Absolute measurements of photoionization cross-sections for ions (original) (raw)
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High-Resolution Measurements of Photoionization of Ions Using Synchrotron Radiation
AIP Conference Proceedings
Measurement of absolute cross sections for photoionization of ions has become feasible by merging a wellcollimated ion beam with a monochromatic beam of synchrotron radiation. An electron cyclotron resonance (ECR) ion source permits such measurements to be extended to multiply charged ions, and makes possible systematic studies along isoelectronic sequences. The evolution of atomic spectra along such sequences is commonly studied theoretically, but the predictive ability of the theoretical methods remains largely untested. Absolute cross-section measurements are presented for the first three ionic members of the isoelectronic sequence of nitrogen (O + , F 2+ and Ne 3+).
Photoionization of Astrophysically Relevant Atomic Ions at PIPE
We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple L-shell photoionization of Fe + , Fe 2+ , and Fe 3+ ions, and on single and multiple K-shell photoionization of C − , C + , C 4+ , Ne + , and Si 2+ ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact that the implementation of the photon-ion merged-beams method at one of the world's brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions. Atoms 2020, 8, 45 2 of 17 for U 91+ . Thus, photon energies from the vacuum ultraviolet (VUV) to the hard X-ray bands are needed for investigating photoionization of ions across the entire periodic table. Powerful laboratory sources for these types of radiation are hot plasmas and synchrotron light sources, which both have been used for photoabsorption and photoionization studies with atomic ions. The dual laser plasma (DLP) technique [12] uses a laser-generated hot plasma as a back-lighter for absorption measurements with ions in a second laser-generated plasma. In contrast to the broad spectral distribution of the radiation from a hot plasma, synchrotron radiation has a much narrower photon-energy bandwidth and it is freely tunable over large energy ranges. Moreover, modern third generation synchrotron light sources provide a high photon flux, which is a prime necessity for experiments with dilute targets, such as ions, whose mutual electrostatic repulsion entails low particle densities. The density of ionic targets can be increased in ion traps, where the ion cloud can be compressed by external fields and its density can be increased by applying cooling techniques. Nevertheless, the signal rates from such arrangements are usually still rather low and, therefore, photoionization of trapped atomic ions has been performed in only a few cases , so far.
Photoionization of Multiply Charged Ions at the Advanced Light Source
AIP Conference Proceedings, 2005
Photoionization of multiply charged ions is studied using the merged-beams technique at the Advanced Light Source. An ion beam is created using a compact 10-GHz all-permanent-magnet ECR ion source and is accelerated with a small accelerator. The ion beam is merged with a photon beam from an undulator to allow interaction over an extended path. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences. FIGURE 1. Schematic diagram of ion-photon mergedbeams end station.
The Absolute Cross Section forL‐Shell Photoionization of C+Ions from Threshold to 105 eV
The Astrophysical Journal Supplement Series, 2001
The absolute cross section for photoionization of C`ions has been measured from the ionization threshold at 24 eV to 105 eV by overlapping an ion beam with a monochromatized synchrotronradiation beam from the ASTRID undulator. The measurements, which are important for astrophysical modeling of, for example, stellar atmospheres, have been compared with R-matrix calculations from the Opacity Project and the Iron Project. The general agreement between theory and experiment is good, yet di †erences in the magnitude of the cross section of up to 50% are observed as well as some deviations concerning the resonance structure. Subject headings : atomic data È atomic processes
Absolute photoionization cross section measurements of O II ions from 29.7 to 46.2 eV
2008
ABSTRACT Absolute photoionization cross sections have been measured for a mixture of ground-state and metastable O II (O+) ions at photon energies ranging from 29.9 to 46.0 eV (414.7 to 269.5 Å). All measurements were performed by merging an O+ beam with synchrotron radiation from an undulator beam line at the Advanced Light Source (ALS). At a resolution of 17 meV, more than 70 spectral features have been resolved, most of them identified and characterized.
Absolute cross sections for photoionization of Xeq +ions (1 ⩽ q ⩽ 5) at the 3d ionization threshold
Journal of Physics B, 2014
The photon-ion merged-beams technique has been employed at the new Photon-Ion spectrometer at PETRA III (PIPE) for measuring multiple photoionization of Xe q+ (q=1-5) ions. Total ionization cross sections have been obtained on an absolute scale for the dominant ionization reactions of the type hν + Xe q+ → Xe r+ + (q − r)e − with product charge states q + 2 ≤ r ≤ q + 5. Prominent ionization features are observed in the photon-energy range 650-750 eV, which are associated with excitation or ionization of an inner-shell 3d electron. Single-configuration Dirac-Fock calculations agree quantitatively with the experimental cross sections for non-resonant photoabsorption, but fail to reproduce all details of the measured ionization resonance structures.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2011
A crossed photon-atom beam apparatus has been constructed for absolute measurement of total photoionization cross sections of isolated and neutral metallic atoms. The main purpose is to establish the technique which can be used as widely as possible for the metallic elements. Using this apparatus, measurements on Ba and Eu atoms have been made at selected energies in their 4d giant resonance regions 110-140 eV and 140-180 eV, respectively. A monochromatized synchrotron radiation was used as a light source. The target-atom density in the interaction section was determined with accuracy of 9% using the accumulation rate of metallic atoms on a quartz crystal sensor and the average velocity of the atoms obtained by a time-of-flight method combined with a pulsed electron gun. The number of photons was determined with use of a double-ion chamber preferably. The entire systematic errors have been estimated to be 20% for Ba and 27% for Eu. The comparison of the measured cross-section values with previous experimental and theoretical results is reasonable, indicating that the crossed photon-atom beam method is fairly promising technique.
Physical Review Letters, 1991
The first measurement of photoelectron spectra emitted in the photoionization of a singly charged-ion beam by synchrotron radiation is reported. A Ca-ion beam is resonantly photoionized by the monochromatized photon beam of the SU6 undulator of the SuperACO Storage Ring at 33.20 eV photon energy. The values observed for the kinetic energy and for the intensity of the photoelectron line are in good agreement with the predicted values. The success of this feasibility experiment opens up wide opportunities for similar photoionization and Auger studies on multiply charged ions.
A method for measuring light ion reaction cross-sections
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
An experimental procedure for measuring reaction cross-sections of light ions in the energy range 20-50 MeV/ nucleon, using a modified attenuation technique, is described. The detection method incorporates a forward detector that simultaneously measures the reaction cross-sections for five different sizes of the solid angle in steps from 99.1% to 99.8% of the total solid angle. The final reaction cross-section values are obtained by extrapolation to the full solid angle.
Physical Review A, 2003
Cross sections for the photoionization ͑PI͒ of Sc 2ϩ ions with ͓Ar͔3d ground-state configuration have been measured by employing the merged ion-photon beams method. The Sc 2ϩ ions were produced from metallic vapor in an electron cyclotron resonance ion source, and the photon beam was generated by an undulator in the electron-synchrotron storage ring of the advanced light source of the Lawrence Berkeley National Laboratory. The experimental photon energy range 23-68 eV encompasses the direct 3d and 3p photoionization thresholds. The experimental photoion spectrum is dominated by autoionizing resonances due to 3p excitations predominantly decaying via Coster-Kronig and super-Coster-Kronig transitions. Individual resonances located around EϷ40.2 eV have been measured with an instrumental energy spread ⌬E as low as 1.2 meV, corresponding to a resolving power of E/(⌬E) around 33 500. The fractions of metastable ions in the Sc 2ϩ ion beam are obtained by comparing the photoionization cross section with the recently measured ͓Schippers et al., Phys. Rev. A 65, 042723 ͑2002͔͒ cross section for the time-reversed process of photorecombination of Sc 3ϩ ions. Absolute strengths of several 3p 5 3d 2 and 3p 5 3d 4s PI resonances have been determined. They are the same as the corresponding resonance strengths for isoelectronic Ca ϩ ions.