Investigations On Radiative Parameters Of Iron-peak Elements: MnⅠ, NiⅠ And Rare-earth Elements: YⅠ, LaⅠ And La Ⅱ

With the development of observational techniques, people obtain high resolutionand high signal-to-noise ratio astronomical spectrum. The high quality spectrumbrings new opportunity and challenge to the study of the material structure, physicalstate and physical progress of various types of astronomical bodies. The elementabundance and its evolution have close association with many important subjects inastrophysics. Oscillator strengths of atomic or ionic species are required in analyses ofastrophysical spectra for elemental abundance estimation. Long-time experiments ofthe astronomers in abundance analysis and synthetic spectrum calculations lead to theconclusion that oscillator strengths from laboratory measurements have a priority inall kinds of spectral analyses. It is well known that the combination of radiativelifetime and branching fraction is one of the most accurate and reliable method ofobtaining oscillator strengths. Moreover, radiative lifetimes, branching fractions andoscillator strengths (transition probabilities) are also important in testing the quality ofwave function and improving the atomic structure theoretical model.Iron-peak elements are represented in photospheric spectrum by numerous linesof the neutral and once ionized species. For such elements, because of their rather lowionization potentials, the dominant species is the ionized one (95%) while the neutralspecies are less (5%). When changed the physical conditions, such as the temperature,the minor species may changed by a factor of2(5%to10%). This means that theneutral species are very sensitive to physical conditions of the photosphere and goodfor testing a model atmosphere. Therefore, the investigation of the radiative parameterof iron-peak elements is important for astrophysics. Recently, the rare-earth elementswere frequently observed in astrophysical spectra. In particular, the abundance of therare-earth elements in chemically peculiar stars is a factor of103to105whencompared to the solar system value. The rare-earth element abundances are helpful inimproving stellar nucleosynthesis theories. So the rare-earth elements have caused great attention in astrophysical research. In view of the needs in astrophysicalinvestigation for the iron-peak and rare-earth element parameters, this paper focus onthe radiative parameter measurements of MnⅠ, NiⅠ,MnⅠ, NiⅠ, and LaⅡ and obtainlots of reliable results.In this paper, free atoms or ions is obtained by laser-induced plasma technique.Using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy, free atoms orions populated in lower energy levels can be selectively excited to the aim energylevel and the fluorescence decay signal emitted from the excited state is recorded forlifetime estimation. The lifetime value were obtained by fitting the recordedfluorescence curve to an exponential function with adjustable parameters or by fittingthe fluorescence signal to the convolution of the detected laser pulse and a exponentialfunction. In the branching fraction measurements, a hollow-cathode lamp with argoncarrier gas is used as the emission source. Since the detection system has differentintensity response for different wavelengths, the recorded line intensity needs to becorrected by the response value. Branching fractions can be calculated by all the lineintensities emitted from the same upper level. Transition probabilities and oscillatorstrengths can be determined by combining lifetimes and branching fractions.Using experimental methods as above statements, this thesis completes the workas below:1) Radiative lifetimes for32excited levels of MnⅠ and for17excited levelsof NiⅠ were measured. The energy regions are from45754.27to54950.81cm1forMnⅠ and from28578.018to50851.199cm1for NiⅠ. To our best knowledge,26lifetime results of MnⅠ and9lifetime results of NiⅠ are reported for the first time.2)Radiative lifetimes of40excited levels of La I, in the energy range from24507.87to52030.4cm1, and20levels of LaⅡ, in the range from26414.01to56035.70cm1,were measured in this work. To our best knowledge,34lifetimes of La I and17lifetimes of LaⅡ are reported for the first time. In addition, the J values of the levels51939.2and52030.4cm1given by Martin et al.(1978) were1/2or3/2, but in thepresent work it is found that they should be taken as3/2based on the angularmomentum selection rule of electric dipole transition.3) Radiative lifetimemeasurements are reported for34levels of Y I between27824.50and50254.0cm1among which27lifetimes are reported for the first time. Besides, parameter measurements based on the emission spectrum of a hollow cathode lamp wereperformed for12of these levels and the results of64lines between274.250and670.063nm were obtained. By combining them with lifetime values, the transitionprobabilities and absolute oscillator strengths of these lines were determined. Theuncertainties are within10%for all the lifetimes and for most branching fractions,transition probabilities and oscillator strengths.In a word, radiative liftetimes, branching fractions, transition probabilities andoscillator strength measured in this work are key atomic data for astrophysicsinvestigation. Accurate atomic data are used in improving stellar atmosphere model,determining element abundances and testing stellar nucleosynthesis theories.Furthermore, these data can also be applied in the fields such as laser physics, plasmadiagnosis and nuclear fusion.