共查询到20条相似文献,搜索用时 125 毫秒
1.
将门控分幅相机与平面晶体谱仪耦合,构成时间分辨光谱测量系统,对Al激光等离子体的K壳层发射谱进行测量,获得了相对入射激光延迟约1ns,积累时间约200ps的光谱信号。利用稳态碰撞-辐射平衡(CRE)近似条件下的等离子体光谱辐射动力学模型,给出了Al激光等离子体Ly-β线与He-β线强度比以及Ly-γ线与He-γ线强度比与电子温度的函数关系。在此基础上,根据实验谱线强度比,得到激光强度为2.319×1014,1.937×1014和3.946×1014 W/cm2时,等离子体冕区电子温度分别为1.190(1±27%),1.165(1±27%)和1.525(1±27%)keV。 相似文献
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采用提拉法成功生长尺寸为φ30 mm× 75 mm的15at.%Yb3+:Gd2SiO5单晶, 并用Reitveld全谱拟合方法确定了其晶格常数、原子坐标和温度因子等参数. 用吸收光谱计算了Yb3+离子2F7/2↔ 2F5/2能级跃迁的振子强度、谱线强度、跃迁概率、 能级寿命和积分发射截面等光谱参数, 并根据激光性能评估得出结论: 表明该晶体具有较大的阈值特性, 有望采用大功率激光二极管泵浦实现可调谐或超快激光输出. 相似文献
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报道了在20 TW皮秒激光器上完成的p偏振激光与等离子体相互作用过程中产生的快电子的角分布和能谱测量结果。实验得到:当激光功率密度小于1017 W/cm2时,电子发射没有明显定向性,在激光入射面内多峰发射;当激光功率密度大于1017 W/cm2,小于1018 W/cm2时,电子主要沿靶面法线方向发射;当激光功率密度达到相对论强度时,电子主要沿激光传播方向发射;激光功率密度未达到相对论强度时,靶后表面法线方向快电子能谱拟合平均温度符合共振吸收温度定标率;激光功率密度达相对论强度以上时,靶后表面法线方向快电子能谱拟合平均温度高于已有的温度定标率。 相似文献
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本文应用坩埚下降法技术在全密封铂金坩埚条件下生长了不同Pr3+离子掺杂浓度的高质量LiLuF4单晶. 测定了单晶体从420 nm至500 nm的激发光谱. 在446 nm光激发下,观察到单晶体480 nm(3P0→3H4)蓝色发射带、522 nm(3P1→3H5)绿色发射及605 nm(1D2→3H4)的红色发射,其对应的平均寿命分别为38.5、37.3和36.8 μs. 其荧光寿命明显大于Pr3+掺杂的氧化物单晶. 同时研究了激发波长和掺杂浓度对发射强度以及色度坐标的影响. 获得最佳的Pr3+浓度为∽0.5 mol%,并分析了环境温度从298 K 到443 K变化对荧光强度的影响. 结果表明随着温度的增加,荧光强度逐步变弱,其中3P0→3H4(480 nm)能级跃迁受温度影响最大,其次是3P1→3H5和1D2→3H4. 相似文献
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在25MeV/u 40Ar+natAg、209Bi反应中,用4个PPAC和11组望远镜完成了关联裂变碎片与发射轻粒子的符合测量,角关联描绘为两个被探测到碎片折叠角θff的函数,线性动量转移〈LMT〉由测量到的角关联推出.将符合测量得到的对应于不同窗的后角轻带电粒子能谱用Maxwell分布来拟合其谱的后沿,经过一些修正,由能谱得到热核的初始温度Tint,在考虑反应Q值和预平衡发射的修正之后,可以得到不同窗所对应的激发能.实验结果表明,在40Ar+natAg、209Bi反应的中心碰撞中激发能分别为4.2、2.4MeV/u,而温度达6.1、5.5MeV,在半中心碰撞中激发能为3.5、1.9MeV/u,温度可达5.8、4.8MeV. 相似文献
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利用BUU模型模拟核-核碰撞36Ar+108Ag(35Mev/u)、14N+108Ag(35MeV/u)中的平衡前中子发射.模拟结果与唯象的运动源拟合给出的中等速度源成份相吻合.这说明中等速度源成份产生于核-核碰撞的早期,对应平衡前发射.并从级联碰撞的角度定量地研究了平衡前发射的持续时间. 相似文献
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将超导离子源提供的10—20keV/q Ar16+和Ar17+离子入射到Zr金属表面,在相互作用中产生的X射线谱表明,高电荷态Ar16+离子在金属表面中性化过程中有可能存在多电子激发,使Ar16+的K壳层电子被激发形成空穴,在退激过程中发射特征Kα-X射线.空心原子Ar的K层发射X射线强度随入射离子的动能而减弱,靶原子Zr的L壳层发射X射线强度随入射离子动能的增加而增强.Ar17+的单离子的Kα- 相似文献
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在C=C伸缩振动频率为1630厘米-1的区域内,观察到了未取代的丙烯酸及其酯系列化合物的C=C吸收谱带分裂为二,当α或β碳原子上的氢被甲基取代后,C=C吸收谱带不再分裂。根据C=C分裂谱带强度的温度效应及溶剂效应以及所得光谱的初步分析,认为C=C谱带的分裂是由于费米共振的结果,而不是由于顺、反两种构象平衡或其他原因,按照谱带的简单分析,C=C谱带的分裂可能是由于=CH的面外变角振动967厘米-1与C—C=C骨架振动662厘米-1的组频与C=C伸缩振动1630厘米-1产生费米共振的结果。 相似文献
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XIAO Hua-Lin LI Xiao-Bo ZHENG Dong CAO Jun WEN Liang-Jian WANG Nai-Yan 《中国物理C(英文版)》2010,34(11):1724-1728
Liquid scintillators are widely used as the neutrino target in neutrino experiments.The absorption and emission of different components of a ternary liquid scintillator(Linear Alkyl Benzene(LAB)as the solvent,2,5-diphenyloxazole(PPO)as the fluor and p-bis-(o-methylstyryl)-benzene(bis-MSB)as wavelength shifter)are studied.It is shown that the absorption of this liquid scintillator is dominant by LAB and PPO at wavelengths less than 349 nm,and the absorption by bis-MSB becomes prevalent at the wavelength larger than 349 nm.The fluorescence quantum yields,which are the key parameters to model the absorption and re-emission processes in large liquid scintillation detectors,are measured. 相似文献
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G. Brauer W. Anwand W. Skorupa C. Teichert J. Cizek P.G. Coleman A. Kohyama 《Applied Surface Science》2006,252(9):3342-3351
A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy and various positron spectroscopies (slow positron implantation, positron lifetime and re-emission). It is found that besides its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented. 相似文献
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Peter W. Peratt A.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(1):49-55
The radiation spectrum for synchrotron-emitting electrons in galactic-sized Birkeland current filaments is analyzed. It is shown that the number of filaments required to thermalize the emission spectrum to blackbody is not reduced when a non-Maxwellian electron distribution is assumed. If the cosmic background radiation (CBR) spectrum (T =2.76 K) is due to absorption and re-emission of radiation from galactic-sized current filaments, higher-order synchrotron modes are not as highly self absorbed as lower-order modes, resulting in a distortion of the blackbody curve at higher frequencies. This is especially true for a non-Maxwellian distribution of electrons for which the emission coefficient at high frequencies is shown to be significantly less than that for a Maxwellian distribution. The deviation of the CBR spectrum in the high-frequency regime may thus be derivable from actual astrophysical parameters, such as filamentary magnetic fields and electron energies in the model 相似文献
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Simultaneous measurements have been made of blister formation and gas re-emission during bombardment of Ni with 8–40 keV 3He+ at room temperature. It is shown that re-emission and blister formation start at the same critical fluence. An initial peak in the re-emission rate is correlated to a step in the total number of blisters. A more detailed analysis of the experimental data shows that the area contributing to gas re-emission is much larger than the blister area. This suggests the formation of an interconnected layer below the surface in which cracks at blister sites provide gas emission channels to the surface. 相似文献
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A terahertz time domain spectroscopy experiment is used to study the coherent re-emission after exciting more than 60 energy rotational states of OCS molecules in gas phase. Due to the regular structure of the absorption spectrum of such linear molecules, a set of subsequent pulses separated by 82.6 ps is re-radiated from the vapour and recorded up to 450 ps. A model based on a linear response of the gas and by use of “Maxwell-Bloch” equations has permitted the re-emitted free induced decay to be investigated. Spectroscopic parameters, such as rotational constant, centrifugal distortion coefficient and relaxation times are responsible for the temporal shape and so can be evaluated. The influence of the optical thickness to access the relaxation times is discussed. 相似文献
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采用开放光程可调谐二极管激光吸收光谱技术和反向拉格朗日随机扩散模型,通过田间试验,开展基于高时间分辨率数据的农田氨挥发研究,旨在为揭示农田氨挥发的动态变化规律提供新技术新方法。结果表明,TDLAS-bLS法能有效监测农田氨挥发动态,尤其是日内变化规律。豫北平原潮土农田夏玉米追肥后日内氨挥发有两个挥发峰值,分别在9:00和14:00左右,第一个高峰是由于夜晚溶解在露水中的氨气随露水蒸发而再次挥发,第二个高峰受地温和光照影响所致。追肥后氨挥发速率迅速升高,但挥发高峰期持续时间较短,集中于前四天,整个监测期内氨挥发损失约25.3%。TDLAS-bLS法与通气法相比,测定结果有一定差异。 相似文献
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Excitation and Emission of an Atom in Its Interaction with an Ultrashort Electromagnetic Field Pulse
Based on the approximation of sudden perturbations, the excitation and ionization of an atom in its interaction with an ultrashort electromagnetic field pulse are examined. The probabilities of excitation and ionization are obtained together with the spectra and cross sections of pulse re-emission by the atom. 相似文献
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Development of the spectrum of gamma-ray burst pulses influenced by the intrinsic spectral evolution and the curvature effect 下载免费PDF全文
The spectral evolution of gamma-ray burst pulses assumed to arise from
the emission of fireballs is explored. It is found that due to the
curvature effect, the integrated flux is well related to peak energy
by a power law in the decaying phase of pulses, where the index is
about 3, which does not depend on intrinsic emission and the Lorentz
factor. The spectra of pulses in the decaying phase are slightly
different from each other when different intrinsic spectral
evolution patterns are considered, indicating that it is dominated
by the curvature effect. In the rising phase, the integrated flux
keeps increasing whilst the peak energy remains unchanged when the
intrinsic emission bears an unchanged spectrum. Within this phase,
the flux decreases with the increase of the peak energy for a
hard-to-soft intrinsic spectrum, and for a soft-to-hard-to-soft
intrinsic spectrum, the flux generally increases with the increase
of the peak energy. An intrinsic soft-to-hard-to-soft spectral
evolution within a co-moving pulse would give rise to a pulse-like
evolutionary curve for the peak energy. 相似文献
19.
Karl F. Canter 《Hyperfine Interactions》1992,73(1-2):159-171
The present status of low energy positron diffraction (LEPD) and positron reemission microscopy (PRM) is reviewed in the context
of unanswered questions regarding the elastic scattering of positrons in the 1–300 eV energy range from atoms in solids and
at solid surfaces. Recent LEPD studies yield an agreement between theoretical and experimental diffraction intensities for
semiconductors that has never been equalled in electron diffraction studies. This situation is discussed in terms of the repulsive
interaction between the positron and the embedded atomic potential and the lack of exchange with the nonspherically distributed
valence electrons. The scattering of re-emitted positrons in PRM from atoms chemisorbed or physisorbed on the re-emitting
surface has not yet received the same theoretical attention as scattering from embedded atoms in LEPD. Possible ways in which
positron scattering from overlying atomic structures manifests itself in PRM as well as positron re-emission holography are
discussed, both from the practical viewpoint of observing these structures and in the context of fundamental questions regarding
the positron re-emission process itself. 相似文献
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For a simple model it is demonstrated that the Fano or conventional resonance occurs in systems with a two-level defect depending on the defect parameters. Conditions of the Fano and conventional resonance are analyzed. The problem of a system response to a stationary flux specified on the entire axis by a traveling wave has been solved. It has been found that this flux excites a quasilocal state in the continuous spectrum. Bands of amplitudes of the functions of system response to the stationary flux completely determine the quasilocal state spectrum. 相似文献