Neutron Moderation Theory Taking into Accout the Thermal Motion of Moderating Medium Nuclei

In this paper we present the analytical expression for the neutron scattering law for an isotropic source of neutrons, obtained within the framework of the gas model with the temperature of the moderating medium as a parameter. The obtained scattering law is based on the solution of the kinematic problem of elastic scattering of neutrons on nuclei in the L-system in the general case. I.e. both the neutron and the nucleus possess the arbitrary velocity vectors in the L-system. For the new scattering law the flux densities and neutron moderation spectra depending on the temperature are obtained for the reactor fissile medium. The expressions for the moderating neutrons spectra allow reinterpreting the physical nature of the underlying processes in the thermal region.Comment: 26 pages, 6 figure

Ultraslow Wave Nuclear Burning of Uranium-Plutonium Fissile Medium on Epithermal Neutrons

For a fissile medium, originally consisting of uranium-238, the investigation of fulfillment of the wave burning criterion in a wide range of neutron energies is conducted for the first time, and a possibility of wave nuclear burning not only in the region of fast neutrons, but also for cold, epithermal and resonance ones is discovered for the first time. For the first time the results of the investigation of the Feoktistov criterion fulfillment for a fissile medium, originally consisting of uranium-238 dioxide with enrichments 4.38%, 2.00%, 1.00%, 0.71% and 0.50% with respect to uranium-235, in the region of neutron energies 0.015-10.0eV are presented. These results indicate a possibility of ultraslow wave neutron-nuclear burning mode realization in the uranium-plutonium media, originally (before the wave initiation by external neutron source) having enrichments with respect to uranium-235, corresponding to the subcritical state, in the regions of cold, thermal, epithermal and resonance neutrons. In order to validate the conclusions, based on the slow wave neutron-nuclear burning criterion fulfillment depending on the neutron energy, the numerical modeling of ultraslow wave neutron-nuclear burning of a natural uranium in the epithermal region of neutron energies (0.1-7.0eV) was conducted for the first time. The presented simulated results indicate the realization of the ultraslow wave neutron-nuclear burning of the natural uranium for the epithermal neutrons.Comment: 35 pages, 19 figures (v2: Fig12 and some misprints in the text are fixed

Исследование влияния герметизации многорупорного приемо-передающего облучателя на его характеристики

One embodiment of a multi-horn waveguide irradiator is a structure consisting of flat interconnected plates having a metallized surface or made entirely of metal with high electrical conductivity. Important characteristics of the receiving-transmitting irradiator are the voltage standing wave ratio at its input and output, as well as the decoupling of the transmitting and receiving channels. When using the antenna system in difficult climatic conditions, it is necessary to ensure the tightness of the irradiator. To do this, it is necessary to eliminate the possibility of moisture penetration inside the waveguide channels through the open apertures of the horn radiators and through the joints of the parts. Sealing of the irradiator horns can be performed by closing their apertures with a film of radiolucent material. To reduce the effect of such a shelter, the thickness of the film should be minimal and be chosen sufficient to provide mechanical strength. When using a multi-horn irradiator in a transceiver system operating on waves with circular polarization of an electromagnetic field, using a mutual polarizer and a polarization selector in the channel of each horn can provide decoupling of the transmission and reception paths of the irradiator. The introduction of a sealing film into the aperture of the irradiator increases the reflection of electromagnetic waves in its radiators, which causes  deterioration in the decoupling of the transmitting and receiving channels of the irradiator. A possible option to ensure the tightness of joints of metal parts of the irradiator design is their soldering. A significant disadvantage of this sealing method is the possibility for the solder to flow into the internal waveguide channels of the irradiator. This can cause an increasing reflection of the electromagnetic waves in the paths of the irradiator and a deterioration of the decoupling of the transmitting and receiving channels. The sealed methods considered were tested on a waveguide four-horn irradiator of the Ka-band of frequencies. The research has shown that the application of the described methods of sealing the multi-horn irradiator allows maintaining high values of the channel decoupling and acceptable matching of its inputs.Одним из вариантов выполнения многорупорного волноводного облучателя является конструкция, состоящая из плоских соединяемых между собой плит, имеющих металлизированную поверхность или изготовленных целиком из металла с высокой электрической проводимостью. Важными характеристиками приемо-передающего облучателя являются коэффициент стоячей волны по напряжению на его входе и выходах, а также развязка передающего и приемных каналов. При использовании антенной системы в сложных климатических условиях необходимо обеспечить герметичность облучателя. Для этого нужно устранить возможность попадания влаги внутрь волноводных каналов через открытые раскрывы рупорных излучателей и стыки деталей. Герметизация рупоров облучателя может выполняться путем закрывания их раскрывов пленкой из радиопрозрачного материала. Для снижения влияния такого укрытия толщина пленки должна быть минимальной и выбирается достаточной для обеспечения механической прочности. При использовании многорупорного облучателя в приемо-передающей системе, работающей на волнах с круговой поляризацией электромагнитного поля, разделение передающего и приемных трактов облучателя может обеспечиваться применением взаимного поляризатора и селектора поляризации в канале каждого рупора. Введение герметизирующей пленки в раскрыв облучателя увеличивает отражение электромагнитных волн в его излучателях, что вызывает ухудшение развязки передающего и приемных каналов облучателя. Возможным вариантом обеспечения герметичности стыков металлических деталей конструкции облучателя является их пропайка. Существенный недостаток этого способа герметизации заключается в возможности затекания припоя во внутренние волноводные каналы облучателя. Это может стать причиной увеличения отражения электромагнитных волн в трактах облучателя и ухудшения развязки передающего и приемных каналов. Рассмотренные способы герметизации испытаны на волноводном четырехрупорном облучателе Ка-диапазона частот. Исследования показали, что применение описанных способов герметизации многорупорного облучателя позволяет сохранить высокие значения развязки каналов и приемлемое согласование его входов

Orbital forcings of the Earth?s climate in wavelet domain

International audienceWe examine two paleoclimate proxy records ? the temperature differences from the Antarctic Vostok ice core and the composite ?18O record from three sites (V19-30, ODP 677, and ODP 846) ? in order to search for indications of orbital forcings. We demonstrate that the non-decimated wavelet transform is an appropriate tool for investigating temporarily changing spectral properties of records. Our results indicate that abrupt climate warmings with cyclicity of ~100 kiloyears during the last 400 kiloyears were caused by the combined unidirectional influences of three orbital parameters and the eccentricity can be considered as a modulator defining transitions from the Ice Ages to the periods of comparative warmings. Non-decimated wavelet transform avails discovering the possible part played in climate change by the eccentricity-forced variations. Up to approximately 1.7 million years BP, the influence of this variations of eccentricity appears in increasing for almost all local maxima of ?18O. Since the ~1.7 million years BP, minor and significant maxima alternated and this not affected as much the variations of ?18O