Experimental Studies On Radiation Parameters Of Nb ?Levels

Natural radiation lifetime,branching ratio,transition probability and oscillator strength of atoms and ions radiation parameters has important significance in laser physics,analytic chemistry,atomic physics,plasma physics and astrophysics research.Atoms are absolutely identical in the universe,and can be measured accurately in the lab,so the atoms as an ideal remote detectors can help mankindunderstand deeply the vast space.In astrophysics,the precise abundance of the chemical elements in the stellar photospheres can provides indirect information for the researches of chemical component in stars,and the processes in stellar interiors.In the same time,the astrophysicists can infer the life of the stars or the universe and the evolution of stars or the universe by precise oscillator strength radiation parameters,so the atomic radiation parameter is one of the indispensable basic data for exploring outer space.In the laboratory,using the natural radiation lifetime with branching fractions to deduce oscillator strength is reliable and reliable,after,using the oscillator strength to determine the chemical element abundance.Combining the known oscillator strength and chemical element abundance data with the stellar spectrum data witch obtained by all kinds of large Ground and Space telescopes,we could understand some knowledge about the universe.Some radiation spectrum which are from some heavy-element stars contain a larger number of niobium spectrum,for example,the M-type long-period variable?LPV?o Ceti?Mira?and MS-type LPV,?Cyg.So measuring the Nb element spectra data has important research value for the study of stellar objects.Radiative lifetimes for Nb I are measured by time-resolved laser-induced fluorescence?TR-LIF?technique.In the process of experiment,a 532 nm Q-switched Nd:YAG laser was focused on a Nb target sample to produce Nb plasma where there were sufficient free atoms in metastable states and ground state,after appropriate delay time,The excitation laser was generated by a tunable dye laser which was pumped by another 532 nm Q-switched Nd:YAG laser sent through the plasma to excite the Nb atoms to the investigated levels,the fluorescence emitted from excited states are recorded by the fluorescent probe,the results of radiative lifetimes acquired by analyzing the fluorescence decay curves.Radiative lifetimes for 59 odd-parity levels of Nb I belonging to the 4d³5s5p and 4d⁴5p configurations except for one level with unknown configuration,which are in the energy range between 23910.9 and37188.28 cm^-1,the lifetime values range from 7.1 to 118.7ns with uncertainties less than 10%.And 52 lifetime values determined in this paper are reported for the first time.In the present work,we have tried to measure BFs for the levels whose lifetimes were measured by observing emission spectrum of a Nb hollow cathode lamp.Unfortunately,it was found that almost all the levels have emission lines overlapping with other lines belonging to atomic or ionic niobium in such a way that the BFs measurements could not be performed accurately.However,for 20 among the 59levels,it was possible to deduce some branching fractions from intensity measurements carried out using the Fourier transform spectra of niobium available at theKittPeakNationalSolarObservatory?NSO?digitallibrary?http://diglib.nso.edu/?.Combined radiative lifetimes with branches,we obtain transition probabilities and oscillator strengths for 129 spectrum line.