \, \textrm{kV}$ high transmission magnetic mass separator equipped with a resonance ionization laser ion source is used. To meet the ECHo requirements, the ion source unit was optimized with respect to its thermal characteristics and material composition by means of finite element method (FEM) thermal-electric calculations and chemical equilibrium simulation using the Gibbs energy minimization method. The new setup provides a much improved selectivity in laser ionization versus interfering surface ionization of $2700(500)$ and a superior overall efficiency of $41(5) \, \textrm{%}$ for the ion-implantation process.

physics.ins-det↗

arXiv2018

Laser spectroscopy of the 1001nm ground state transition in dysprosium

We present the first direct excitation of the presumably ultra-narrow $1001 \, \textrm{nm}$ ground state transition in atomic dysproium. By using resonance ionization spectroscopy with pulsed Ti:sapphire lasers at a hot cavity laser ion source, we were able to measure the isotopic shifts in the $1001 \, \textrm{nm}$ line between all seven stable isotopes. Furthermore, we determined the upper level energy from the atomic transition frequency of the $^{164} \textrm{Dy}$ isotope as $9991.004(1) \, \textrm{cm}^{-1}$ and confirm the level energy listed in the NIST database. Since a sufficiently narrow natural linewidth is an essential prerequisite for high precision spectroscopic investigations for fundamental questions we furthermore determined a lower limit of $2.9(1) \, μ\textrm{s}$ for the lifetime of the excited state.

physics.atom-ph↗

arXiv2017

Efficient and robust photo-ionization loading of beryllium ions

We demonstrate the efficient generation of Be$^+$ ions with a 60 ns and 150 nJ laser pulse near 235 nm for two-step photo-ionization, proven by subsequent counting the number of ions loaded into a linear Paul trap. The bandwidth and power of the laser pulse are chosen in such a way that a first, resonant step fully saturates the entire velocity distribution of beryllium atoms effusing from a thermal oven. The second excitation step is driven by the same light field causing efficient non-resonant ionization. Our ion-loading scheme is more than 15 times more efficient as compared to former pathways using two-photon continuous wave laser excitation.

physics.atom-ph↗

arXiv2011

Resonance ionization spectroscopy of thorium isotopes - towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of Th-229

In-source resonance ionization spectroscopy was used to identify an efficient and selective three step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in preparation of laser spectroscopic investigations for an identification of the low-lying Th-229m isomer predicted at 7.6 +- 0.5 eV above the nuclear ground state. Using a sample of Th-232, a multitude of optical transitions leading to over 20 previously unknown intermediate states of even parity as well as numerous high-lying odd parity auto-ionizing states were identified. Level energies were determined with an accuracy of 0.06 cm-1 for intermediate and 0.15 cm-1 for auto-ionizing states. Using different excitation pathways an assignment of total angular momenta for several energy levels was possible. One particularly efficient ionization scheme of thorium, exhibiting saturation in all three optical transitions, was studied in detail. For all three levels in this scheme, the isotope shifts of the isotopes Th-228, Th-229, and Th-230 relative to Th-232 were measured. An overall efficiency including ionization, transport and detection of 0.6 was determined, which was predominantly limited by the transmission of the mass spectrometer ion optics.

physics.atom-ph↗