The application of the Fourier transformation method to the measured EXAFS (Extended X-ray Absorption Fine Structure) curve has made it possible to determine the local atomic arrangement around an absorbing atom in crystalline and amorphous materials. A review has been made on the principle, characteristics and difficulties of this new method. A few variational methods of measuring the EXAFS curves are also described. Interesting results so far published are mentioned on various materials, including superconductors, catalysers and biologically important protein molecules, in crystalline, amorphous, dissolved and adsorbed states. The results obtained by the polarized X-rays and the structural changes under high pressure are also described. Finally, the relation between this EXAFS method and the X-ray diffraction method is illustrated from the viewpoint of X-ray anomalous scattering.
A precision thermostatic air chamber is described in which the air and the inner walls are kept at the same temperature. The air chamber has a double-walled structure and a heat exchanger of which the temperature effectiveness is close to 100%. The air and water passed through the heat exchanger are respectively forced to flow into the air chamber and into the interspace of the double walls. The trial air chamber described here is of cubic form each side of which is 30cm, and the thickness of the double walls is 30mm. The distribution of air temperature in the chamber is measured by 27 resistance thermo-meters arranged in a space lattice. Results of measurement with a thermostatic air chamber tester show that the temperature difference between the air and the inner walls is almost zero. Data are presented on the temperature control and the dynamic characteristics of the air chamber are discussed.
The formation of a current layer of a Z discharge of Ar gas at low pressure was studied-It is known that a current layer is usually formed on the wall of the discharge tube and imploded to the tube axis with increasing magnetic pressure. But such a current layer is nott always formed on the wall of the discharge tube in a low pressure experiment. The structure of the current layer at the formative phase was observed by an image converter camera. The position and form of the current layer at the formative phase were affected by the pressure of the filling gas and the distribution of the electric field strength and also of the ionization coefficient. When the discharge tube is covered by the return circuit and the gas pressure and electric field strength are changed, the forms of the current layer at the formative phase could be classified into three types, namely, shell, columnar and conic type.
A thermoelectric resistance thermometer for distant measurement described here is a grafted thermometer composed of a thermocouple and a resistance thermometer. The grafting portion of the thermoelectric resistance thermometer is connected by triple copper leading wiers of equal resistance to the electric meter. A constant current determined by the characteristics of both the thermocouple and the resistance bulb flows through the circuit composed of the couple and resistance bulb, and the potential difference between two fixed points in the circuit is measured. It is proved theoreti-cally that the measured potential difference gives the temperature to be determined. Experiments are carried out for the thermoelectric resistance thermometer with triple copper wires of 5_??_30m. long. The results show that the outputs of the thermoelectric resis-tance thermometer are in good agreement with the outputs of the thermoelectric thermometer with the reference' temperature at 0°C, and are independent of the length of lead wires and graft temperature.
A radio frequency oscillation has not been observed in any conventional two-electrode vacuum tube containing a cathode surrounded by a cylindrical anode. Rf oscillation is, however, generated in a specially designed two-electrode vacuum tube in which the anode is a thin wire parallel to the cathode, and where the anode current is within the range limited by the space charge. The oscillation has a very stable, monochromatic frequency spectrum, which has not been reported so far. This paper shows the experimental characteristics of the rf oscillation, and a theoretical description to explain the mechanism of the oscillation is also given. The theoretical results agree qualitatively well with those of the experiment. It is concluded that the rf oscillation is caused by the oscillation of moving electrons in a space charge field which has a cylindrical well. of potential with the anode at the centre.
Photoluminescence measurement is known to be a powerful technique to evaluate silicon crystals. When one determines the impurity concentration quantitatively by measuring luminescence intensities, however, many cau-tions should be paid especially with regard to the kinetics of photo-excited carriers. Here, we show the effect of changing the excitation intensity and of the presence of lattice defects on silicon luminescences.