arXiv subjects

P. -M. Hillenbrand

Publications and source records attributed to P. -M. Hillenbrand.

At least 19 recordsLinked to original sources

arXiv2026

Rate coefficients for dielectronic recombination of N-like Ne

Dielectronic recombination (DR) for the process Ne$^{3+}$ + e$^{-}$ $\rightarrow$ Ne$^{2+}$ was investigated in a merged-beams arrangement at the heavy-ion storage ring CRYRING@ESR. The energy-dependent DR rate coefficient, $α(E)$ was measured over the electron-ion collision energy range from 0 to 25 eV. The measurements cover the complete set of DR resonance series associated with $2s\to2p$ core excitations. The primary ion beam is estimated to have consisted of $44\%$ of the ions in the ground state, with the remainder distributed among long-lived metastable levels. In addition to the measurements we carried out quantum mechanical calculations of DR cross sections. The theoretical treatment includes contributions from the ground and excited metastable initial levels, weighted according to the estimated beam composition. From the experimental energy-resolved spectra, we derive a temperature dependent DR plasma recombination rate coefficient $α_\mathrm{exp}(T)$ (PRRC). In the temperature domain where Ne$^{3+}$ is abundant in collisionally ionized plasmas, the present results show a good agreement with the present and with previous theoretical predictions. In the low-temperature regime characteristic for photoionized plasmas, the experimentally derived DR plasma rate coefficient is slightly larger than the published theoretical ones and does not agree within the experimental uncertainties. Parametrized fits of the experimentally derived DR PRRC are presented in order to facilitate an easy inclusion into astrophysical modelling codes.

physics.atom-ph↗

arXiv2025

Double to tenfold M-shell photoionization of singly charged lanthanum ions

Using the photon-ion merged-beams technique at the PETRA\,III synchrotron light source, we have measured cross sections for double and up to tenfold photoionization of La$^{+}$ ions by a single photon in the energy range 820--1400~eV, where resonances and thresholds occur that are associated with the excitation or ionization of one $M$-shell electron. These cross sections represent experimental benchmark data for the further development of quantum theoretical methods, which will have to provide the bulk of the atomic data required for the modeling of nonequilibrium plasmas such as kilonovae. In the present work, we have upgraded the Jena Atomic Calculator (JAC) and pushed the state-of-the-art of quantum calculations for heavy many-electron systems to new limits. In particular, we have performed large-scale calculations of the La$^+$ photoabsorption cross section and of the deexcitation cascades, which set in after the initial creation of a $3d$ hole. Our theoretical results largely agree with our experimental findings. However, our theoretical product-ion charge state distributions are somewhat narrower than the experimental ones, which is most probably due to the simplifications necessary to keep the cascade calculations tractable.

physics.atom-ph↗

arXiv2025

First Proton-Induced Cross Sections on a Stored Rare Ion Beam: Measurement of 118Te(p,γ) for Explosive Nucleosynthesis

We present the first nuclear cross-section measurements of (p,γ) and (p,n) reactions on 118Te at energies relevant for the γ-process nucleosynthesis. Absolute cross-section values for center-of-mass energies of 6, 7 and 10 MeV are provided, together with a theoretical extrapolation to the Gamow window. This experiment marks the first time that direct proton-induced reactions have been measured on a radioactive ion beam at the Experimental Storage Ring (ESR) at GSI, Darmstadt. This paves the way for a large variety of measurements, delivering new constraints for explosive nucleosynthesis and for physics beyond nuclear stability.

nucl-ex↗

arXiv2025

Testing strong-field QED to second-order in the highly correlated atomic system berylliumlike Pb78+ by electron-ion recombination spectroscopy

A low-energy storage ring with an ultracold electron cooler has been coupled with a heavy-ion accelerator facilitating high-resolution electron-ion collision spectroscopy of the heaviest few-electron ions. In the present work resonant electron-ion recombination of berylliumlike Pb$^{78+}$ ions was measured in the collision-energy range 9.3-16.5eV and a value of 244.937(30) eV is derived for the Pb$^{78+}$($2s^2\;^1S_0 - 2s\,2p\;^3P_1$) excitation energy. This result agrees with the most recent (less accurate) theoretical value of 244.942(52) eV [Malyshev et al., Physical Review A 110, 062824 (2024)], which has been calculated by applying strong-field QED rigorously up to the second order. The present investigation suggests that further technical improvements can potentially increase the experimental accuracy by an order of magnitude.

physics.atom-ph↗

arXiv2025

Bayesian and Monte Carlo approaches to estimating uncertainty for the measurement of the bound-state $β$ decay of $^{205}\mathrm{Tl}^{81+}$

The measurement of the bound-state $β$ decay of $^{205}\mathrm{Tl}^{81+}$ at the Experimental Storage Ring at GSI, Darmstadt, has recently been reported with substantial impact on the use of $^{205}\mathrm{Pb}$ as an early Solar System chronometer and the low-energy measurement of the solar neutrino spectrum via the LOREX project. Due to the technical challenges in producing a high-purity $^{205}\mathrm{Tl}^{81+}$ secondary beam, a robust statistical method needed to be developed to estimate the variation in the contaminant $^{205}\mathrm{Pb}^{81+}$ produced in the fragmentation reaction, which was subsequently transmitted and stored in the ESR. Here we show that Bayesian and Monte Carlo methods produced comparable estimates for the contaminant variation, each with unique advantages and challenges given the complex statistical problems for this experiment. We recommend the adoption of such methods in future experiments that exhibit unknown statistical fluctuations.

nucl-ex↗

arXiv2025

Half-life determination of heavy ions in a storage ring considering feeding and depleting background processes

Heavy-ion storage rings have relatively large momentum acceptance which allows for multiple ion species to circulate at the same time. This needs to be considered in radioactive decay measurements of highly charged ions, where atomic charge exchange reactions can significantly alter the intensities of parent and daughter ions. In this study, we investigate this effect using the decay curves of ion numbers in the recent $^{205}$Tl$^{81+}$ bound-state beta decay experiment conducted using the Experimental Storage Ring at GSI Darmstadt. To understand the intricate dynamics of ion numbers, we present a set of differential equations that account for various atomic and nuclear reaction processes-bound-state beta decay, atomic electron recombination and capture, and electron ionization. By incorporating appropriate boundary conditions, we develop a set of differential equations that accurately simulate the decay curves of various simultaneously stored ions in the storage ring: $^{205}$Tl$^{81+}$, $^{205}$Pb$^{81+}$, $^{205}$Pb$^{82+}$, $^{200}$Hg$^{79+}$, and $^{200}$Hg$^{80+}$. Through a quantitative comparison between simulations and experimental data, we provide insights into the detailed reaction mechanisms governing stored heavy ions within the storage ring. Our approach effectively models charge-changing processes, reduces the complexity of the experimental setup, and provides a simpler method for measuring the decay half-lives of highly charged ions in storage rings.

nucl-ex↗

arXiv2025

Bound-State Beta Decay of $\mathbf{\mathrm{^{205}{Tl}^{81+}}}$ Ions and the LOREX Project

Stable $^{205}$Tl ions have the lowest known energy threshold for capturing electron neutrinos ($ν_e$) of ${ E}_{ν_e}\ge50.6$\,keV. The Lorandite Experiment (LOREX), proposed in the 1980s, aims at obtaining the longtime averaged solar neutrino flux by utilizing natural deposits of Tl-bearing lorandite ores. To determine the $ν_e$ capture cross section, it is required to know the strength of the weak transition connecting the ground state of $^{205}$Tl and the 2.3 keV first excited state in $^{205}$Pb. The only way to experimentally address this transition is to measure the bound-state beta decay ($β_{b}$) of fully ionized $\mathrm{^{205}Tl^{81+}}$ ions. After three decades of meticulous preparation, the half-life of the $β_{b}$ decay of $\mathrm{^{205}Tl^{81+}}$ has been measured to be $291_{-27}^{+33}$ days using the Experimental Storage Ring (ESR) at GSI, Darmstadt. The longer measured half-life compared to theoretical estimates reduces the expected signal-to-noise ratio in the LOREX, thus challenging its feasibility.

nucl-ex↗

arXiv2025

Double-$K$-hole resonances in single photoionization of He-like B$^{3+}$ ions

Within a joint experimental and theoretical research project, single photoionization of He-like B$^{3+}$ ions was investigated in the energy range from approximately 250 to 1200~eV. With the parent-ion beam in the experiment containing both $1s^2~^1S$ ground-state and $1s2s~^3S$ metastable B$^{3+}$ ions, double-core-hole resonances could be studied. Two series of hollow resonant states were observed, one populated by $K$-shell double excitation $1s^2~^1S \to 2\ell n\ell'~^1P$ ($\ell=s,p$; $\ell'=p,s$; $n=2,3,..,6$) at photon energies up to about 510~eV, the other by $K$-shell single excitation $1s2s~^3S \to 2\ell n\ell'~^3P$ ($\ell=s,p$; $\ell'=p,s$; $n=2,3,..,6$) at energies up to about 310~eV. High resolving powers up to approximately 29000 were achieved. The relativistic many-body perturbation theory was employed to determine level-to-level cross sections for $K$-shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. The energy uncertainties of the most prominent resonances are estimated to be below $\pm 1$ meV. Convergent close coupling (CCC) calculations provided single-photoionization cross sections $σ_{34}$ for B$^{3+}$ including the resonant and non-resonant channels. Apart from the resonances, $σ_{34}$ is dominated by direct ionization in the investigated energy range. The contribution $σ_{34}^{\mathrm{dir}}$ of the latter process to $σ_{34}$ was separately determined by using the random-phase approximation with exchange and relativistic Hartree-Fock calculations which agree very well with previous calculations. Direct ionization of one electron accompanied by excitation of the remaining electron was treated by the CCC theory and found to be a minor contribution to $σ_{34}$.

physics.atom-ph↗

arXiv2024

High-temperature $^{205}$Tl decay clarifies $^{205}$Pb dating in early Solar System

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, $^{205}$Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars. However, making accurate abundance predictions for $^{205}$Pb has so far been impossible because the weak decay rates of $^{205}$Pb and $^{205}$Tl are very uncertain at stellar temperatures. To constrain these decay rates, we measured for the first time the bound-state $β^-$ decay of fully ionized $^{205}$Tl$^{81+}$, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate $^{205}$Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the $^{205}$Pb/$^{204}$Pb ratio from meteorites, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun's birth as a long-lived, giant molecular cloud and support the use of the $^{205}$Pb--$^{205}$Tl decay system as a chronometer in the early Solar System.

nucl-ex↗

arXiv2023

Storage, Accumulation and Deceleration of Secondary Beams for Nuclear Astrophysics

Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of $^{118}$Te$^{52+}$ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about $10^6$ ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.

physics.ins-det↗

arXiv2023

Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C$_2^-$

Carbon $1s$ core-hole excitation of the molecular anion C$_2^-$ has been experimentally studied at high resolution by employing the photon-ion merged-beams technique at a synchrotron light source. The experimental cross section for photo--double-detachment shows a pronounced vibrational structure associated with $1σ_u\to3σ_g$ and $1σ_g \to 1π_u$ core excitations of the C$_2^-$ ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C$_2^-$ molecular anion by 0.2~Å upon this core photoexcitation. The associated change of the molecule's moment of inertia leads to a noticeable rotational broadening of the observed vibrational spectral features. This broadening is accounted for in the present analysis which provides the spectroscopic parameters of the C$_2^-$ $1σ_u^{-1}\,3σ_g^2\;{^2}Σ_u^+$ and $1σ_g^{-1}\,3σ_g^2\;{^2}Σ_g^+$ core-excited levels.

physics.atom-ph↗

arXiv2022

Single and double $K$-shell vacancy production in slow Xe$^\textrm{54+,53+}$-Xe collisions

We present an experimental and theoretical study of symmetric $\textrm{Xe}^{54+}+\textrm{Xe}$ collisions at 50, 30, and 15 MeV/u, corresponding to strong perturbations with $v_K/v_\text{p}$ = 1.20, 1.55, and 2.20, respectively ($v_K$: classical $K$-shell orbital velocity, $v_\text{p}$: projectile velocity), as well as $\textrm{Xe}^{53+}+\textrm{Xe}$ collisions at 15 MeV/u. For each of these systems, x-ray spectra were measured under a forward angle of $35^\circ$ with respect to the projectile beam. Target satellite and hypersatellite radiation, $Kα_{2,1}^\mathrm{s}$ and $Kα_{2,1}^\mathrm{hs}$, respectively, were analyzed and used to derive cross section ratios for double-to-single target $K$-shell vacancy production. We compare our experimental results to relativistic time-dependent two-center calculations.

physics.atom-ph↗

arXiv2022

X-ray emission associated with radiative recombination for Pb$^{82+}$ ions at threshold energies

For bare lead ions, decelerated to the low beam energy of 10 MeV/u, the x-ray emission associated with radiative recombination (RR) at "cold collision" conditions has been studied at the electron cooler of CRYRING@ESR at GSI-Darmstadt. Utilizing dedicated x-ray detection chambers installed at 0° and 180° observation geometry, we observed for the very first time for stored ions the full x-ray emission spectrum associated with RR under electron cooling conditions. Most remarkably, no line distortion effects due to delayed emission are present in the well resolved spectra, spanning over a wide range of x-ray energies (from about 5 to 100 keV) which enable to identify fine-structure resolved Lyman, Balmer as well as Paschen x-ray lines along with the RR transitions into the K-, L and M-shell of the ions. To compare with theory, an elaborate theoretical model has been applied. By considering the relativistic atomic structure of Pb$^{81+}$, this model is based on a sophisticated computation of the initial population distribution via RR for all atomic levels up to Rydberg states with principal quantum number $n=$ 165 in combination with cascade calculations based on time-dependent rate equations. Within the statistical accuracy, the experimental x-ray line emission is in very good agreement with the results of the theoretical model applied. Most notably, this comparison sheds light on the contribution of prompt and delayed X-ray emission (up to 70 ns) to the observed X-ray spectra, originating in particular from Yrast transitions into inner shells.

physics.atom-ph↗

arXiv2021

Electronic structure effects in the electron bremsstrahlung from heavy ions

A fully relativistic approach is presented for the calculation of the bremsstrahlung emitted by an electron scattered off an ionic target. The ionic target is described as a combination of an effective Coulomb potential and a finite-range potential induced by the electronic cloud of the ion. The approach allows us to investigate the influence of the electronic structure of the target on the properties of the emitted radiation. We calculate the double differential cross-section and Stokes parameters of the bremsstrahlung of an electron scattered off uranium ions in different charge states, ranging from bare to neutral uranium. Results on the high-energy endpoint of the electron bremsstrahlung from Li-like uranium ions ${\rm U}^{89+}$ are compared to the recent experimental data. For this process, it is found that taking into account the electronic structure of the target results in modification of the cross-section on the level of 14%, which can, in principle, be seen in present-day experiments.

physics.atom-ph↗

arXiv2021

Electron-loss-to-continuum cusp in collisions of U$^{89+}$ with N$_{2}$ and Xe

We study the electron-loss-to-continuum (ELC) cusp experimentally and theoretically by comparing the ionization of U$^{89+}$ projectiles in collisions with N$_2$ and Xe targets, at a beam energy of 75.91 MeV/u. The coincidence measurement between the singly ionized projectile and the energy of the emitted electron is used to compare the shape of the ELC cusp at weak and strong perturbations. A significant energy shift for the centroid of the electron cusp is observed for the heavy target of Xe as compared to the light target of N$_2$. Our results provide a stringent test for fully relativistic calculations of double-differential cross sections performed in the first-order approximation and in the continuum-distorted-wave approach.

physics.atom-ph↗

arXiv2020

Determination of luminosity for in-ring reactions: A new approach for the low-energy domain

Luminosity is a measure of the colliding frequency between beam and target and it is a crucial parameter for the measurement of absolute values, such as reaction cross sections. In this paper, we make use of experimental data from the ESR storage ring to demonstrate that the luminosity can be precisely determined by modelling the measured Rutherford scattering distribution. The obtained results are in good agreement with an independent measurement based on the x-ray normalization method. Our new method provides an alternative way to precisely measure the luminosity in low-energy stored-beam configurations. This can be of great value in particular in dedicated low-energy storage rings where established methods are difficult or impossible to apply.

nucl-ex↗

arXiv2020

Electron capture of Xe$^{54+}$ in collisions with H${_2}$ molecules in the energy range between 5.5 MeV/u and 30.9 MeV/u

The electron capture process was studied for Xe$^{54+}$ colliding with H$_2$ molecules at the internal gas target of the ESR storage ring at GSI, Darmstadt. Cross section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogen-like ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 MeV/u and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron capture data was recorded at the intermediate and in particular the low collision energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data is found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.

physics.atom-ph↗

arXiv2019

New Test of Modulated Electron Capture Decay of Hydrogen-Like $^{142}$Pm Ions: Precision Measurement of Purely Exponential Decay

An experiment addressing electron capture (EC) decay of hydrogen-like $^{142}$Pm$^{60+}$ ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7) s$^{-1}$ for automatic analysis and 0.0141(7) s$^{-1}$ for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4).

nucl-ex↗