Gold beads of equal sizes are sintered in a small cylindrical vessel under Compressive load. The relations among the diameter of bead, load, sintering time and the lowest sintering temperature (the temperature for the beginning of sintering) are determined by the method described in the former report1). The diameters of beads tested are 1.35, 0.85 and 0.45mm. For example, the beads (0.85 mm in dia.) are sintered at 413°K for 5 minutes under a load of 3.5kg or at 1203°K for 5 minutes under no load. These temperatures are 30 and 90% of the melting point of gold respectively. The value of ξ=(-dlog TS/dlog W)r, t=const changes with the lowest sintering temperature Ts, where ξ is the rate of lowering of the lowest sintering temperature with the increase of load under the same sintering time and radius of beads. In the case of 0.85 mm in diameter, the value of ξ has a maximum value at a little higher temperature than the range of the recrystallization temperature of gold (100°_??_400°C). The ratio of the diameter of the adhered area between two beads to the diameter of the bead is found to take a certain value, 7%, independent of the dimension of the bead under no load, but it becomes larger with the load. In the case of 0.85 mm in diameter, it is 7_??_10 between 0_??_100g in load and 10_??_54% between 100_??_3500 g in load. The activation energy for beginning of sintering between two beads is found to take a certain value regardless of the dimension of the bead, but it changes with the lowest sintering temperature. It becomes smaller with the sintering temperature, but has a minimum value within the range of recrystallization temperature and then it becomes larger. Its minimum value is about 18 kcal/mol and the largest value is 290 kcal/mol. These values are 1/3 and 6 times as large as the activation energy of self-diffusion of gold respectively.
The results of laboratory and field experiments on the propagation of ultrasonic pulses in concrete are reported. The data obtained are believed to be useful in measuring the dynamic elastic constants and Poisson's ratio of concrete structures of dams in particular. Langevin type vibrators of barium titanate ceramic, with the resonance frequency of 21 Kc/e are found most suited as the sending and the receiving units for the purpose. The main results of the fields tests are as follows: In concrete dams, it is possible to measure the compressional waves and the surface waves separately, so that the Poisson's ratio can be computed from the measured values. The transverse waves can be observed when the sending and the receiving units are in particular relative positions and angles. The propagation waves are accompanied by secondary waves of frequencies far lower than the natural frequency of the sender, and the propagation of the surface waves through long distances is found to depend chiefly on such secondary waves. This shows the importance of the secondary waves for which the data obtained by fundamental experiments are given in addition.
WO3 is monoclinic at a room temperature and has a domain structure with walls of (110) and (100) twin planes. (110) wall is displaced vertically by a unidirectional pressure externally applied along b-axis with the change of axis b to shorter axis a. (100) domains change to a single domain by stress Xz. Single domain crystal obtained by this method is used to determine the optic elasticity axes of WO3. Two peculiar types of domain structure appear by a pressure along c-axis, which can be understood as a result of the change of axes c _??_ a by the stress. The sensitivity of domain structure to the stress thus witnessed seems to be due to the pseudosymmetric structure of WO3 crystal.
Characteristics of ZnS(Ag) phosphor for a-particle detection are described. Investigations are made on some commercial ZnS (Ag) for (a) the preparation of phosphor screen, (b) the relation between photomultiplier voltage and counting ratio using screens of varying thicknesses, (c) the relation of thickness vs. counting efficiency, (d) the effect of thickness on pulse height distribution of Po-α particles and (e) the effect of activator Ag content. Also, (a) comparison with other phosphors, (b) application to T (d, n) He 14 MeV neutron monitor and (c) application of fast decay component to fast coincidence, are tried. It is found that the grain size and screen thickness are important, as ZnS(Ag) phosphor is in powder form and is opaque to its own fluorescent light. Desirable result for a-particle detection is obtained with high backgrounds of γ-rays and neutrons.
A direct measurement method to study the distribution of a-particles in air near the ground surface has been deviced using nuclear plates. The instrument consists of some nuclear plate cameras, a suction pump and rubber tubes which are connected to each camera. The sample air is introduced into the camera through the rubber tube supported at a appropriate height. After some hours of suction the number of tracks of α-particles on the nuclear plate are counted. Results seem to show no agreement with the theoretical presumptions of recent investigators.
The possibility of roughness of surface being measured by means of jelly containing radio isotope is confirmed. The jelly is spread over the surface, scraped flat with a straight edge under predetermined conditions, dried and the count by radiation counter is taken, The count is proportional to what the author calls the mean 3-dimensional roughness determined by the amount of jelly that filled up and smoothened up the unevenness. The results are compared with the roughness measured with electrical capacitance method.
The extension of the image of a point source formed by any optical system is practically limited to some finite area in the image plane. As a consequence the sampling theorem can be applied to the plane of the exit pupil. The process is the counterpart of the sampling theorem applied to the image plane. The case of optical system with spherical aberration only is studied. It is shown mathematically that, if the Fourier spectrum G (R) of a two dimensional radial function g(r) contains no frequency higher than 1, then g(r) is expanded in the series of _??_ with the coefficient g(μs), where μs is the s-th root of the Bessel of _??_J, with the coefficient g(μs), where μs is the s-th root of the Bessel function of order zero, and the spectrum G (R) is completely determined by giving a discrete set of g (p). If we represent by G (R) the complex amplitude of the image in a limited area, g (r) corresponds to the pupil function, and the former can be expressed by a set of g (μs). As an example the intensity of the image is calculated for a lens with spherical wave aberration of 3/4 λ.