Open Access Dissertation
Date of Award
Physics and Astronomy
Models for stellar nucleosynthesis, age determinations for stars in the Milky Way's galactic halo, and stellar chemical abundance determinations are dependent upon accurate atomic spectroscopic data to allow the correct interpretation of stellar absorption and emission spectra. It is well known that calculations of many astrophysically important atomic parameters are limited due to line blending, insufficient spectral resolution of some key spectral lines, and also the complicated electronic structure of the important heavy elements. Astrophysicists have therefore looked to laboratory astrophysics experiments to provide accurate atomic data to help resolve these limiting issues. In this dissertation, laser-induced breakdown spectroscopy (LIBS) has been employed for the first time on a large scale as a spectroscopic technique for the rapid and convenient production of atomic and ionic plasmas as sources of atomic emission in order to determine radiative properties in astrophysically relevant lanthanides (Gd, Nd, Pr and Sm) and transition metals (Cu and Fe).
Nanosecond laser pulses incident on pure elemental targets in a rarified argon environment were used to create high-temperature plasmas. The resulting spontaneous emission from the high-temperature micro-plasmas was dispersed in a spectrally-corrected high-resolution broadband Échelle spectrometer, and detected with a high-sensitivity intensified CCD camera which allowed the simultaneous determination of the relative intensities of thousands of decay branches from hundreds of excited energy levels and multiple ionization states. These experimentally measured relative emission intensities were combined with previously obtained atomic lifetimes to calculate transition probabiliites and oscillator strengths.
In two transition metals, emission intensities have been measured for 192 transitions from 108 excited states in neutral copper and 27 emission lines from 108 excited states in singly-ionized copper as well as 776 emission lines from 108 excited states in neutral iron and 1453 emission lines from 108 excited states in singly-ionized iron.
In four important lanthanide elements, emission intensities have been measured for 587 lines of 113 excited states in neutral gadolinium, 480 lines from 43 excited states of singly-ionized gadolinium, and 40 lines in 6 states of doubly-ionized gadolinium; 121 emission lines from 93 excited states in neutral neodymium, 368 lines from 46 excited states in singly-ionized neodymium, and two lines from a single excited level of doubly-ionized neodymium; 19 lines from 19 excited levels of neutral praseodymium, 367 lines from 41 excited states in singly-ionized praseodymium, and 359 lines from 7 excited levels of doubly-ionized praseodymium; 137 lines from 70 excited states in neutral samarium, 713 lines from 115 excited states in singly-ionized samarium, and 49 lines from 17 excited levels of doubly-ionized samarium. The degree of uncertainty for strong emission lines is 9.3%, for moderate lines 10.3%, and 23.3% for weak transitions. This degree of uncertainty is typical for such laboratory astrophysics work and is usually an improvement upon available calculations.
Ryder, Caleb, "Oscillator strength measurements in singly-ionized, doubly-ionized and neutral lanthanides and transition elements (sm, nd, pr, gd, cu, and fe) using laser-induced breakdown spectroscopy." (2011). Wayne State University Dissertations. Paper 474.