Vol.17,

It is demonstrated that two kinds of soft X-ray spectroscopy are useful as nondestructive methods to investigate multilayer structures modified by interdiffusion or by chemical reaction of adjoining layers in depth direction. One is the total electron yield (TEY) spectroscopy involving angular dependence measurement. Using this method, it was found that in LiF/Si/LiF trilayers, the Si layers exhibited a characteristic similar to porous Si, and in CaF₂/Si/CaF₂ trilayers, it was found that CaF₂ segregated through the Si layer. Moreover, it has been shown that the thickness of the top layer of a Mo/Si X-ray multilayer can be determined by analyzing TEY signals generated by the standing wave. The other is the soft X-ray emission spectroscopy involving spectral shape analysis. Using this method, it was found that in Mo/Si X-ray multilayers, the interdiffusion or chemical reaction giving rise to deterioration of reflectance character occurs in as-deposited samples as well as in heated samples. In antiferromagnetic Fe/Si multilayers, it was confirmed that there was no existence of pure Si layers, but insulating FeSi₂ layers were present. This result suggests that the source of antiferromagnetic coupling is not conduction electrons but quantum wave interference.

527

The aim of the present investigation is to determine initial G2-chromosome aberrations and to validate whether the G2-chromosome aberrations can predict the cellular clonogenic survival in human tumor cell lines. Cell lines of human ovary carcinoma cells (HO8910) and human hepatoma cells (HepG2) were irradiated with a range of doses and assessed both for initial G2-chromosome aberrations and for cell survival after γ-irradiation. The initial G2-chromosome aberrations were measured by counting the number of G2-chromatid breaks after irradiation, detected by the premature chromosome condensation technique, and the G2-assay method. Cell survival was documented by a colony formation assay. A linear-quadratic survival curve was observed in both cell lines. The dose–response results show that the numbers of G2-chromatid breaks increase with the increase in dose in the two cell lines. At higher doses (higher than 4Gy) of irradiation, the number of G2-chromatid breaks for the G2-assay method cannot be determined because too few cells reach mitosis, and hence their detection is difficult. A good correlation is found between the clonogenic survival and the radiation-induced initial G2-chromatid breaks per cell (r=0.9616). The present results suggest that the premature chromosome condensation technique may be useful for determining chromatid breaks in G2 cells, and the number of initial G2-chromatid breaks holds promise for predicting the radiosensitivity of tumor cells.

459

A study of the fragments of DNA irradiated with MeV ions is important for the understanding of the DNA damage mechanism and the subsequent biological effects (induced by heavy ions). In this experiment, the products of calf thymus DNA (CT DNA) irradiated with MeV fluorine ions were analyzed using agarose gel electrophoresis, modified time-of-flight mass spectrometer (MALDI-TOF), and high-performance liquid chromatography (HPLC). The results showed that the molecular mass of the fragments were concentrated around 831 bp with agarose gel electrophoresis, there was no observable product in the range of 1,000-30,000 (m/q) using MALDI-TOF, and small biomolecules were separated from the products. The results of this study indicated that the strand breaks of calf thymus DNA induced by MeV fluorine ions were nonrandom.

528

This article mainly presents the application of Geant4 package (Geant4.7.0, 2005), developed by CERN (the Center of European Research of Nucleus), in medical physics and a novel technique, namely, hadrontherapy. The distribution of energy deposition in a water model by different radiation beams was also given. The results show that the distributions for proton beams are completely different from those for other radiation beams. Charged particles like protons exhibit little scattering when they penetrate the matter and give the highest energy deposition near the end of their range just before they reach the resting state. These characteristics permit very precise control of the shape of the energy distribution inside the patient's body.

540

With the increasing use of fullerenes and their derivatives in a variety of fields, the toxicity and effects of fullerenes on humans and the environment have received considerable attention. In this study, the cytotoxicity of fullerene derivative, C₆₀(OH)x, on Tetrahymena pyriformis was investigated. Cell growth inhibition was evaluated by counting with an optical microscope, and the generation time was calculated. It was indicated that the fullerenols caused a dose-dependent growth inhibition of the cells. The morphologic change in the damaged macronucleus of cells was observed using a fluorescent microscope. Superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and glutathione reductase (GR) levels were also measured for Tetrahymena pyriformis, using conventional methods. The results showed that fullerenols could reduce GSH-PX and GR activities. But no noticeable difference in SOD activity was observed between the treated groups and the control group. This indicated that the antiproliferative effect of fullerenols might be mediated by the reduction in the activities of GSH-PX and GR of cells and the destruction of the macronucleus.

474

^99mTc-HMIBP, a new bone-imaging agent, was prepared by the reduction of ^99mTc-pertechnetate in the presence of SnCl₂•2H₂O. The effects of the amounts of SnCl₂•2H₂O and HMIBP and the pH value on the labeling yield and radiochemical purity of ^99mTc-HMIBP were investigated. When the amounts of SnCl₂•2H₂O and HMIBP were more than 10 µg and 2.5 mg, respectively, the pH value was between 2 and 7, and the labeling reaction continued for 10 min, both labeling yield and radiochemical purity of ^99mTc-HMIBP were more than 90%. The biodistribution in rats and bone scan in rabbits were also studied. The results showed that the bone uptake is up to 7.94% ID/g at 30 min after injection of ^99mTc-HMIBP, bone-to-muscle and bone-to-blood uptake ratios were 20.89 and 16.89, respectively. The clear bone image was obtained at 120 min after injection of ^99mTc-HMIBP and clearance in soft tissue was visible. All of the above-mentioned results suggested that ^99mTc-HMIBP may be a potential bone-imaging agent.

470

Among the various micro-pattern gas detectors (MPGD) that are available, the gas electron multiplier (GEM) detector is an attractive gas detector that has been used in particle physics experiments. However, the GEM detector usually needs thousands of preamplifier units for its large number of micro-pattern readout strips or pads, which leads to considerable difficulties and complexities for front end electronics (FEE). Nowadays, by making use of complementary metal-oxide semiconductor (CMOS)-based application specific integrated circuit (ASIC), it is feasible to integrate hundreds of preamplifier units and other signal process circuits in a small-sized chip, which can be bound to the readout strips or pads of a micro-pattern particle detector (MPPD). Therefore, CMOS ASIC may provide an ideal solution to the readout problem of MPPD. In this article, a triple GEM detector is constructed and one of its readout strips is connected to a CMOS charge-sensitive preamplifier chip. The chip was exposed to an ⁵⁵Fe source of 5.9 keV X-ray, and the amplitude spectrum of the chip was tested, and it was found that the energy resolution was approximately 27%, which indicates that the chip can be used in triple GEM detectors.

458

678

The natural radioactivities in three major groups of foodstuff widely consumed in Upper Egypt were determined. The specific activities of ²²⁶Ra, ²³²Th, and ⁴⁰K in cereals, leguminosae, and flour were measured using γ-ray spectroscopy. Another group of hay, water, and soil samples from the same location were also analyzed. Hay samples were found to contain the highest radioactivity concentration among all the samples that were investigated. This increment could be due to the high water content in the shoots which tends to accumulate soluble radionuclides. The average calculated concentrations of soil samples in the present study exhibits the lowest values with respect to those from different countries. In the case of water samples, the average activities of both ²³²Th and ⁴⁰K were similar to those for soil while ²²⁶Ra was twice that of water sample. The annual ingestion dose from each radionuclide was calculated. The computed annual dose owing to daily intake of radium, thorium, and potassium via wheat flour, lentils, and bean in the present study (214.8 µSv) is ten times lower than the global average annual radiation dose (2400 µSv) from the natural radiation sources as proposed by UNSCEAR. The obtained results show that the dose values are quite low and carry insignificant radiation dose to the public.

530

The technology of passive safety is the current trend among safety systems in nuclear power plant. Passive residual heat removal system (PRHRS), a major part of passive safety systems of Chinese advanced PWR, is a novel design with three-fold natural circulation. On the basis of reasonable physics and mathematics models, MITAP-PRHRS code was developed to analyze steady and transient characteristics of the PRHRS. The calculation and analysis show that the code simulates steady characteristics of the PRHRS very well, and it is able to simulate transient characteristics of all startup modes of the PRHRS. However, the quantitative description is poor during the initial stages of the transition process when water hammer occurs.

462

In this article, a core fuel management program for hexagonal pressurized water type WWER reactors (CFMHEX) has been developed, which is based on advanced three-dimensional nodal method and integrated with thermal hydraulic code to realize the coupling of neutronics and thermal-hydraulics. In CFMHEX, all these feedback effects such as burnup, power distribution, moderator density, and control rod insertion are considered. The verification and validation of the code system have been examined through the IAEA WWER-1000-type Kalinin NPP benchmark problem. The numerical results are in good agreement with measurements and are close to those of other international institutes.

593

This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single-phase conservative equations for the primary circuit and the steady-state two-phase drift-flux conservative equations for the secondary side of the steam generator, the natural circulation characteristics were studied. On the basis of the preliminary calculation analysis, it was found that natural circulation mass flow rate was proportional to the exponential function of the power and that the value of the exponent is related to the operating conditions of the secondary side of the steam generator. The higher the outlet pressure of the secondary side of the steam generator, the higher the primary natural circulation mass flow rate. The larger height difference between the core center and the steam generator center is favorable for the heat removal capacity of the natural circulation.

459