In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic Kα radiation following the K → L excitation of He-like uranium. We pay special attention to the magnetic sub-level population of the excited 1s2lj states, which is directly related to the angular distribution of the characteristic Kα radiation. We show that the experimental data can be well described by calculations taking into account the excitation by the target nucleus as well as by the target electrons. Moreover, we demonstrate for the first time an important influence of the electron-impact excitation process on the angular distributions of the Kα radiation produced by excitation of He-like uranium in collisions with different targets.

PURPOSE:The first purpose of this phantom study was to verify whether a contrast-to-noise ratio (CNR)-driven exposure control (CEC) can maintain target CNR in angiography more precisely compared to a conventional detector dose-driven exposure control (DEC). The second purpose was to estimate the difference between incident air kerma produced by CEC and DEC when both exposure controls reach the same CNR. METHODS:A standardized 3D-printed phantom with an iron foil and a cavity, filled with iodinated contrast material, was developed to measure CNR using different image acquisition settings. This phantom was placed into a stack of polymethylmethacrylate and aluminum plates, simulating a patient equivalent thickness (PET) of 2.5-40 cm. Images were acquired using fluoroscopy and digital radiography modes with CEC using one image quality level and four image quality gradients and DEC having three different detector dose levels. The spatial frequency weighted CNR and incident air kerma were determined. The differences in incident air kerma between DEC and CEC were estimated. RESULTS:When using DEC, CNR decreased continuously with increasing attenuation, while CEC within physical limits maintained a predefined CNR level. Furthermore, CEC could be parameterized to deliver the CNR as a predefined function of PET. To provide a given CNR level, CEC used equal or lower air kerma than DEC. The mean estimated incident air kerma of CEC compared to DEC was between 3% (PET 20 cm) and 40% (PET 27.5 cm) lower in fluoroscopy and between 1% (PET 20 cm) and 55% (PET 2.5 cm) lower in digital radiography while maintaining CNR. CONCLUSION:Within physical and legislative limits, the CEC allows for a flexible adjustment of the CNR as a function of PET. Thus, the CEC enables task-dependent examination protocols with predefined image quality in order to easier achieve the as low as reasonably achievable principle. CEC required equal or lower incident air kerma than DEC to provide similar CNR, which allows for a substantial reduction of skin radiation dose in these situations.

We have studied the K-shell excitation of He-like uranium (U90+) in relativistic collisions with hydrogen and argon atoms. Performing measurements with different targets, as well as with different collision energies, enabled us to explore the proton- (nucleus-) impact excitation as well as the electron-impact excitation process for the heaviest He-like ion. The large fine-structure splitting in uranium allowed us to partially resolve excitation into different L-shell levels. State-of-the-art relativistic calculations which include excitation mechanisms due to the interaction with both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the electron-impact excitation process.

We present a systematic measurement of the X-ray emission asymmetries in the K-shell dielectronic, trielectronic, and quadruelectronic recombination of free electrons into highly charged ions. Iron ions in He-like through O-like charge states were produced in an electron beam ion trap, and the electron-ion collision energy was scanned over the recombination resonances. Two identical X-ray detectors mounted head-on and side-on with respect to the electron beam propagation recorded X-rays emitted in the decay of resonantly populated states. The degrees of linear polarization of X-rays inferred from observed emission asymmetries benchmark distorted-wave predictions of the Flexible Atomic Code (FAC) for several dielectronic recombination satellite lines. The present method also demonstrates its applicability for diagnostics of energy and direction of electron beams inside hot anisotropic plasmas. Both experimental and theoretical data can be used for modeling of hot astrophysical and fusion plasmas.

Parity non-conservation (PNC) had been at first theoretically proposed by Lee and Yang in 1956 in order to find a way out of the so–called “τ −γ puzzle” [1, 2]. The next year, Wu and collaborators observed an asymmetry in nuclear beta decay ascribed to parity non-conservation in weak processes [3], and, subsequently, Lee and Yang have been forthwith awarded with the Nobel Prize. Many later experiments in nuclear and high energy physics confirmed parity violation in weak interactions and precisely recorded weak charge and other related parameters [4–7]. Although with some initial controversies, the “τ − γ puzzle” was also solved out by understanding that both τ and γ were two decay channels of the same parent particle, known today as the charged kaon K [8, 9]. In contrast to nuclear and high energy physics, fewer experiments have been carried out in atomic physics to measure weak interaction’s properties. In fact, the conflicting results of the early Bismuth experiments in the ’70 [10–13] spread the conviction that nothing fundamentally useful could have ever been extracted from atomic physics experiments. Nonetheless, renewed interest on the subject rose again in the late ’80 and ’90 and led to the successful measurements of the weak charge Qw and related parameters in atomic Cesium [14–19], Thallium [20], Lead [21] and Ytterium [22]. On the theoretical side, starting from the early work of Curtis-Michel [23], several investigations of PNC have been made in the context of neutral atoms [24], few–electron ions [25, 26] and muonic atoms [27, 28]. In all the proposed studies, the little role played by PNC effects together with the need of precise measurements have been highlighted.

The design of a high-resolution asymmetric von Hamos spectrometer for low energy X-ray spectroscopy experiments at the electron cooler of CRYRING [1] in the international Facility for Antiproton and Ion Research (FAIR) in Darmstadt is presented in this document. The spectrometer will allow to measure, with a high resolution of down to 100 meV, the low-energy X-rays (5-10 keV) from radiative recombination (RR) of stored bare or few-electron heavy ions interacting with cooling electrons. X-ray tracing simulations show that the energies of the X-ray transitions can be measured with relative precision of a few ppm, which gives access to study the QED effects for mid-Z bare ions with a high precision. For these ions the nuclear size effect is much smaller than one-loop QED corrections. The proposed asymmetric von Hamos spectrometer benefits from the unique features of RR X-ray emission in the electron cooler of CRYRING, namely, the extremely long-linear (∼ 1 m x 1 mm) X-ray source accepted by von Hamos geometry and very cold electron beam temperature of about meV. This is achieved by application of adiabatic magnetic expansion of the electron beam, which increases substantially the intensities of RR X-rays and, consequently, the precision of determination of X-ray energies. In order to control the Doppler effect, two copies of the asymmetric von Hamos spectrometer will be installed next to the dipole magnets on both sides of the electron cooler to detect blue/red (0◦/180◦) shifted RR X-rays, what allows to eliminate completely the influence of Doppler effect on measured X-ray energies. The X-rays diffracted by the cylindrically bent crystal will be measured by a novel type of position sensitive semiconductor detector having nanoseconds time resolution, what will be crucial to eliminate non-RR X-ray background by counting photon-downcharged-ion coincidences. The spectrometers will be mounted to the dedicated intermediate vacuum chambers on the e-cooler axis. EDMS 2384915 v.LATEST status In Work access Public GSI_TDR_VonHamos_CRYRING_online.pdf modified 2020-06-15 13:00

We report a measurement of $KLL$ dielectronic recombination in charge states from Kr$^{+34}$ through Kr$^{+28}$, in order to investigate the contribution of Breit interaction for a wide range of resonant states. Highly charged Kr ions were produced in an electron beam ion trap, while the electron-ion collision energy was scanned over a range of dielectronic recombination resonances. The subsequent $K\alpha$ x rays were recorded both along and perpendicular to the electron beam axis, which allowed the observation of the influence of Breit interaction on the angular distribution of the x rays. Experimental results are in good agreement with distorted-wave calculations. We demonstrate, both theoretically and experimentally, that there is a strong state-selective influence of the Breit interaction that can be traced back to the angular and radial properties of the wavefunctions in the dielectronic capture.

We report the first systematic measurement of x-ray angular distribution and polarization following dielectronic, trielectronic and quadroelectronic recombination into He-like through O-like iron and krypton ions. The experimental data revealed that the the degree of polarization of x rays is dominated by relativistic Breit interaction and hitherto neglected higher-order trielectronic and quadroelectronic recombination resonances.

In this study, we investigated the potential of the Geant4 Monte Carlo simulation package for retrieving accurate elemental concentrations from energy dispersive X-ray fluorescence spectra. For this purpose, we implemented a Geant4 code that simulates an energy dispersive X-ray fluorescence spectrometer in a triaxial geometry. In parallel, we also performed measurements in a spectrometer with the same geometry, for validation of the present code. This spectrometer allows low limits of detection and permits an effective comparison of elemental concentrations down to tens of part-per-million. Several standard reference materials of both light, medium and heavy matrices were employed in order to attest the validity of simulations for several values of averaged atomic number. We observed good agreement of better than 25% for most fluorescence lines of interest, and for all materials. Discrepancies were observed at the multiple Compton scattering tail. We thus concluded from this experimental and theoretical study that the present Geant4 code can be incorporated in a quantitative method for the determination of trace elements in a triaxial-type spectrometer.

We studied angular distributions of x rays emitted in resonant recombination of highly charged iron and krypton ions, resolving dielectronic, trielectronic, and quadruelectronic channels. A tunable electron beam drove these processes, inducing x rays registered by two detectors mounted along and perpendicular to the beam axis. The measured emission asymmetries comprehensively benchmarked full-order atomic calculations. We conclude that accurate polarization diagnostics of hot plasmas can only be obtained under the premise of inclusion of higher-order processes that were neglected in earlier work.

We have studied the beta decay of the T-z = -1, f(7/2) shell nuclei Ni-54, Fe-50, Cr-46, and Ti-42 produced in fragmentation reactions. The proton separation energies in the daughter T-z = 0 nuclei are relatively large (approximate to 4-5 MeV) so studies of the. rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision beta-decay half-lives, excitation energies, and beta branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these beta decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths observed in beta decay including a sensitivity limit with the strengths of the T-z = +1 to T-z = 0 transitions derived from high resolution (He-3,t) reactions on the mirror target nuclei at RCNP, Osaka. The accumulated B(GT) strength obtained from both experiments looks very similar although the charge exchange reaction provides information on a broader energy range. Using the "merged analysis" one can obtain a full picture of the B(GT) over the full Q(beta) range. Looking at the individual transitions some differences are observed, especially for the weak transitions. Their possible origins are discussed.

We report the first observation of correlated x rays emitted by a heavy highly charged ion such as hydrogenlike uranium in the process of radiative recombination. The angular correlations between these x rays for the first time revealed a coherence of the populated state in this ion. The results also indicate a strong contribution of the spin-orbit interaction in radiative recombination.

The x-rays emitted in the process of radiative recombination (RR) of quasi-free electrons into 2p(3/2) excited state of hydrogenlike uranium ion were studied experimentally. Both the RR x-ray and the subsequently emitted Ly alpha(1) x-ray were detected in time-coincidences. The angular distribution of the Ly alpha(1) x-rays varied as a function of the RR x-ray emission direction. This observation revealed the coherent population of magnetic sublevels of the 2p(3/2) state in the hydrogenlike uranium ion.

We present a simple and versatile polarimeter for x rays in the energy range of 10-30 keV. It uses Compton scattering in low-Z materials such as beryllium or boron carbide. The azimuthal distribution of the scattered x rays is sampled by an array of 12 silicon PIN diodes operated at room temperature. We evaluated the polarimetry performance using Monte-Carlo simulations and show experimental results.

We consider the radiative recombination of a free electron into the excited 2p(3/2) state of heavy H-like ion with the subsequent decay into the ground 1s(1/2) state. Quantum correlations between two photons emitted in the process are studied.

We have studied the β decay of the Tz=−1,f7/2 shell nuclei Ni54,Fe50,Cr46, and Ti42 produced in fragmentation reactions. The proton separation energies in the daughter Tz=0 nuclei are relatively large (≈4–5 MeV) so studies of the γ rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision β-decay half-lives, excitation energies, and β branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these β decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths observed in beta decay including a sensitivity limit with the strengths of the Tz=+1 to Tz=0 transitions derived from high resolution (3He,t) reactions on the mirror target nuclei at RCNP, Osaka. The accumulated B(GT) strength obtained from both experiments looks very similar although the charge exchange reaction provides information on a broader energy range. Using the "merged analysis" one can obtain a full picture of the B(GT) over the full Qβ range. Looking at the individual transitions some differences are observed, especially for the weak transitions. Their possible origins are discussed.12 MoreReceived 24 June 2014Revised 18 October 2014DOI:https://doi.org/10.1103/PhysRevC.91.014301©2015 American Physical Society

We investigate the parity nonconservation effect in the elastic scattering of polarized electrons on heavy He-like ions, being initially in the ground state. The enhancement of the parity violation is achieved by tuning the energy of the incident electron in resonance with quasidegenerate doubly-excited states of the corresponding Li-like ion. We consider two possible scenarios. In the first one we assume that the polarization of the scattered electron is measured, while in the second one it is not detected. For the second scenario we propose a scheme of a modified electron beam ion source (EBIS) experiment where the detection of a parity violation in the electron scattering seems possible.

The linear polarization of x rays produced by dielectronic recombination into highly charged ions was for the first time measured at an electron beam ion trap using a newly developed Compton polarimeter. The experimental results open a possibility for diagnostics of anisotropies of hot plasmas. We also demonstrate a high sensitivity of the x-ray polarization to the Breit interaction.