Abstract
This work reports on the application of a novel electric field-ionization setup for high-resolution laser spectroscopy measurements on bunched fast atomic beams in a collinear geometry. In combination with multi-step resonant excitation to Rydberg states using pulsed lasers, the field ionization technique demonstrates increased sensitivity for isotope separation and measurement of atomic parameters over previous non-resonant laser ionization methods. The setup was tested at the Collinear Resonance Ionization Spectroscopy experiment at ISOLDE-CERN to perform high-resolution measurements of transitions in the indium atom from the text {5s}^2text {5d},^2text {D}_{5/2} and text {5s}^2text {5d},^2text {D}_{3/2} states to text {5s}^2np ^2P and text {5s}^2ntext {f},^2F Rydberg states, up to a principal quantum number of n=72. The extracted Rydberg level energies were used to re-evaluate the ionization potential of the indium atom to be 46,670.107(4),hbox {cm}^{-1}. The nuclear magnetic dipole and nuclear electric quadrupole hyperfine structure constants and level isotope shifts of the text {5s}^2text {5d},^2text {D}_{5/2} and text {5s}^2text {5d},^2text {D}_{3/2} states were determined for ^{113,115}In. The results are compared to calculations using relativistic coupled-cluster theory. A good agreement is found with the ionization potential and isotope shifts, while disagreement of hyperfine structure constants indicates an increased importance of electron correlations in these excited atomic states. With the aim of further increasing the detection sensitivity for measurements on exotic isotopes, a systematic study of the field-ionization arrangement implemented in the work was performed at the same time and an improved design was simulated and is presented. The improved design offers increased background suppression independent of the distance from field ionization to ion detection.
Highlights
Rydberg level energies were used to re-evaluate the ionization potential of the indium atom to be
The ability to separate and study small quantities of isotopes from a large ensemble without losses is the limiting factor of many experimental studies in modern nuclear physics[1,2,3,4], as exotic isotopes of interest can often only be produced at low rates and their accumulation into substantial quantities is prevented by their short half-lives
The acceleration creates a kinematic separation in the transition frequency of the naturally abundant isotopes 115 In (95.72%) and 113 In (4.28%), which greatly enhances the isotope selectivity compared to in-source laser spectroscopy separation or measurement techniques[5,46], laser induced breakdown spectroscopy (LIBS)[47] or in-gas cell laser ionization spectroscopy (IGLIS)[48]
Summary
Rydberg level energies were used to re-evaluate the ionization potential of the indium atom to be. Fast beam collinear laser spectroscopy techniques have allowed high-precision measurements on short-lived isotopes, down to rates of fewer than 100 ions per s econd[3,12,13] These approaches use the Doppler compression of an accelerated atomic beam to enable high-precision laser spectroscopy measurements to be performed in a collinear geometry[14,15]. This technique is being implemented at radioactive ion beam facilities worldwide, giving a resolution of a few 10s of MHz, which is sufficient to resolve the hyperfine structure for nuclear physics studies[16,17,18,19]. Motivated by a need for higher sensitivity to access exotic isotopes produced at rates lower than a few ions per second, a variation of the technique, the Collinear Resonance Ionization Spectroscopy (CRIS)[20,21] experiment at Scientific Reports | (2020) 10:12306
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