Vol.4,

The radiological environmental impact assessment of the nuclear industry in China has been completed. The effective dose equivalents to the critical groups are mainly within the fluctuation range of the average natural background radiation dose in the provinces, and below the dose limits. The annual average collective effective dose equivalent from the nuclear industry is approximately 23 man • Sv. According to the nuclear power planning of China, it is estimated that the annual collective effective dose equivalent from the nuclear fuel cycle and the application of radioisotopes is 59 man • Sv in 2000 a.

308

The nuclear dealignment is studied during the slowing down process and after thermolization in different gases by the time differential perturbed angular distribution method. A large fraction of the initial nuclear alignment following the nuclear reaction can be preserved in gases with large moments of inertia, but only a small fraction in monoatomic gases such as the noble gases. The plunger experiment shows that the nuclear dealignment occurs during the slowing down process and not after thermolization.

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282

The competing reactions between existing Ni silicides surrounded by Si and Ni were investigated by thermal annealing and MeV Si ion beam mixing. With high energy irradiation, the energy deposition at both interfaces, Ni/Ni silicide and Ni silicide/Si is equal. Two MeV He RBS and TEM were used to obtain the reacted layer composition and epitaxial orientation, respectively. Also glancing angle Co K_α X-ray diffraction was utilized to identify phase formation. The main results indicate that the existing silicides preferentially react with Ni layer, and that there are pronounced differences of Ni silicide phase transition between thermal annealing and MeV Si ion beam mixing, even though the mixing was performed in radiation enhanced diffusion regime. The results can be explained in term of the heat of silicide formation and surface energy change.

416

Evaluation of the Hubbell integral for an omnidirectional detector response to a rectangular plaque gamma emitting radiation source using a different numerical computation method on a personal computer was made. For a plaque consisting of several strip gamma emitters, exposure rates at different positions above the source were calculated using 'exact' evaluation and an approximate method. Optimization method is used to find source activity of each strip, so as to acquire desirable dose uniformity of the irradiated products. In uses of the Hubbell integral, by introducing appropriate programming, computation time can be saved.

286

EPA-standardized activated charcoal canisters were used to collect radon exhaled from building surfaces and analyzed using γ-spectroscopy to obtain the radon exhalation rates. More than 120 samples were analyzed in more than 10 buildings situated in different areas of Hong Kong. Variations were identified in the exhalation rates at different levels in a building, for different covering materials and for the presence of cracks in walls. The radon exhalation rate from the most common concrete walls and covering materials was found to be approximately 13 mBq • m^-2 • s^-1. This may be the cause of a relatively high indoor radon concentration in Hong Kong.

282

The interfacial structure of hard and soft oxides grown by dry oxidation on <100> n-type silicon substrates is examined using high resolution mild X-ray photoelectron spectroscopy (XPS) before and after irradiation. Substantial differences in silicon of silica state (B.E. 103.4 eV), silicon of transitional state (B.E. 101.5 eV), surplus oxygen (B.E. 529.6 eV) and negative two-valence oxygen (B.E. 531.4 eV) are observed between the two kinds of samples. The XPS spectra strongly depend on the conditions of irradiation for soft samples, but do not as remarkablely as soft samples for hard samples. The effects of irradiation doses on XPS are greater than that of irradiation bias fields. Some viewpoints of irradiation induced hole electron pair are proposed to explain the results.

326

In order to explore whether radon anomaly could be considered the precursor of rock slide, the forming mechanism of the radon anomaly is qualitatively analysed according to the relationship between rock rupture and radon content. It is indicated that the rock microfracture may be one of the reasons leading to the radon anomaly before rock slide, suggesting that the CR-39 solid state nuclear track detector could be used to monitor the radon concentration in the region of the slide. The information may then be used to predict rock slide.

266

This paper summarizes the results of the coprecipitation of ultramicrogram uranium with Fe(OH)₃ from saturated NaCl solution and separation of uranium from Fe(Ⅲ) by solvent extraction with TBP as extractant. In the first step, the coprecipitation efficiency of uranium is more than 95%; in the second step, extraction percentage of uranium is more than 98%, and stripping efficiency of uranium is nearly 100% (twice stripping) and separation factor (separation of Fe(Ⅲ) from uranium) is more than 10³.

292