Relative Yield and Period of Individual Groups of Delayed Neutrons in 233U, 235U, and 239Pu Fission by Epithermal Neutrons

The relative yield of delayed neutrons and the half-life of their precursor nuclei in fissioning of ²³³U, ²³⁵U, and ²³⁹Pu by epithermal neutrons are measured on a setup which is based on a KG-2.5 electrostatic accelerator. The experimental samples are irradiated in a polyethylene cube, one face of which is irradiated by a neutron beam consisting of T(p, n)³He neutrons. A procedure is developed for averaging the group parameters of delayed neutrons from different series of measurements, taking account of their correlation. A comparative analysis of the data of this work and in ENDF/BVI in terms of the average half-life of the precursor nuclei of the delayed neutrons and using the dependence of the reactivity on the asymptotic period of the reactor is performed.It is shown that the data of this work agree, to within the uncertainty limits, with the recommended experimental data and differ substantially from the ENDF/BVI data.     

A Method of Measuring Current–Voltage Characteristics Based on the Hammerstein–Chebyshev Model

A method of measuring the current–voltage characteristics of nonlinear components is proposed, which involves applying a sinusoidal voltage to the object being measured, finding the Fourier spectrum to read out the output current, and a calculation using the spectrum of the coefficients of the expansion of the measured characteristic in Chebyshev polynomials. The properties of the Hammerstein–Chebyshev model are considered, a block diagram of a measuring instrument is presented, and recommendations are made for minimizing the systematic errors due to approximating their characteristics by Chebyshev polynomials.     

Relative yield of delayed neutrons and half-life of their precursor nuclei with fissioning of 239Pu by 14.2–17.9 MeV neutrons

The energy dependence of the relative yield of delayed neutrons and of half-lives of their precursor nuclei with fissioning ²³⁹Pu by 14.2–17.9 MeV neutrons is measured. The data obtained are analyzed in terms of the average half-life 〈T〉 of the precursor nuclei of the delayed neutrons. It is shown that the observed growth of 〈T〉 with increasing primary neutron energy in the energy range studied is due predominately to opening of the channels for the emission fission of nuclei. Comparing the data on the average half-life of the precursor nuclei of delayed neutrons obtained in the present work with those obtained by other authors showed that the anomalously high values of 〈T〉 are due to methodological features of the experiment which are related with the properties of the reaction T(d, n)⁴He used as a neutron source on electrostatic charged-particle accelerators. The data obtained are of great value for developing instrumentational nondestructive means for determining the nuclide composition of nuclear fuel based on the detection of delayed neutrons. __________ Translated from Atomnaya énergiya, Vol. 101, No. 6, pp. 441–444, December, 2006.     

The structure of Alu-like DNA nucleotide sequences in cyclostomes and fishes

By methods of DOT hybridization and polymerase chain reaction (PCR) structures similar to Alu repeats were shown in the genome of fish and lamprey. The fact of the presence of such sections in representatives of many orders of fishes, and also our experimental data allow to suppose that Alu-like structures, similar to 3' region of Alu repeats on mammals, have been already formed in these. The evolutionary significance of described structures has been supposed.     

Use of the Laws of Delayed Fracture of Metallic Materials for Forecasting the Remaining Life of Structures under a Test Load

Metal Science and Heat Treatment -     

New Concepts Accounting for Variations in the Formation of Multilayer Fiber Composite Materials

Fibre Chemistry - Changes in the mechanical properties of fibrous composite materials can be largely explained by quantitatively evaluating variations in the formation of their macro- and...     

Effect of the Loading Rate on the Microhardness of Metallic Materials and the Micromechanism of Plastic Strain

Metal Science and Heat Treatment -