Vol.17,

585

Molecular dynamics simulations have been used to study two topics of water molecules on hydrophobic surfaces. Some properties of the nanobubbles with different ingredients and behavior of single water chains in single-walled carbon nanochannels are exploited. Molecular simulations show that the density of the N₂ and H₂ are quite high, which is critical for the stability of the nanobubbles and may have potential applications, such as hydrogen storage, incorporated with recent experimental method to controllably produce hydrogen nanobubbles. The water molecules inside the nanochannel show an unexpected directed motion with long time period, which is indispensable in the future study of the dynamics of biological channels.

558

Ti-containing amorphous carbon (Ti-aC) coatings were deposited on cemented carbide and Si substrates by cathode-arc-enhanced closed field middle-frequency unbalanced magnetron sputtering. The coatings were studied by using atomic force microscopy, Raman scattering, nanoindentation, and pin-on-disk testing. The measurements showed that the hardness of the coatings increased from 12 GPa at a Ti content of 1 at.% to 27 GPa at 31 at.%. The coatings exhibited different friction behaviors when facing different mating materials and changed with increasing Ti content. The coating with 4 at.% Ti exhibited excellent tribological performance with a low friction coefficient of 0.07 when facing the cemented carbide.

431

A kind of alfalfa seeds was irradiated by 1, 2, 3, 4 and 5kGy at a dose rate of 6.288kGy·h¹ in a self-shielded irradiator of ¹³⁷Cs gamma rays. The EPR spectra, which were measured subsequently between 0.3401 and 0.3501T, showed that there was a direct proportional relationship between the EPR signal strength of free radicals produced by gamma irradiation in the alfalfa seeds and absorbed dose. The first derivative EPR spectra of the alfalfa seeds were very clear and easy to identify. However, the EPR signal strength of the peak-to-peak amplitude decreased rapidly and most of them decayed beyond 50% within 3 days after the seeds were irradiated. It tended to stabilize after half a month since the seeds were irradiated. The differences of the EPR signal strength between the irradiated and unirradiated alfalfa seeds still remained. All seeds were stored at ambient temperature for more than 3 months. Therefore, using EPR spectrometry technique to measure free radicals in alfalfa seeds as a means to determine whether the seeds have been irradiated or not is feasible, relatively fast and simple.

483

In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ-ray system have been described. The dual-energy γ-ray device is composed of radioactive isotopes of ²⁴¹Am and ¹³⁷Cs with γ-ray energies of 59.5 and 662 keV, respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The modified arithmetic is beneficial to removing the extra Compton scattering from the measured value. The result shows that the dual-energy γ-ray technique can be used in three-phase flow with average accuracy greater than 95%, which enables us to determine phase fractions almost independent of the flow regime. Improvement has been achieved on measurement accuracy of phase fractions.

651

Under laboratory conditions (i.e. a sealed system in which the temperature may vary according to air temperature), the migration of radon in upward, downward and horizontal directions has been investigated. After a period of accumulation, the spatial distribution profile of radon was drawn on the basis of the experimental data. The profile showed whorl-shape with bigger ends. The longer the accumulation time, the bigger the whorl end, and the higher the radon concentration is. By fitting the experimental data by least-square statistical method, we find that the distributions of radon follow negative exponential functions in the upward, downward and horizontal directions. However, exponents for the three directions are not exactly identical. The upward migration is more effective than the downward one and both upward and downward migrations are more effective than the horizontal one.

578

438

A kind of excellent CdZnTe crystal has been grown in Yinnel Tech, Inc. in recent years. Based on these CdZnTe crystals and some new techniques, a portable energy-dispersive spectrometer has been constructed which has yielded good results. CdZnTe detector has a 3% relative resolution in high-energy field and can detect gamma rays at room temperature. An integrated circuit based on preamplifier and shaping amplifier chips is connected to the detector. Voltage pulses are transformed into digital signals in MCA (multichannel analyzer) and are then transmitted to computer via USB bus. Data process algorithms are improved in this spectrometer. Fast Fourier transform (FFT) and numerical differentiation (ND) are used in energy peak's searching program. Sampling-based correction technique is used in X-ray energy calibration. Modified Gaussian-Newton algorithm is a classical method to solve nonlinear curve fitting problems, and it is used to compute absolute intensity of each detected characteristic line.

526

In this article we introduce an exact backprojection filtered (BPF) type reconstruction algorithm for cone-beam scans based on Zou and Pan's work. The algorithm can reconstruct images using only the projection data passing through the parallel PI-line segments in reduced scans. Computer simulations and practical experiments are carried out to evaluate this algorithm. The BPF algorithm has a higher computational efficiency than the famous FDK algorithm. The BPF algorithm is evaluated using the practical CT projection data on a 450 keV X-ray CT system with a flat-panel detector (FPD). From the practical experiments, we get the spatial resolution of this CT system. The algorithm could achieve the spatial resolution of 2.4 lp/mm and satisfies the practical applications in industrial CT inspection.

663

Different samples of igneous and metamorphic rocks from Egypt and Germany have been considered to measure γ-ray activity concentrations due to naturally occurring, potentially hazardous radonuclides ²²⁶Ra, ²³²Th and ⁴⁰K. The radiation hazard parameters including radiation equivalent activity, gamma-absorbed dose rate, and external and internal hazard indices have been estimated. The gamma-absorbed dose rates in air of rocks in Egypt range from 4.2 to 128.5 nGy·h^-1 with a mean value of 55.3nGy·h^-1. For igneous and metamorphic rocks from Germany, the values of absorbed dose rates fluctuate from 5.1 to 148.6nGy·h^-1, with a mean value of 60.9nGy·h^-1. Generally, it is found that the radiation hazard indices in common igneous rocks are distinctly higher in acidic than in ultrabasic rocks. The results are discussed and compared with the corresponding published data.

523

The aim of this study was to measure concentrations and distributions of natural radionuclides occurring in rocks. The activity concentrations (Bq·kg^-1) of the naturally occurring radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K in sedimentary rock samples from Eastern Desert (Um El-Huetat), Nile Valley (Gebel Owina) and from southwest Sinai (Wadi Ghweiba) were measured using a high-purity germanium detector. The samples under investigation (clay, shale and sandstone) were used as raw materials in the construction industry (bricks, ceramics, cement, fillers, etc.). Though the sediments of Egypt have already been investigated in the geological and mineralogical aspects, it is necessary to investigate the natural radioactivity in order to complete their classification. The average concentration values of ²²⁶Ra, ²³²Th, ⁴⁰K in the surveyed samples were 47 ± 7 , 21± 5, 393±19 Bq.kg^-1 (clay); 23 ± 5, 30 ± 6, 563 ± 24 Bq.kg^-1 (shale); and 17 ± 4, 14 ± 4, 299 ± 17 Bq.kg^-1 (sandstone), respectively. All sediment samples have radium equivalent activities ranging from 55 to 115 Bq·kg^-1, lower than the limit set in the OECD Report (370 Bq·kg^-1). The overall mean outdoor terrestrial gamma dose rates fluctuate from 28 to 55 nGy·h^-1. The external gamma radiation dose due to natural radionuclides present in the samples have been computed and compared with the global averages. In terms of the radiation safety, the natural radioactivity of the sediment in Egypt is below the recommended limits of the gamma dose rate. Therefore, they can be used for all kinds of public buildings.

481