Vol.5,

The contents of total and methyl mercury in scalp hair samples of 1179 fishermen living at a typical Hg-polluted region in Northeast China and 27 lying-in women and their new born babies in Beijing have been determined by instrumental neutron activation analysis, gas chromatography (electron coupling) and other techniques. Only 18 of all fishermen have the Hg contents above 5 µg/g, which indicates that the Hg pollution there has been substantially alleviated. The longitudinal Hg patterns of the lying-in women show a gradually lowering tendency during pregnant period. Further, the Hg contents of the new-born babies are generally above or close to those of their mothers, confirming the mechanism that the methyl Hg, an organic species of Hg with high toxicity, is readily able to penetrate the placental barrier and accumulated in fetus. Thus, the mercury poison has occurred at the early stage of pregnancy.

428

Experimental method to measure the prompt neutron spectra of ²³⁸U fission induced by fast neutrons has been developed at HI-13 Tandem Van de Graaff Accelerator Laboratory of CIAE. These techniques employ a multi-segment fission chamber and two liquid scintillator neutron detectors. TOF (time of flight) techniques are used for primary neutrons to select the fission events induced by monoenergetic neutron from ²H(d, n) reactions instead of breakup neutrons from ²H(d, np) reactions. The fission neutron TOF spectra are measured in coincidence with the fission fragments to distinguish fission neutrons from other secondary neutrons. The method permits measurements to a fairly good accuracy under large neutron and gamma ray background. The techniques are described and experimental spectra are presented.

372

281

In routine thermoluminescence (TL) dating, there is often a tendency to omit an absolute determination of the thorium and uranium content in the sample and simply measure the total alpha count rate. The annual dose is then calculated assuming equal activities for a Th/U weight ratio of about 3.17. In fact this ratio is varied significantly in pottery. Calculation of the annual dose conversion factors from data using the total alpha count rate in a selected range of Th/U weight ratios shows significant differences. The results indicate that the additional error contribution to the final TL age is in the range ±2.5% to ±4.1% for most cases where the Th/U ratio lies between 1.1 and 9.5.

325

A new kind of electron source, the photoemissive monoenergetic electron source has been invented for calibrating the beta-magnetic spectrometer. It produces electrons in the form of simulating a radioactive monoenergetic electron source and can be made in any shape and size according to the demands of experiments. In this paper, the principles and basic constructions of the photoemissive monoenergetic electron source are described, the results of calibrating our 2^1/2 π beta-magnetic spectrometer with a single strip arc shaped photoemissive monoenergetic electron source are listed, a new way for determining resolution function of experimental system in the research of neutrino rest mass has been posed and one of its actual applications is also given.

665

Accumulation of enriched ²³⁵U-UO₂F₂ in the body had injurious effects on the immune function of central and peripheral immune cells. After an intravenous injection of ²³⁵U-UO₂F₂, the spontaneous ³H-TdR incorporation in thymocytes and bone marrow cells decreased, with the thymocytes damaged more markedly. The proliferation ability of spleen T and B lymphocytes were both inhibited, with B lymphocytes inhibited more severely. In spleen B lymphocytes the IL-1 production and IL-2 consumption were diminished. The inhibition of spleen B lymphocyte proliferation by ²³⁵U-UO₂F₂ was partially restored by adding exogenous IL-1 or IL-2 to the cultured lymphocytes obtained from ²³⁵U injected mice.

498

A small unbalanced magnetron atom source with multipole cusp magnetic field anode is described. The co-axial magnetron principle is extended to the circular planar magnetron atom source, which raises the efficiency of sputtering target area up to 60 %. The multipole magnetic field is put in the anode, which makes the unbalanced magnetron atom source run in a higher discharge current at a lower arc voltage condition. Meanwhile, the sputtering atoms through out the anode can be ionized partially, because the electron reaching the anode have to suffer multiple collisions in order to advance across the multipole magnetic field lines in the anode, which enhances the chemical reactivity of the ejecting atoms in film growth and improve the property of film depositing.

377

The design of a small complex-type focussed magnetron with a long target-life used for excited multi-atoms beam film deposition in hard coatings is described. The magnetron tunnel of the magnetron source was constructed by a planar unbalanced magnetic annulus, which comes from the extended co-axial magnetron principle and inside cylindrical magnet tunnel. The use efficiency of inside circular cone sputtering target area is high up to 62%. The inside-inversion cone sputtering target has a long life and results in a higher deposition rate 35 nm/min for Ti at a 2.5 Pa Ar pressure. A better focussing direction of ejecting atom beam has been achieved, and the arc power input is 300W for Ti target.

474

The time interval of neibouring neutrons emitted from a steady state neutron source can be treated as that from a time-dependent neutron source. In the rock space, the neutron flux is given by the neutron diffusion equation and is composed of an infinite number of "modes". Each "mode" is composed of two die-away curves. The delay action has been discussed and used to measure the time interval with only one detector in the experiment. Nuclear reactions with the time distribution due to different types of radiations observed in the neutron well-logging methods are presented with a view to getting the rock nuclear parameters from the time interval technique.

489

A systematic investigation of γ radiation effects in gate SiO₂ as a function of the fluorine ion implantation conditions was performed. It has been found that the generation of interface states and oxide trapped charges in fluorinated MOSFETs depends strongly on implantation conditions. The action of F in oxides is the conjunction of positive and negative effects. A model by forming Si-F bonds to substitute the other strained bonds which easily become charge traps under irradiation and to relax the bond stress on Si / SiO₂ interface is used for experimental explanation.

304