Vol.16,

Microscopes in vacuum ultraviolet and soft X-ray regions using a normal incidence type of Schwarzschild objective are reviewed. The objective consists of a concave mirror and a convex mirror coated with a high reflectance multilayer, having a large numerical aperture comparing with other objectives. The microscopes have been used to diagnose inertia-confinement-fusion plasmas, and to investigate small samples or microstructures of inorganic and organic materials by imaging them using laboratory light sources. Synchrotron radiation has been also used to obtain a microbeam for a photoelectron scanning microscope with a spatial resolution of 0.1 μm. The structure and performance of two laboratory microscopes developed at Tohoku University are demonstrated. One of them is a soft X-ray emission imaging microscope. An image of an artificial pattern made of W and SiO₂ on Si wafer by focusing Si L emission was presented. The other is an ultraviolet photoelectron scanning microscope using a He (helium) gas discharge lamp. The valence band spectra of a microcrystal of FeWO₄ were presented. Furthermore other applications such as demagnifying optics for lithography and optics to gather fluorescence for emission spectroscopy are introduced.

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After molecular structure of UF₆ is optimized, molecular vibrational frequencies are calculated by LDA and GGA approaches. Some thermodynamic parameters are calculated based on the principle of statistic mechanics. Various functionals such as PWC, VWN, VWNPB, PW91, BP, PBE, RPBE, BOP with various basis sets such as MIN, DN, DND and DNP are used. The small basis sets, MIN and DN, can arrive at self-consistency. DMol³ can save more CPU's time and resource than all electron calculations including Hartree-Fock and DFT with Gaussian code, so it should be introduced in some research, especially on compounds of lanthanide and actinide. However, comparing with the results from classical DFT, the new calculation may accompany a rather large error.

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Thin strain-relaxed Si_0.81Ge_0.19 films (95 nm) on the Ar⁺ ion implanted Si substrates with different energies (30 keV, 40 keV and 60 keV) at the same implanted dose (3×10¹⁵cm^-2) were grown by ultra high vacuum chemical vapor deposition (UHVCVD). Rutherford backscattering/ion channeling (RBS/C), Raman spectra as well as atomic force microscopy (AFM) were used to characterize these SiGe films. Investigations by RBS/C demonstrate that these thin Si_0.81Ge_0.19 films were epitaxially grown on the Ar⁺ ion implanted Si substrates, although there existed lots of crystal defects. The relaxation extent of Si_0.81Ge_0.19 films on the Ar⁺ implanted Si substrates is larger than that in the unimplanted case, which were verified by Raman spectra. Considering the relaxation extent of strain, surface roughness and crystal defects in these SiGe films, the thin relaxed SiGe film on the 30 keV Ar⁺ implanted Si substrate is optimal.

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Measurements of radiation dose to patients in spiral computed tomography (CT) were completed for various collimations, table speeds and pitch. A standard CT head dosimetry phantom and thermoluminescent dosimeters (TLD) were used for the measurement. The effect of collimation and pitch on radiation dose was studied. The results indicated that the radiation dose at the given tube current, voltage and rotation speed was inversely proportional to pitch. And the increasing times of dose were as decreasing times of pitch. This regular pattern was tenable for radiation dose at both central holes and peripheral holes of the phantom at pitch = 1, >1 and <1. The collimation had no impact on the radiation dose. The results also indicated that radiation dose at central holes was nearly equal to that at peripheral holes. There was no significant difference between them statistically. The study demonstrates that the pitch in spiral CT scans is the primary parameter and has significant impact on radiation dose.

505

The aim of this study was to assess the usefulness of a mixture design for spent resin immobilization in cement as well as to examine the cement-slag-ash system for spent resin solidification. Eighteen distinct combinations, consisting of Portland cement, blast furnace slag, fly ash, organic ion exchange resins and water, were selected by a mixture design computer procedure to compose representative experiment points. The measured properties of solidified forms resulting from the combinations included 28-day compressive strength, 42-day immersion strength, 42-day immersion weight and slump. These data were fit to a mathematic model with the aid of Scheffé quadratic polynomial, and the effects of each ingredient on the measured properties were identified through an analysis of the response trace plots and contour plots. Utilization of an optimality function singled out an optimal combination comprising water=0.16(wt/wt), slag=0.21, ash=0.10, cement=0.27 and resin=0.26 from which the resulting response was 11MPa for the 28-day strength, 110mm for the slump and 5.4% for the 42-day increase in strength.

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In this paper we develop a general exact fan-beam reconstruction algorithm for free-form trajectories not only closed but also unclosed, based on the fan-beam reconstruction formula recently developed by Noo et al.. A mathematical proof is then provided with the geometrical explanation of equi-spatial detectors. With this algorithm we can obtain exact region of interest (ROI) reconstruction if and only if every projecting line passing through the ROI intersects the free-form source trajectory, when the projections are not truncated. Furthermore, under the condition that the source-to-detectors distance changes slowly enough relative to the length itself, we obtain a very good approximate reconstruction algorithm, which is the same as the algorithm of the circular trajectory except that the source-to-detectors distance is a function of the rotation angle. Then the algorithms are tested using the Shepp-Logan phantom and the experiment shows that the algorithms can get perfect numerical results.

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A nuclear power plant real-time engineering simulator was developed based on general-purpose thermal-hydraulic system simulation code RELAP5. It mainly consists of three parts: improved thermal-hydraulic system simulation code RELAP5, control and protection system and human-machine interface. A normal transient of CHASHMA nuclear power plant turbine step load change from 100% to 90% of full power, was simulated by the engineering simulator as an application example. This paper presents structure and main features of the engineering simulator, and application results are shown and discussed.

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During 1991-1993, the activity levels of the bone-coal mines were investigated in Zhejiang, Hubei, Hunan, Jiangxi and Anhui Province, respectively, where the reserve of bone-coal is about 90% of our country's total reserve. The average of γ radiation doserate level measured for bone-coal, bone-coal cinder (BCC) and bone-coal cinder brick (BCCB) in these provinces is about 500 nGy/h, 400 nGy/h and 700 nGy/h respectively, while that for fields, roads and houses made of BCCB in corresponding regions of these provinces is about 200 nGy/h, 260 nGy/h and 300 nGy/h respectively. It is shown that the environmental activity level of bone-coal mining area is about 3 times higher than the reference spots.

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It was investigated that the radon concentrations in bone-coal mining areas, in outside and inside BCCB houses and ordinary red-brick (ORB) houses of the reference points in Hubei, Hunan, Jiangxi, Zhejiang and Anhui Provinces. It was shown that the average annual radon concentration inside BCCB houses in the bone-coal mining areas in the five provinces ranges from 85.7 to 303 Bq/m³, with an average of 151 Bq/m³, which is 3 times that inside ORB houses at the reference points. The average annual radon concentration outside BCCB houses in the bone-coal mining areas in the five provinces ranges from 12.0 to 73.8 Bq/m³, with an average of 34.9 Bq/m³, which is 1.5 times that outside ordinary ORB at the reference points. And the radon concentration in shafts of Hubei and Zhejiang Province is 9.51×10³ Bq/m³ and 965 Bq/m³, respectively. This report also shows the changing patterns of radon concentrations with day, season, height, etc.

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