Atomic and molecular fluorescence with long radiative decay times from laser excited Na2

Na₂ is excited (B¹Π_u←X¹Σ _g ⁺ ) in the presence of noble gases (20–700 Torr). The Na₂ fluorescence decay shows two lifetimes: a short component which corresponds to the well known lifetime of Na₂ in the B¹Π_u state [1], and a long component with a lifetime of about 0,1 μs which depends strongly on the noble gas density [2]. The same long lived radiative decay is also seen via the Na resonance fluorescence Na(3²S)←Na(3²P).     

Perturbation-induced radiative decay of solitons

New results concerning emission of radiation (quasi-linear waves) from kinks described by various versions of a perturbed sine-Gordon equation are presented. Considered physical problems pertain to condensed matter physics and nonlinear optics. In perticular, intensities of Swihart wave emission from a fluxon in a long dc driven Josephson junction, and of spin wave emission from a domain wall in a weak ferromagnet driven by external constant magnetic field are calculated. A general estimate for an exponentially small intensity of emission from a kink oscillating near a bottom of an effective potential wall is obtained. A system of coupled double sine-Gordon equations describing a double DNA helix is briefly investigated. It is demonstrated that a collision of a bi-kink (a bound state of two 2Π-kinks belonging to different subsystems) with a 4Π-kink belonging to either subsystem may result in excitation of large-amplitude internal oscillations of both the colliding solitons, and the rate of radiative damping of those oscillations is found. At last, radiative effects accompanying motion of a stimulated-Raman-scattering soliton in a dissipative medium are studied.     

Weak radiative decay of baryons

The decay amplitudes and asymmetry parameters for weak radiative decay of baryons are calculated in both pole model and quark model. It is demonstrated that both models give the same results and the results satisfy the symmetry relations we have derived recently. The agreement of the theoretical prediction with the presently measured decay rates and asymmetry is quite good in view of uncertainty in the calculation.     

Fission and decay of excited nuclei

The statistical theory of the decay of excited nuclei including the competition between particle emission and fission is considered. Fission barriers are given by a phenomenological formula which is an analog of the known Cameron formula and approximates well experimental data on nuclei up to transuranic elements. The contribution of shell corrections and odd-even effects is discussed. The calculated ratios of evaporation and fission widths Γ_n/Γ_f agree with experiment even in the region of nuclei with Z > 90. The $\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}\text{Γ}{}_{\mathrm{<mtext>f</mtext>}}$ values depend weakly on excitation energy for nuclei with Z ≈ 90, While in other regions this dependence proves rather strong. The last conclusion does not contradict known experimental data since in experiments one usually measures some effective value $\text{〈}\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}\text{Γ}{}_{\mathrm{<mtext>f</mtext>}}\text{〉}$, which is only indirectly related to the real $\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}\text{Γ}{}_{\mathrm{<mtext>f</mtext>}}$, values. It is shown that the calculated values of $\text{〈}\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}\text{Γ}{}_{\mathrm{<mtext>f</mtext>}}\text{〉}$ depend on excitation energy either. The effects of angular momentum and uncertainty in the choice of level density parameter are discussed.     

Observation of the neutron radiative decay

The aim of this work is the experimental observation of and research into a rare neutron mode, the radiative beta decay, where a new particle, the radiative gamma quantum, is formed along with the expected decay products: a beta electron, a recoil proton, and an antineutrino. The discovery of this rare neutron decay mode was conducted through identification of triple-coincidence events: simultaneous registration of a beta electron, a proton, and a radiative gamma quantum. The ordinary neutron decay was registered by double coincidences of a beta electron and a recoil proton. The statistics collected allow one to deduce the branching ratio (BR) BR = (3.2 ± 1.6) × 10⁻³ (90% C.L.) in the gamma energy region greater than 35 keV. This value of BR is consistent with standard electroweak theory. The text was submitted by the authors in English. An erratum to this article is available at .     

类氢U91+离子的辐射复合及其辐射退激发过程的理论研究

基于多组态Dirac-Fock理论方法,利用GRASP92和RATIP以及在此基础上最新发展的RERR06程序,对类氢U⁹¹⁺（1s）离子的辐射复合截面以及辐射退激发过程进行了详细的理论研究.系统地计算了具有确定能量的连续电子被处于基态的类氢U⁹¹⁺（1s）离子俘获到nl （1≤n≤8, 0≤l≤6）轨道形成类氦U⁹⁰⁺（1snl）离子的辐射复合截面,并研究了这辐射复合末态退激发谱的相对强度.研究发现,类氢U⁹¹⁺（1s）离子辐射复合到不同轨道的截面随其主量子数的增大而显著减小;同时,辐射复合末态的退激发对Kα谱线的相对强度有重要影响. 关键词： 辐射复合 多组态Dirac-Fock理论方法 辐射退激发     

仿生辐射制冷的研究进展

辐射制冷是一种通过光谱调控来实现降温的新型制冷技术,相比于传统的主动制冷技术,如吸收式制冷、压缩制冷等,具有独特的优势,在环境保护和能源利用方面具有重要意义.本文首先从辐射制冷的基本原理出发,介绍了自然界中生物所具有的辐射降温特性.不同生物通过其材料、微观结构、行为等实现辐射制冷调控,为人类探究新型辐射制冷材料和器件带来了启发.本文也归纳了生物的辐射制冷机制,总结了生物结构的优化方法,并介绍了当前仿生辐射制冷的研究进展,对仿生辐射制冷的研究方向、应用前景和材料制备方法进行了展望.高功率、智能化的辐射制冷材料和器件是未来仿生辐射制冷的重要发展方向,先进微纳加工技术的融入将使仿生辐射制冷在未来具有更广阔的市场和应用.     

Neutrino radiative decay in external field and medium

The current state of the theory of massive neutrino radiative decay is reviewed. By extending our previous studies, we thoroughly analyze the process of radiative decay of a massive Dirac neutrino in the strong external magnetic field H ? H ⁰ = m _e ² c ³ / e? = 4.41 × 10¹³ G in the presence of medium (degenerate electron gas), and calculate its probability. It is shown that, in the presence of dense medium, the latter quantity becomes much larger than that in the magnetic field in the case of both relativistic and nonrelativistic neutrinos. Possible astrophysical applications of the obtained results are considered.     

L-shell ionization of atoms and their subsequent decay by radiative and non-radiative transitions

The study of the ionization of atoms resulting in vacancies in their inner shells and the subsequent decay of the atomic-vacancy states by x-ray and Auger transitions continue to be an active area of interest. A rapid survey of the theoretical efforts to calculate the transition probabilities involvingL-subshells in the high-Z atoms is presented. A complete review of theL ₁-subshell yields for single-vacancy atomic states obtained by various experimental techniques is included. The production of multiple vacancies in theL shell and the role of the spectator vacancies in the decay process is discussed. A detailed case study of determining experimentally the number of multiple vacancies produced, and the x-ray fluorescence yields during ionization by heavy-ion bombardment is presented. It is established that the effect of spectator vacancies is to increase the x-ray fluorescence yields substantially.     

Pole model for nonlepton and radiative hyperon decay

Nonlepton and weak radiative decays of hyperons are analyzed on the basis of the pole model. In contrast with other analyses, the contributions from both baryon and meson poles are taken into account. Experimental information on these decays is used to find the parameters of the effective weak two-baryon interaction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 17–22, August, 1969.The author thanks V. A. Filimonov and G. M. Radutskii for stimulating discission of this study.     

Demonstration of a collisionally excited optical-field-ionization XUV laser driven in a plasma waveguide

We describe the first demonstration of a collisionally excited optical-field-ionization laser driven within a waveguide. Lasing on the 4d(9)5d-4d(9)5p transition at 41.8 nm in Xe8+ was observed to be closely correlated to conditions under which the pump laser pulses were guided well by a gas-filled capillary discharge waveguide. Simulations of the propagation of the pump laser radiation show that gain was achieved over essentially the whole 30 mm length of the waveguide.