Attenuation of pile neutron flux in polyethylene

The relaxation lengthsofresearch reactor neutrons were measured in polyethyIene. The findings are in excellent accord with data computed theoretically using the method of moments. The relaxation lengths are 15% less than in the case of water.Translated from Atomnaya Énergiya, Vol. 15, No. 1, pp. 17–20, July, 1963     

Averaging the neutron diffusion equation

This paper presents a general theoretical analysis of the neutron motion problem in a nuclear reactor, where large variations on neutron cross-sections normally preclude the use of the classical neutron diffusion equation. A volume-averaged neutron diffusion equation (VANDE) is derived which includes correction terms to diffusion and nuclear reaction effects. A method is presented to determine closure-relationships for the VANDE (e.g., effective diffusivity). In order to describe the distribution of neutrons in a highly heterogeneous configuration, it was necessary to extend the classical neutron diffusion equation. Thus, the averaged diffusion equation includes two correction factors: the first correction is related with the absorption process of the neutron and the second correction is a contribution to the neutron diffusion, both parameters are related to neutron effects on the interface of a heterogeneous configuration. As an example of the VANDE, the plane source in an infinite medium was considered to study the effects of the correction factors on the neutron flux, and the results were compared with classic solution.     

The thermal neutron induced fission cross-section of Am

The σ(n_th,f) of ²⁴³Am has been measured using the cold neutrons with a 25 K Maxwellian distribution available at the Grenoble high flux reactor. Surface barrier detectors recorded the fission fragments. A value of σ(n_th,f) = (198.3 ± 4.2)mb was obtained for ²⁴³Am relative to σ(n_th,f) = (582.2 ± 1.3)b for ²³⁵U.     

Calculation of neutron diffusion in periodic lattices

Tile article describes a method for calculating neutron diffusion in heterogeneous periodic lattices; the method requires solution of the transport equations only within one cell. For simplicity, a onedimensional lattice is considered in the diffusion approximattonl however, the boundary conditions and the method of obtaining the exact solution are sufficiently general for the entire medium. In addition to the actual solution for the entire medium, the macroscopic (averaged) solution is also given, so that the homogenization of the medium becomes easy and natural. The conditions under which homogenization is possible are also explained.The method is applicable both to multiplying and nonmultiplying media, as well as to media with independent sources.Translated from Atomnaya Énergiya, Vol. 13, No. 6, pp. 556–562, December, 1962     

The study of neutron diffusion in beryllium by a pulse method

A pulsed-neutron-source method was used to determine to a high accuracy the diffusion and nuclear characteristics of beryllium: the diffusion coefficient, the diffusion and transport lengths, the mean lifetime, the effective absorption cross section, and the diffusion-cooling coefficient.The article discusses the reasons for the discrepancies between the values obtained by different authors for the diffusion-cooling coefficient.Translated from Atomnaya Énergiya, Vol. 16, No. 3, pp. 224–228, March, 1964     

离子束混合中的扩散、热扩散与化学反应效应

离子束混合的理论研究目前集中在混合机制。已提出的机制主要有碰撞级联混合与辐射增强扩散混合。在文献[5、6]中我们给出了这两种机制统一处理的模型与数学表述。     

Lattice diffusion coefficient of oxygen in lithium oxide

Lattice diffusion coefficients of the oxygen ion in antifluorite-cubic Li₂O were determined employing polycrystalline samples, in the temperature range of 920 ~ 1130°C, by means of the gas-solid isotope exchange and solid-phase analysis technique; use was made of the relationship between the particle-size and grain-size dependences of the grain-boundary enhanced diffusion. The results were described by D = 1.52 × 10³ exp$\text{(?83.3 × 10}{}^3\text{/RT)}\text{cm}{}^2\text{s}$ and showed a good agreement with the previously reported results determined by the gas-phase analysis technique. Diffusion characteristics of the constituent ions in the antifluorite-cubic structure were discussed in comparison with those in fluorite-cubic crystals.     

Effective boundary conditions in the theory of neutron diffusion

In this review, a method of determining effective boundary conditions (EBC) is described which guarantees the asymptotic agreement of the solution of the neutron diffusion equation with the solution of the corresponding kinetic equation. For monoenergetic neutrons, the EBC are considered for plane and cylindrical surfaces of black and gray bodies. Results are given for the EBC for the case of cylinders of arbitrary section.The authors discuss the simplest problem in the determination of EBC for neutrons that are slowed-down in a medium with heavy atoms and with an energy-independent cross section. The review gives also results obtained by various authors in the USSR and in other countries.     

On multi-media calculations in the theory of neutron diffusion

The F_N method is used to solve the critical problem for a three-region reactor and to compute the disadvantage factor required for thermal utilization calculations. Anisotropic scattering is allowed and numerical results are given.     

氡及其子体水平扩散系数测量研究

氡气运移的研究成果表明,氡气的运移具有方向性。本文从实验入手,采用静态、累积、高灵敏度的测氡方法,对氡累积水平扩散分布进行了测量。采用最小二乘法拟合方法对不同温度条件下氡及其子体的水平扩散系数进行了计算。实验研究结果表明,氡及其子体的水平扩散系数与温度的相关系数为0.92,两者呈线性正相关关系;在恒温(30℃)条件下的实测水平扩散系数为0.049cm2·s-1;要使氡在空气中的水平扩散系数达到经典值0.1cm2·s-1,其环境温度应达到40℃以上。