Browsing by Author "Berger, Lukas"
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Item Natural-linewidth measurements of the 3𝐶 and 3𝐷 soft-x-ray transitions in Ni xix(Physical Review A, 2024-06-10) Shah, Chintan; Kühn, Steffen; Bernitt, Sonja; Steinbrügge, René; Togawa, Moto; Berger, Lukas; Buck, Jens; Hoesch, Moritz; Seltmann, Jörn; Kozlov, Mikhail G.; Porsev, Sergey G.; Gu, Ming Feng; Porter, F. Scott; Pfeifer, Thomas; Leutenegger, Maurice A.; Cheung, Charles; Safronova, Marianna S.; Crespo López-Urrutia, José R.We used the monochromatic soft-x-ray beamline P04 at the synchrotron-radiation facility PETRA III to resonantly excite the strongest 2𝑝−3𝑑 transitions in neonlike Nixix ions, [2𝑝6]𝐽=0→[(2𝑝5)1/23𝑑3/2]𝐽=1 and [2𝑝6]𝐽=0→[(2𝑝5)3/23𝑑5/2]𝐽=1, respectively dubbed 3𝐶 and 3𝐷, achieving a resolving power of 15 000 and signal-to-background ratio of 30. We obtain their natural linewidths, with an accuracy of better than 10%, as well as the oscillator-strength ratio 𝑓(3𝐶)/𝑓(3𝐷)=2.51(11) from analysis of the resonant fluorescence spectra. These results agree with those of previous experiments, earlier predictions, and our own advanced calculations.Item New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem(Physical Review Letters, 2022-12-05) Kühn, Steffen; Cheung, Charles; Oreshkina, Natalia S.; Steinbrügge, René; Togawa, Moto; Bernitt, Sonja; Berger, Lukas; Buck, Jens; Hoesch, Moritz; Seltmann, Jörn; Trinter, Florian; Keitel, Christoph H.; Kozlov, Mikhail G.; Porsev, Sergey G.; Gu, Ming Feng; Porter, F. Scott; Pfeifer, Thomas; Leutenegger, Maurice A.; Harman, Zoltán; Safronova, Marianna S.; López-Urrutia, José R. Crespo; Shah, ChintanOne of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio Rexp=f3C/f3D=3.51(2)stat(7)sys agrees with our state-of-the-art calculation of Rth=3.55(2), as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.