Experimental Studies of Radiation-Protective Properties of a Modified Titanium Hydride

The results of experimental studies of the protective properties of titanium hydride with respect to neutron and gamma radiation in order to determine the optimal conditions for their use in the composition of the structural radiation protection of the nuclear reactor are presented. The weakening of the basic functionals in the thickness of protection, including the density of fast, intermediate and thermal neutrons, and the dose rate of gamma radiation is established. The functions of weakening the density of neutron flow and the dose rate of gamma radiation are measured in the conditions of "barrier" geometry. Determination of the protective properties of the structure was carried out when the modified titanium hydride fraction was placed in aluminum containers with a filling coefficient of a volume of container 0.63. The relaxation lengths for all neutron groups are close and on average are 9.8 cm. The functions of weakening the dose rate of gamma radiation of point sources Cs-137 and Co-60 are exponential. The weakening of radiation occurs with a constant relaxation length. For energy 0.661 MeV, the relaxation length is 7.1 cm, for energy 1.25 MeV, the relaxation length is equal to 10.1 cm. On the basis of the experimental studies, the high efficiency of the modified fraction of titanium hydride was confirmed during its use in protecting nuclear power plants.

Assessment of Radiation Shielding Properties of Polymer-Lead (II) Oxide Composites

Long term exposure to very high levels of radiations from medical diagnostic centres, industries, nuclear research establishments and nuclear weapon development have resulted in health effects such as cancer and acute radiation syndrome, hence the need for proper radiation shielding. This paper investigated Epoxy-Lead (II) Oxide (PbO) composite as radiation shielding. The composites were prepared by dispersion of microsized PbO particles into polymeric materials using effective melt-mixing method and cast in a 4 cm by 6 cm rectangular aluminium Mold with a thickness of 5 mm and was allowed to set over night at room temperature. The gamma ray attenuation ability of the composites were studied using gamma ray transmission or attenuation coefficient determination for the gamma ray energy. Three gamma ray sources Ba-133, Cs-137 and Co-60 were employed. The density, linear attenuation coefficient, half value layer (HVL), relaxation length and heaviness of the samples were determined. The measured values of linear attenuation coefficient increased with increasing filler concentration in all the samples at all gamma ray energies. It was also noticed that 40 % and 50 % filler samples attenuates more relative to the other samples under study. The maximum linear attenuation attained was found at energy of 662 keV. The composites have been found to possessed medical gamma-ray attenuation characteristics among the sample materials over a certain photon energy range (0.08 MeV–1.332 MeV) and found useful as a biological radiation shielding against gamma rays.

Direct measurement of magnon temperature by magneto-optic Kerr effect in YIG

Magnon-phonon thermal relaxation holds a fundamental role in condensed matter physics, and the difference between local phonon and magnon temperature ΔTmp as an important part of this subfield was theoretically considered responsible for the spin Seebeck effect. Experimental determination of ΔTmp is necessary to give more insight into magnon-phonon coupling. Here we report spatially resolved measurements of magnon temperature performed by magneto-optic Kerr effect in yttrium iron garnet. Our results indicate a strong interaction between magnon and phonon subsystems in YIG with an upper limit of the phonon-magnon thermal relaxation length of 1.4 mm, and means this method is valid.

Kinetic Description of Propagation of Quasiparticles Fluxes in Solid-state Structure

Within the framework of the kinetic theory, the interaction of systems of quasiparticles and the exchange of quasiparticles of different types between layers of a plane-parallel solid structure are taken into account. The reasons influencing the propagation of differential fluxes of quasiparticles near each boundary of the structure are indicated. These include not only the appearance of a force field, in particular, electric е∇φ(х) and thermal ∇Т(х), fields near the boundary in equilibrium and its modification when equilibrium is disturbed, but also a change in the coordinate and angular dependence of the relaxation length of fluxes le(x, k, Ω) in the same region. Some modification of the distribution of characteristic thermodynamic quantities in the inhomogeneous region of the layer in comparison with the homogeneous layer also affects the propagation of fluxes. The necessity of a self-consistent solution of the kinetic boundary value problem of the joint propagation of differential fluxes of quasiparticles-a system of equations and integral boundary conditions-is substantiated. Near the boundary and in another inhomogeneous region of the layer thickness, as well as in the thin layer as a whole, in quasiparticles systems, it is proposed to use a specific coordinate distribution of the flux density of thermodynamic quantities over the structure thickness, which is mutually self-consistent with the propagation of the corresponding quasiparticles fluxes. The main conclusion of this work: when developing modern multilayer solid-state structures, especially with thin layers, it is necessary to use the kinetic theory, which adequately takes into account the physical picture that occurs not only in homogeneous and inhomogeneous regions of the thickness of each layer, but also at all boundaries of the structure.

Wheel Speed Effect on Transient Lateral Force and Its Characterization by Ramp-Step Steer Test Method

ABSTRACT The concept “relaxation length” serves as one of several ways to characterize the transient lateral response for a rolling tire. Most test methods developed to identify relaxation length tightly link to Pacejka's single-contact-point linear transient model. Its underlying assumption is that the traveled distance during the transition interval is always a constant regardless of the wheels' linear rolling speed. The current research provides physical data against this strong assumption. The data is acquired through a newly-developed test method named the “ramp-step steer method”. The ramp-step steer method features a nonstop, high rolling speed, and fast-changing slip angle procedure that cannot be fulfilled by the conventional “start-stop-resume” step steer method. Thanks to the high dynamic capability of the equipment in GCAPS Corp., the proposed test method becomes feasible. A novel data postprocessing scheme accompanies the test method as well. The ramp-step steer method is independent of any specific models and replicates the scenario of a rolling tire subjected to a sudden slip angle change from on-vehicle to an indoor environment. The wheel speed effect on the tires' transient lateral response is reflected through a proposed quantity, Ly, which is a more general descriptor and can downscale to relaxation length under specific circumstances. Ly itself does not associate with any model, so the remaining study explains the speed effect through an updated model. The present research aims to provide a better way of characterizing tires' lateral transient behavior and is not an alternative to identify the key parameter “relaxation length” in Pacejka's model. Another contribution of the research is categorizing and separating the hierarchy of various transient tire models.

Using Plasma Etching to Access the Polymer Density Distribution and Diffusivity of Gel Particles

In this paper we examine the polymer density distribution of gel particles and its effect on solvent diffusivity through the polymer network. In order to access the inner particle regions, external polymer layers were removed by plasma etching, thus reducing them from the outside. Higher polymer densities after erosion showed internal heterogeneity, with the density increasing towards the center of the particles. An exponential decay polymer density model is proposed, and the spatial relaxation length measured. The diffusion of solvent through the particles, before and after the plasma oxidation, revealed a correlation between the diffusion coefficient and the internal density.

MULTI-GROUP MODELING OF PROTECTION AGAINST NEUTRON AND GAMMA RADIATION BY MATERIALS BASED ON TITANIUM HYDRIDE

The paper provides a comparative calculation of the radiation protective efficiency of various composite materials based on titanium hydride using multi-group modeling methods using the ANISN program. The calculations showed the high efficiency of titanium hydride composites with respect to neutron and gamma radiation. The relaxation length of the fast neutron flux density in titanium hydride materials is 5.1…7.0 cm. The spatial-energy distribution of neutron radiation in materials is formed by fast neutrons. The dose rate of gamma rays behind the material is determined mainly by capturing gamma rays arising in the initial layer of protection. Introduction to the composition of the protection of boron atoms reduces the level of capture gamma radiation, but does not affect the attenuation of fast neutrons.

CONTAMINATION DEPTH OF 137CS IN CONCRETE STRUCTURES

Uncertainty analysis for nondestructive estimation of contamination depth is presented. The contamination depth was determined using the peak-to-peak method as an in-situ measurement in which gamma spectra were measured by an HPGe detector. Since exponential activity distribution is a crucial assumption of this method, the distribution profile was confirmed by laboratory tests of core drill samples. The main parameter influencing uncertainty of contamination depth is uncertainty of relaxation length. The uncertainty is composed for statistical error represented by the ratio of net peak areas and systematic error given detection efficiency of measurement setup. Systematic relative error was evaluated to be 7.45%. Statistical relative error was evaluated to 9.97% for the proposed optimum net peak area. Variability of relaxation length was identified to be very low with mean value 2 mm with standard deviation 0.73 mm. For fixed relaxation length, it should be possible to estimate contamination depth by nonspectrometric devices.

Effects of Different Tire Operating Conditions on Transient Lateral Tire Response

ABSTRACT The concept of the relaxation length is often used to describe a tire's transient response. This paper investigates how the transient response changes under different operating conditions. Through the measurement of tire forces and tire deformations during transient maneuvers performed on an indoor flat-belt tire test machine, experimental data were used to calculate various tire stiffnesses and the associated relaxation lengths using a novel method via optimization. With this methodology, the effects of tire load, inflation pressure, speed, and temperature on these stiffnesses and the relaxation length have been identified. The mechanisms behind these effects are discussed with a particular focus on the influence of temperature.