Determination of the effective cross sections for the excitation of the mercury metastable level 63P2

The deexcitation of the metastable mercury level 6³P₂ by electron impact was investigated by the method of impact of the second kind in a Hanle-type tube. These data and the relations of Klein and Rosseland were then used to reconstruct the excitation functiori for the 6S₀ 6³P₂ transition in mercury. A single maximum located 0.3 eV to the right of the excitation threshold was observed on the excitation function of the 6³P₂ level. A formula is also presented for the effective cross sections for the excitation of the mercury metastable 6³P₂ level. The effective cross section at the maximum of the excitation function of the 6³P₂ level is 2.9 · 10^–16 cm² ±30%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 85–91, December, 1970.The authors are deeply grateful to V. A. Fabrikant and the participants of the seminar under his direction for a discussion of the present results.     

Cross section of the reaction 6Li(p, γ)7Be

The cross section of the reaction ⁶Li(p, γ)⁷Be has been measured using Ge(Li) γ-ray spectrometers for proton bombarding energies E_p from 200 keV to 1200 keV. At E_p = 800 keV, the total (p, γ) integrated cross section is found to be 3.1 ± 0.4 μb. The cross section adopted from consideration of this and previous measurements is in good agreement with that predicted from the known thermal neutron cross section for ⁶Li(n, γ)⁷Li on the assumption that properties of mirror direct capture reactions can be well described by optical potentials that use the same parmeter values for the two reactions.     

Autoionization cross section of lithium atoms excited by electron impact

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn ₁ l ₁ n ₂ l ₂ detected at the “magic” observation angle of 54.7°. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 × 10⁻¹⁸ cm² in the energy interval of 56.4–60 eV and a subsequent monotonic drop to a value of 10⁻¹⁸ cm² at 600 eV. We have discovered a “thin” cross section structure that reflects the presence of strong resonances of Li⁻ ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s2)2S, (1s2s2p)⁴ P, 1s(2s2p ³ P)² P), and 1s(2s2p ¹ P)² P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4%. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.     

Inelastic collisions of the second kind between metastable mercury atoms and electrons

The experiments of Lattischeff and Leipunsku have been checked by a pulsed method under electron-beam conditions. The data were used to calculate the concentration of excited mercury atoms at the 6³P₀ level and to evaluate the effective cross sections for the excitation of inelastic collisions of the second kind. Our results are in good agreement with those reported by Fabrikant.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 11, pp. 63–66, November, 1968.In conclusion, the author Professor v. a. fabrikant for suggesting this topic.     

Photoionization cross section and oscillator strength distribution in the near-threshold region of strontium

We present experimentally measured absolute values of the photoionization cross sections from the 5s5p ¹P₁ and 5s5p ³P₁ excited states of strontium at the first ionization threshold as 11.4±1.8 Mb and 10.7±1.7 Mb respectively using saturated absorption technique along with a thermionic diode ion detector in conjunction with a Nd:YAG pumped dye laser system. These threshold photoionization cross sections values have been utilized to determine the oscillator strengths of the 5s5p ¹P₁↦5snd ¹D₂ and 5s5p ³P₁↦5snd ³D₂ Rydberg transitions. The oscillator strength densities in the continuum corresponding to the 5s5p ³P₁ excited state have also been determined by measuring the photoionization cross sections at five ionizing wavelengths above the first ionization threshold. Smooth merging of the discrete f-values into the oscillator strength densities has been observed for the 5s5p ³P₁↦5snd ³D₂ series across the ionization threshold.     

Measurements of photoionization cross sections from the 4p, 5d and 7s excited states of potassium

New measurements of the photoionization cross sections from the 4p ²P_1/2,3/2, 5d ²D_5/2,3/2 and 7s ²S_1/2 excited states of potassium are presented. The cross sections have been measured by two-step excitation and ionization using a Nd:YAG laser in conjunction with a thermionic diode ion detector. By applying the saturation technique, the absolute values of the cross sections from the 4p ²P_3/2 and 4p ²P_1/2 states at 355 nm are determined as 7.2±1.1 and 5.6±0.8 Mb, respectively. The photoionization cross section from the 5d ²D_5/2,3/2 excited state has been measured using two excitation paths, two-step excitation and two-photon excitation from the ground state. The measured values of the cross sections from the 5d ²D_5/2 state by two-photon excitation from the ground state is 28.9±4.3 Mb, whereas in the two-step excitation, the cross section from the 5d ²D_3/2 state via the 4p ²P_1/2 state and from the 5d ²D_5/2,3/2 states via the 4p ²P_3/2 state are determined as 25.1±3.8 and 30.2±4.5 Mb, respectively. Besides, we have measured the photoionization cross sections from the 7s ²S_1/2 excited state using the two-photon excitation from the ground state as 0.61±0.09 Mb.     

Cross section of supercooled238UF6 in multiphoton absorption induced by 16 micrometer Raman-laser radiation

Measurements of multiphoton absorption of 16 µm Raman-laser radiation in supercooled²³⁸UF₆ at 90 K were performed by using a pulsed Laval nozzle with an optical path length of 50 cm. The laser fluence was varied between 50 and 500 mJ/cm² for four frequencies in the range from 625 to 629 cm^–1. The energy absorbed by²³⁸UF₆ molecules was investigated as a function of laser frequency or fluence, and highly accurate results were obtained with the use of the nozzle whose optical path length is much greater than that of nozzles used before. The results indicated that the absorption cross section at the peak absorption frequency (627.8cm^–1) was proportional to the –1/3 power of the fluence.     

Action d'un champ magnetique sur le taux de polarisation de la raie interdite 2655,6 Å (61S0-63P0) du mercure

The forbidden radiation 2655.6 Å (6¹S₀-6³P₀) emitted by the odd isotopes of mercury is polarized in a magnetic field, even if the atoms are isotropically excited. The degree of polarization has been calculated for the case of ¹⁹⁹Hg. The experimental results agree with the theoretical predictions.     

锶原子三重态谱线的观测及在光钟中的应用

实验中通过互组跃迁689 nm激光抽运形成三重态最低能态原子布居,引入688 nm激光改变三重态最低能态间的原子布居,利用抽运光与探测光空间分离的方法观测碱土金属锶原子的三重态能态间跃迁(5s6s)³S₁ → (5s5p)³P_j(j=0,1,2)的吸收谱线,对应三条跃迁线的激光波段为679 nm, 688 nm和707 nm.探测三重态原子跃迁谱线可以用于锶原子冷却中再抽运光707 nm和679 nm激光频率的直接锁定,相比于通常利用的腔传递技术,可以把再抽运光频率锁定在原子跃迁谱线上,有利于提高锶原子冷却中俘获原子数目的长期稳定性.     

Resonances at collisions of slow electrons with cadmium atoms and ions

Using the crossed-beam method and a hypocycloidal electron spectrometer, the energy dependence of the ionization cross section for the cadmium atom has been studied in the near-threshold region and the elastic scattering of slow electrons at an angle close to 180° by Cd⁺ ions was studied for the first time. Within the region under study (0–7 eV above the first atomic ionization potential), a resonance structure determined by the contribution of atomic autoionization states is revealed in both the ionization curve and differential cross section of elastic scattering. The structure in the measured curves has been analyzed with the use of data on the ejected-electron spectra obtained under the excitation of autoionization states of Cd atoms, as well as the data on the optical excitation functions for the atomic spectral lines at λ=430.7 nm (5¹ P ₁-8¹ S ₀), 515.5 nm (5¹ P ₁-7¹ S ₀), 298.0 nm (5³ P ₂-6³ D _j ), and 361.0 nm (5³ P ₂-5³ D _j ).     

对汞亚稳态瞬态特性的研究

本文报道用脉冲光电流效应对Hg原子在低压放电中亚稳态6³P_0.2和第一共振态6³P₁衰减机制的研究。指出亚稳态原子间的碰撞电离、再复合及二极扩散过程是这种缓慢衰减的主要因素。实验测定了在不同温度下6³P_0,1,2态的平均有效寿命及扩散系数。实验结果与理论计算相符。由于6³P_0,1,2态在Hg放电中的关键作用,这种灵敏、简便和干扰小的 关键词：     

一种考虑几何屏蔽效应的计算“电子-分子”散射总截面的可加性规则修正方法

在考虑分子内原子间的几何屏蔽效应随电子入射能量变化的基础上, 提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的可加性规则修正方法. 利用这一修正后的可加性规则并使用“电子-C, H, O, N原子”散射总截面的实验数据, 在50—5000 eV内计算了电子被NO, N₂O, NO₂和C₂H₆分子散射的总截面, 且将计算结果与实验结果及其他理论结果进行了比较. 结果表明, 利用这一方法修正过的可加性规则进行计 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

Inelastic collision cross section of excited molecules

The (v′=6,J′=43) level in theB ¹Π _u electronic state of Na₂ has been selectively populated by excitation with the 4 880 Å line of the argon laser. Through collisions with He atoms energy is transferred to neighbouring rotational states in Na₂ and the density of these states is determined by observing fluorescence to electronic ground state. From previous measurement of the lifetime of theB ¹Π _u state and new measurements of the intensities of collision induced spectral lines as a function of He pressure, absolute collision cross sections for all rotational transitions up to ΔJ=±5 have been obtained. The total cross section for all rotational transitions observed is σ _rot ^total =65±15 Ų. Preliminary results about collision induced vibrational transitions are also presented.     

Autoionization cross section of potassium atom excited by electron impact

The autoionization cross section of potassium atoms excited by electron impact is measured in the energy range from the first autoionization threshold at 18.72 eV to 202 eV. The data are obtained by deter-mining the total intensity of electron spectra resulting from the decay of the 3p ⁵ n ₁ l ₁ n ₂ l ₂ autoionizing states. The cross section has two maxima, 1.8 × 10^?16 and 2.2 × 10^?16 cm², at 21 and 32 eV, respectively. The excitation dynamics of autoionization states suggests that the first maximum is associated with the resonance character of the near-threshold excitation. The second maximum, as well as the behavior of the cross section at energies above 50 eV, reflects the dynamics of electron excitation of quartet and doublet autoionizing states. The measured autoionization cross section is compared with known data for the total single ionization cross section of potassium atom by electron impact. The relative contribution of the autoionization cross section to the total single ionization cross section is found to reach 30% at 32 eV.     

The 12C + 12C sub-coulomb fusion cross section

The ¹²C + ¹²C fusion cross section has been studied over the energy range 2.46 ≦ E_c.m. ≦ 5.88 MeV. The yields of the γ-rays emitted from the first excited states of ²³Na and ²⁰Ne, following ²⁴Mg compound nucleus decay via proton- and α-emissions, were measured using a Ge(Li) detector. The fusion cross section was obtained by normalizing these yields to previously reported ¹²C(¹²C, p)²³Na and ¹²C(¹²C, α)²⁰Ne cross sections. The data indicate that the cross section below 3.5 MeV is dominated by two or more resonances, and that the average trend in this energy region does not show the absorption-under-the barrier features of the optical model. For astrophysical extrapolations to lower energies, the new results are consistent with the extrapolation proposed by Fowler, Caughlan and Zimmerman.     

一种计算中、高能电子被分子散射总截面的修正势方法

在考虑分子内成键原子间的电子云重叠效应的基础上，提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的修正势方法.利用可加性规则及Hartree-Fock波函数，使用这一修正过的复光学势，在30—5000eV内对电子被4个等电子(Z=18)分子(HCl，H₂S，PH₃和SiH₄)散射的总截面进行了计算，并将理论计算值与实验结果及其他理论值进行了比较.结果表明，利用这一修正过的复光学势及可加性规则进行计算，所得理论值与实验结果更为接近. 关键词： 电子散射 总截面 可加性规则 束缚原子     

Optogalvanic detection of velocity-selective optical pumping in an open, cascade atomic medium

We performed two-color spectroscopy of the (4s²) ¹S₀ → (4s4p) ¹P₁ → (4p²) ¹D₂ calcium atomic transition and observed velocity-selective optical pumping in a calcium hollow cathode lamp by means of optogalvanic detection. The optical pumping signature in optogalvanic detection is compared to that of fluorescence and transmission detections. The optogalvanic technique is found to be a very sensitive method of detecting optical pumping and could be used in distinguishing optical pumping from electromagnetically induced transparency.     

Radiative transitions in the system of autoionizing levels of cesium atoms excited by electron impact

We study the energy dependences of electron excitation cross sections of the autoionizing levels (5p ⁵6s ²)² P _3/2 and (5p ⁵5d(³ P)6s)² P _3/2, as well as the autoionization cross sections of cesium atoms in the impact energy range from the excitation threshold to 600 eV. It is established that an increase in the excitation cross section of the ² P _3/2 levels (to 60% of the maximum value) and the deep minimum in the autoionization cross section observed in the energy region of 17–27 eV are caused by the predominance of the radiative decay channel for autoionizing levels with excitation thresholds above 17 eV. The high efficiency of the process is mainly related to the resonance excitation of these levels in the near-threshold energy region.     

Photoionization cross section of Ne-like Cu XX with J=1

Relativistic calculations of photoionization cross sections of Ne-like Cu XX using the Breit–Pauli R-matrix method in close-coupling approximation and fully relativistic distorted-wave method are reported. In the present work, the relativistic distorted-wave method is employed to calculate the fine-structure energy levels and radial functions, and the Breit–Pauli R-matrix method is employed to calculate photoionizaton cross section for photon energy from 124.2 Ryd to 208 Ryd. Resonance structure in the photoionization of Ne-like Cu XX for ejection of 2p or 2s electron from the ground 2s²2p^{6 1}S₀ has been studied.     

Raman scattering cross section and density measurements of UF6

We have applied laser Raman scattering to the measurement of the density of UF₆ vapor. A linear relation between scattering intensity and density is shown. We have also measured the absolute Raman scattering cross section of the 665 cm⁻¹ line of UF₆ by the substitution technique and obtained a value of 1.02±0.09×10⁻²⁹ cm²/sterad at 488 nm. Measurements of the line position and the depolarization ratio of this line are also reported. Work supported by the U. S. Energy Research and Development Administration.