Resonant coherent excitation of the lithiumlike uranium ion: A scheme for heavy-ion spectroscopy

We report our observation of the resonant fluorescence from highly charged uranium ions. Using the resonant coherent excitation (RCE) technique, the $2s$-$2p_{3/2}$ transition in 191.68 MeV/u Li-like U${}^{89+}$ ions was excited at 4.5 keV with a resonance width of 4.4 eV. The result demonstrated that the RCE can be applied to resonant fluorescence spectroscopy of high-$Z$ ions up to uranium with high efficiency and resolution.

Figure 1

Relationship between beam energy and atomic number required to observe the RCE process. The lines are calculated for the $1s$-$2p$ transition in H-like ions, and the $2s$-$2p_{1/2}$ and $2s$-$2p_{3/2}$ transitions in Li-like ions. The dots show experimental data reported to date.

Figure 2

(a) Schematic layout of the experimental setup. (b) The charge state distribution of the beam exiting the target crystal under random and (220) channeling conditions. The inset shows the (220) channeling trajectory simulation for the 193 MeV/u U${}^{89+}$ ions in a 10-$\mu$m-thick Si crystal.

Figure 3

(a) X-ray energy spectra observed with SDD No. 3 for different $\theta$. (b) The total number of x rays observed with SDDs No. 2, No. 3, and No. 4 as a function of $\theta$. The solid line is a Gaussian curve fitted to the data.