Results 1 - 10 of 12609
Results 1 - 10 of 12609. Search took: 0.037 seconds
|Sort by: date | relevance|
[en] The radiation attenuation coefficients μ/ρ (cm2 g-1) for concrete and cement samples that used for experimental studies by other researchers were determined by Monte Carlo calculations at 59.5, 80, 356, 661.6, 1173.2 and 1332.5 keV photon energies. The simulated results of attenuation coefficients were compared with the reported experimental data for the same samples and a good agreement has been observed. The intent of this research was to develop a Monte Carlo program useful for various absorbers and energies. The variation of the attenuation coefficient with photon energy has also been investigated for these samples. (author)
[en] The intensity of radio waves received by radio telescopes is always not subject to human control. In the millimetre band, the propagation of the electromagnetic waves is severely affected by rain rate, dust particle size and drop size in the terms of attenuation, noise and depolarization. At the frequency above 10 GHz, the absorption and scattering by rain cause a reduction in the transmitted signal amplitude which will lead to the reducing of the availability, reliability and performance on the communications link. In this study, the rain effect on radio signal has been investigated. Spectrum analyzer and weather stations were used to obtain the RFI level and rain rate data respectively. The radio frequency interference (RFI) pattern due to rain factor was determined. This will benefit radio astronomer in managing sites for radio observation for radio astronomy purposes. (author)
[en] We present in this work a detailed design of a small low-pressure chamber outfitted with a ceramic porous plate for evaluating the soil water retention curve (SWRC) in the water potential range from 0 to -100 kPa. The chamber is made of acrylic and permits the use of one unique soil sample each time. The use of this chamber allows quick measurements of soil moisture using nuclear (based on gamma-ray attenuation) and conventional methods and SWRC determinations made with the designed chamber are in agreement with those obtained using a commercial low pressure chamber. The chamber was designed especially for testing the use of the nuclear method as an auxiliary tool for SWRC determinations but it can be easily adapted for routine investigations and a practical alternative for the conventional SWRC method. (authors)
[en] Radiation travelling through a medium could be attenuated in different ways depending on the type of medium. The research was done on the above basis and was carried out at the Medical Physics department of the National Hospital Abuja using the linear accelerator and an ionization chamber (farmer-type) which served as a radiation detector. The materials used for this research were: the Perspex, concrete, moulded clay (mud), wood, jean material, ordinary material (clothe), cardboard paper, ordinary paper and foam of which each was of (12 x 12 x 1)cm3 except for Perspex which was of (30 x 30 x 1)cm3. They were all beamed at one after the other using energy of 6MV photons from the linear accelerator. The chamber detected the radiation passing through each material and sent it (radiation) in minute current signals to an electrometer which read the signals in milligray. The results obtained indicated that Perspex would best attenuate radiation, but considering its cost, concrete is considered cheaper and next to Perspex from the results and would play a better role.
[en] In this work, mechanical and neutron attenuation properties of thermoplastic natural rubber (TPNR) blends filled with boron carbide (B4C) have been studied as a function of filler loading. Thermoplastic natural rubber of high density polyethylene/natural rubber (HDPE/NR) blends with different amounts of boron carbide (0-20 wt%) have been prepared via melt mixing method. All samples were subjected to tensile and neutron transmission test. The results showed that tensile strength and elongation at break of the composites were found to decrease with increasing filler loading. On the other hand, neutron shielding performance of the composites were found to improve significantly with the addition of B4C into TPNR matrix. (author)
[en] Attenuation studies on pure elements are straightforward and extensive data sets are available in the literature. However, studies on alloys are meagre due to the nonavailability of alloys of known composition in suitable form. Such studies are useful in estimating effective atomic numbers and to verify the validity of the mixture rule. Empirical expressions for these have been reported in the literature but several discrepancies have been noted. In the present study, transmission experiments were conducted in a narrow beam geometry for the photon energy range 60-400 keV, evaluating the effective atomic numbers for W/Cu alloy of two compositions, 65/35 and 60/40
[en] This study examined the change in the attenuation of X-rays with the ROI (Region of Interest) in DR (Digital Radiography) according to the stomach contents by manufacturing a tissue equivalent material phantom to simulate real stomach tissue based on the assumption that there is some attenuation of X-rays and a difference in imaging quality according to the stomach contents. The transit dosage by the attenuation of X-rays decreased with increasing protein thickness, which altered the average ROI values in the film and DR images. A comparison of the change in average ROI values of the film and DR image showed that the image in film caused larger density changes with varying thickness of protein than the image by DR. The results indicate that NPO (nothing by mouth) is more important in film system than in DR system.