Particle systems with variable length

We present a new class of one-dimensional particle systems, in which the number of components may change in the process of interaction. We suggest that some of these systems display spontaneous symmetry breaking. Received: 16 August 2002     

Cosmic history of some pallasites based on fossil track studies

Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Examination of fossil charged-particle tracks in the phosphate and olivine crystals of 5 pallasites coupled with U content determination allowed the estimation of the contributions of all possible track sources to the total track density and calculation of a value of model fission-track age.

Phosphate crystals from all studied pallasites were established to contain fossil tracks due to galactic cosmic rays (VH, VVH nuclei); induced fission of U and Th by cosmic rays; spontaneous fission of ²³⁸U; spontaneous fission of extinct short-lived ²⁴⁴Pu nuclei presented in significant quantities in the early solar system. The discovery of a high track density attributed to the extinct ²⁴⁴Pu pointed obviously to the high value of the fission-track age. Model fission-track ages of (4.37±0.02) Gyr for the Marjalahti pallasite; (4.37±0.01) Gyr for the Omolon pallasite; (4.19±0.02) Gyr for the Bragin pallasite; (4.18±0.03) Gyr for the Krasnoyarsk pallasite; (4.21±0.02) Gyr for the Brenham pallasite were calculated. The comparison of represented data with petrographic analyses allowed us to interpret a value of fission-track age as the time of the last intensive shock/thermal event in the cosmic history of a pallasite.     

Search for the ternary cluster decay of Cm isotopes using SSNTD

Investigation of the ²⁴⁶Cm spontaneous ternary decay into nearly equal clusters using polyethyleneterephthalate track detectors has been carried out. The possibility of ternary cluster decay has been found out to be of less than 10⁻⁶ with respect to all fission modes of ²⁴⁶Cm.     

Application of quartz glass tubes as the track detectors for chemical identification of short-lived isotopes of elements 104, 105 and 106

The quartz glass open chromatographic columns with thermal gradient, which usually were used for the investigation of chemical properties of short-lived Z104 nuclides, were first used as the track detectors of spontaneously fissioning isotopes of elements 104, 105 and 106. The recoil nuclei of these elements were captured by the flow of gaseous chlorides then go to the quartz tube with reducing thermal gradient 400°C-100°C. The quartz tube was etched in 40% HF. The tracks due to spontaneous fission of isotopes ²⁵⁹104, ²⁶²105 and ²⁶³106 which were etched at the internal wall of quartz tubes were counted under optical microscope.     

1313nm脉冲泵浦下掺Er3+光纤中多波长可见光的产生

本文报道了以1313nmNd:YLF激光脉冲泵浦掺饵(Er³⁺)单模GeO₂/SiO₂光纤而产生多波长可见光的实验,在该光纤中观察到(463～510)nm间的多波长放大自发辐射过程,此过程对应于Er³⁺离子的²G_7/2等几个激发态到⁴I_13/2亚稳态的跃迁.其激发过程是分步的四光子吸收过程,同时,掺饵光纤的红外发射峰1530nm(⁴I_13/2-⁴I_15/2)与1313nm泵浦光之间的三波混频过程也对这一区间的连续多峰的光谱结构有贡献.实验中还观察到540nm附近的绿光辐射.     

Superradiance of trapped atoms

A new method for calculating the total power of the spontaneous emission of a few motionless two-level atoms located at a distance of the order of the resonance-radiation wavelength with dipole-dipole interaction is suggested. The method is based on the Schrödinger representation. It is shown, as an example, that two trapped atoms cannot emit a pulse of superradiance under any conditions, while four atoms can emit such a pulse at certain conditions. Different ways of introducing the quasi-stationary states of atoms along with the generalization of the proposed method to other resonance systems are discussed.     

准分子激光放大器中的三维放大自发辐射效应

发展了小纵横比条件下、具有圆柱对称性介质的高功能ＫｒＦ准分子激光放大器中，放大自发辐射效应的三维理论模型和计算程序。考虑自发辐射的频率分布效应以及侧壁表面反射效应。结果分析表明，当纵横比及入射负载均较小时，放大自发辐射对输出光束质量有较大的影响。     

Spontaneous magnetization of the Ising model on a layered square lattice

We have studied the Ising model on a layered square lattice with four different coupling constants and two different magnetic moments. The partition function at zero magnetic field is derived exactly. We propose a formula for the spontaneous magnetization which agrees with the exact low-temperature series expansion up to the 16th order and reduces to the exact result of Au-Yang and McCoy in a special case.