Measurments Of The Natural Radiative Lifetimes Of Levels Of Some Important Atoms And Ions In Astronomical Spectroscopy

Currently, the primary method that human obtained the knowledge about the universe and celestial body is spectral analysis. Using the radiatvie parameters of atom and molecular to analyze the spectral data obtained by Astronomical observation, and then to determinate the state of the universe and the evolution of celestial bodies was the basic approach.Because fifth and sixth period elements were such element group that the element abundances in the special stars (CP stars), hot stars and other celestial bodies were larger, the investigative interesting of their radiative parameters was inspired. In addition, for the complicated atomic structure of these elements, the theoretic calculation of their accurate spectrum was inconvenient, and the highly approximative theoretic model has to be used for investigation. Therefore the larger accurate experimental data were needed to verify the theoretic model. So, the experimental investigation about the radiative parameters of these elements was very important for the atomic theory and the analysis of spherical spectrum.Recently, with the developing of laser spectroscopy, the radiative characteristic of these elements can be investigated accurately. In this paper, using the scheme of one step exciting, we measured the radiative lifetimes of some elements, which were interesting for the analysis of spherical spectrum. That supplied the credible atomic and ionic radiative parameters for astrophysics.In the experiment using time-resolved laser-induced fluorescence (LIF) technique, the scheme of one step exciting and the laser produced plasma technique, the experimental lifetimes of 38 highly-lying odd-parity levels in the 5pnd (n=5-8),5pns (n=7,9 and 10) and 5s5p3 configurations of Sn I in the range from 43682.737 to 56838.68 cm-1 were measured, and 28 lifetimes were reported for the first time. The radiative lifetimes of 70 high-lying odd-parity levels of Ba I in the range from 30815.512 to 41759.93 cm-1 also were measured, among them,66 lifetimes were measured for the first time. In addition, the lifetimes of 79 odd-parity levels belonging to J=0,1,2,3 series and 64 odd-parity levels belonging to J=4,5,6, and 7 series in Smâ… have been measured, among them,137 lifetimes were measured for the first time. And we also have measured the radiative lifetimes of 53 odd-parity levels of Smâ…¡, in which 31 results were reported for the first time. In our radiative lifetime investigation, seven upper levels above 35000 cm-1, in such level region the knowledge is inadequate, have been included. Finally, the experimental lifetimes of 186 high-lying even-parity levels and nine odd-parity highly excited levels of Euâ… have been measured, among them, 180 lifetimes were measured for the first time. And the radiative lifetimes of 11 even-parity levels in Euâ…¡have been determined for the fist time. In the experiment, in order to spread the ranges of laser wavelengths, we not only employed the double and triple frequency techniques in nonlinear crystal, but also used the excited Laman shift method. In addition, in the technique of ablation, a digital delay generator (SRS Model 535) was used to contral the delay times between the excitation pulse and ablation pulse, and then to adjust the physical states of atom and ion.In the measurements, due to the complexity of the atomic structure and spectrum, for insuring the correctness of the excitation, all transition channels of each element have been calculated, and the channel with a lager interval between adjacent channels was selected for exciting channel. For futher verifying the correctness, observing the consistent of the decay lifetimes with selecting several exciting channels to populate the investigated level was employed. During detecting, for good Signal-to-Noise, the flouresence channel with lager intension was selected for detective channel. And the detective system was maked up of monochromator, photomultiplier tube (risetime=2 ns) and 500 MHz digital oscilloscope. In addition, various effects have been checked and eliminated by different effective methods.In the evaluation of lifetime, for a level with a long lifetime, the lifetime value may be evaluated by a least-square exponential fitting to the recorded fluorescence curves. For the levels with shorter lifetimes, a deconvolution of the fluorescence decay curves is necessary to obtain the true lifetime of the levels to eliminate the effect of the width of exciting pulse and the instrumental response function. Finally, for each level, about 15 curves were recorded under different experimental conditions, and the lifetimes evaluated from them were averaged to obtain the final lifetime results.In a word, using the technique of time-resolved laser spectroscopy, the radiative characteristics of the atomic and ionic level of some elements interesting in the analysis of spherical spectrum have been investigated. It not only supplied the new atomic data for astrophysics, but also was very important for plasma physics, laser physics and hot nuclear reaction.