【作者】 张巍；

【导师】 戴振文；

【作者基本信息】 吉林大学 ， 光学， 2011， 博士

【摘要】 在天体物理中,天体化学元素丰度的分析是研究星系化学演化、验证元素核合成理论和确定行星系统形成条件的重要途径。结合天文望远镜观测到的天体光谱中元素谱线的宽度、相对强度及振子强度能确定该元素在该星体中的元素丰度。目前,将辐射寿命与分支比数据相结合是实验确定振子强度的最准确方法之一,所以在天体物理研究领域,原子离子的能级自然辐射寿命的测量研究具有重要意义。第五、六周期元素是化学特殊星(CP星)、炽热恒星等天体中元素丰度较大的一类元素。鉴于此,我们对其中的锡、钡、钐和铕四种元素原子和离子的能级辐射寿命进行了系统的测量研究。本论文采用的实验方法是时间分辨激光诱导荧光光谱技术,激发方案采用的是一步激发方案。利用一步激发方案和激光诱导等离子体产生原子和离子的方法,对锡原子38个位于43682.737到56838.68 cm-1之间的属于5pnd(n=5-8),5pns(n=7,9和10)和5s5p3组态的奇宇称能级的自然辐射寿命进行了测量,其中28个能级的结果是文献中未见报道的。此外,测量了钡原子的70个位于30815.512到41759.93 cm-1之间的奇宇称能级的自然辐射寿命,其中66个能级的寿命结果是文献中未见报道的；还测量了钐原子的143个位于18985.70到34723.16 cm-1之间的奇宇称能级的自然辐射寿命,其中137个寿命结果是文献中未见报道的；另外还测量了53个一价钐离子奇宇称能级的自然辐射寿命,其中31个寿命结果是文献中未见报道的。在所研究的钐离子能级中,7个能级位于35000 cm-1以上,而此能级范围内钐离子能级寿命的测量工作很少。最后,我们还测量了铕原子偶宇称高激发态186个能级和奇宇称高激发态9个能级的自然辐射寿命,其中180个寿命结果是文献中未见报道的；同时也测量了铕离子偶宇称高激发态11个能级的寿命,其中8个寿命结果是文献中未见报道的。总之,本论文较系统地测量了天体光谱分析所需的一些重要元素原子和离子自然辐射寿命。这些测量研究结果不仅为原子结构理论的发展和天体光谱分析提供了一批新的原子数据,而且对等离子体物理、激光物理和热核反应等方面的研究和应用也具有重要的参考价值。更多还原

【Abstract】 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 SmⅠhave 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 SmⅡ, 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 EuⅠhave been measured, among them, 180 lifetimes were measured for the first time. And the radiative lifetimes of 11 even-parity levels in EuⅡhave 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.更多还原