Oscillator strength measurements in samarium(II), neodymium(II) and praseodymium(II)

A knowledge of the abundances of lanthanide ions in stellar photospheres is valuable in astrophysics, especially for chemically peculiar stars. However, the determination of elemental abundances is often limited by inadequate knowledge of oscillator strengths.;In the previous work of our group, the lifetimes of Sm II, Nd II and Pr II were obtained. In this thesis work, we measured the corresponding branching fractions of these lanthanide ions using a fast-ion-beam laser-induced-fluorescence technique. The power of this technique is that ions are selectively excited by a laser, which ensures that every branch comes from a single upper level and gets rid of spectral blends. Besides, the low ion-beam density ensures that the systematic errors due to collisions and radiation trapping are negligible.;Combining the branching fractions with our previously measured lifetimes, we obtained 608, 430 and 260 oscillator strength values for Sm II, Nd II and Pr II transitions, respectively, over the wavelength range 350-850 nm. These transitions originate from 69 upper levels in the range 21 655 cm-1 -29 388 cm-1 for Sm II, 46 upper levels in the range 22 697 cm-1-29 955 cm-1 for Nd II, and 32 levels in the range 22 040 cm-1-28 577 cm-1 for Pr II. Of the 260 measured oscillator strength values of Pr II, 183 have been determined accurately for the first time. The uncertainties arise principally from systematic uncertainties of the efficiency calibration of the optical detection system (7.1%), with smaller statistical contributions (1.5%). Comparisons are made to prior measurements.;Keywords. lanthanide ions, branching fractions, oscillator strength, lifetime, fast-ion-beam, laser-induced-fluorescence;Combining independently measured values of radiative lifetimes and branching fractions is an effective and precise method to measure oscillator strengths. It avoids absolute intensity measurements, requiring a knowledge of the absolute number density of particles and absolute measurements of intensity, and furthermore decreases the systematic error greatly.