Electrical breakdown of Ge in the neighbourhood of liquid helium temperature is studied by d. c. sweep technique. With Sb-doped N-type Ge, a remarkable current rise in its otherwise monotonous V-I (voltagecurrent) characteristics is observed which is considered to be caused by impact ionization. Typical P-type Ge doped with In shows negative resistance at Ec a little above its critical field value. V-I characteristics of quenched Ge containing about 2×1016/cc Cu atoms shows the unusual steps, and with some specimens, transient negative resistance of S-form is observed. With Ga-doped and strongly Sb-compensated Ge, the amount of negative resistance that appears depends on the degree of compensation; with Ga-doped but uncompensated Ge, the negative resistance is found slowly varying which however disappears when observed by a. c. or pulse method instead of d. c. method. In the former case in a range of extremely low temperature of below 5°K, the sign of Hall coefficient changes from P-type to N-type, which seems to be of use as a key to elucidate the mechanism of impurity conduction.
Scratch on glass surface made by sliding of a steel edge is studied. Microscopic and phasemicroscopic observations are made before and after acid treatment. The scratch generally has two different parts. One is the destroyed part consisting of cracks that are cavities filled with air readily recognizable by the naked eye or under microscope. The other is the region where glass has been turned into an abnormal state by severe stress. Such a region can be recognized by phase-microscopy or by chemical “developing”. An explanation is proposed of the shape of the cracks, wich is based on qualitative analysis of the stress. It is inferred that some tensile strain is permanently left in the “abnormal” region.
The electrical resistance dew point hygrometer has the sensitive part of an electrical resistance hygrometer placed in a small case provided with two pipes. The gas to be measured is let in through one pipe and out through the other. If the relative humidity of the gas is too low to measure, the gas is cooled from outside of the case and if too high, the gas is heated. Dew point of a gas is not altered by changing the temperature if the pressure is made to remain constant.
Radiation effects on methyl silicone rubber and phenyl silicone rubber are studied by the use of gamma rays of cobalt-60. With increasing radiation dose, irradiated samples become harder eventually turning glass-like; Young's modulus, breaking stress and average stiffness are all enhanced; maximum degree of elongation and weight swelling ratio are reduced. The change in these values is smaller for phenyl silicone rubber than for methyl silicone rubber which is considered attributable to protective effect of phenyl radical against radiation-induced crosslinking. From Young's modulus and weight swelling ratio, number of crosslinks in pure silicone rubber was calculated, the number being found proportional to radiation dose. Different methods of calculating this number gave more or less different values even for the same sample, but when the same method was applied, phenyl silicone rubber was found to have a smaller number of crosslinks than methyl silicone rubber.
An experimental study has been made on the breakdown characteristics of alloyed germanium p+-n junctions. Breakdown characteristics are found to be controlled by the Zener effect when a specific resistivity of the n-type base is lower than 0.14 ohm cm (corresponding to the breakdown voltage of 19 V), whereas avalanche type breakdown is observed in case when the base resistivity is higher than that value. Between Zener and avalanche regions, distinct differences of such breakdown properties as temperature dependency of the breakdown voltage, current multiplication phenomena, generation of microplasma in low temperature and dependency of breakdown voltage on impurity concentration of the base crystal are observed. Samples used throughout these experiments are defectless alloyed junctions having sharp breakdown characteristic about which the author previously reported.
In biological and medical research, it is often necessary to keep a sample at constant temperature. Moreover, to know thermodynamic quantities of the sample such as entropy, activation energy, etc., a thermostatic bath which can be easily controlled in a wide range of temperature is highly desirable. A thermoelectric system is applied for this purpose. A water bath of 100 ml is quickly cooled and warmed between 0°C and 50°C with 4 couples of thermoelements. The thermoelectric power of a couple is α=360×10-6 V deg-1. Temperature is detected by a thermistor and read directly on a HYS type microammeter. With the aid of a small lamp and a phototransistor mounted on the scale of the ammeter, and a suitable amplifier-relay system, temperature is easily controlled within ±0.1°C. Theoretical analysis and experimental proof for these thermoelectric systems are described.
Thermoelectric cooling of photomultiplier for astronomical observation has been devised with the use of four pieces of thermoelectric panel, each panel consisting of fourty couples of thermo-element. Cold sides of these panels are in close contact with four sides of a square aluminum block with a cylindrical cavity in which a prepared photomultiplier is placed; hot sides of the panels are attached to panels cooled by circulating water. The photomultiplier and vital parts, a resistor for one, are sealed in an evacuated cylindrical aluminum case to keep their surface free from condensation of water vapor which would otherwise cause current leakage. The case has an optically flat fused quartz window which is kept warmed by a 100 W electric heater to prevent dew forming on its surface. These arrangements enable observations to be made in adverse weather. In trial with ambient temperature of 26°C, photomultiplier EMI 6262 was cooled down to about -10°C in about one hour whereby the dark current was reduced to 1/30_??_1/20 of the uncooled.
Internal friction in quenched iron-nickel alloys (5.031.6% Ni) containing a small amount of nitrogen or carbon was measured with a torsion pendulum and two peaks of internal friction were observed around 40°C and 160°210°C with a frequency of vibration of about 1.7 cycles per second. The 40°C peak is the same as the Snoek's peak associated with the stress-induced diffusion of nitrogen or carbon in α-iron. The more Fe-Fe interstitial sites in the iron-nickel alloys, the higher the peak of internal friction becomes. Thus it seems likely that the interstitial nitrogen atom is more stable at the Fe-Fe interstitial site than at the Ni-Ni or Fe-Ni site. It is supposed that the origin of the high temperature peak of internal friction in the quenched iron-nickel alloys is the same as that of an internal friction peak observed in cold-worked iron, for the values of activation energy associated with the peaks and the peak temperatures in both cases are nearly equal. Thus it seems probable that the main cause of the high temperature peak of internal friction in the iron-nickel alloys is an interaction between lattice defects produced by a martensitic transformation and interstitial solute atoms (nitrogen or carbon atoms).
Optical absorption coefficient of 7--ray irradiated PMMA and copolymers MMA-AN increases with dosage first linearly up to about 4 x 105r, then assumes transient saturation in about 6×106γ_??_1×107γ region, after which it resumes the increase slowly and parabolically reaching its final saturation. The region of initial linear increase can be used for measuring high doses of radiation. Copolymers MMA-AN in particular give rise to very strong absorption bands of small fading coeffi-cient in visible region and are therefore convenient materials for devising handy dosimeters. Irradiation induces in the copolymers two kinds of absorption simultaneously, one is due to conjugated double bonds, the other is due to color centers and/or trapped radicals. The former appears in ultraviolet region and is irreversible, while the latter is in visible region, partly vanish-ing suddenly by heating above glass transition temperature, partly producing conjugated double bonds by atom rearrangement. Below glass transition temperature, however, the color centers and/or the trapped radicals, the chromophores, are firmly captured by the lattices and do not recom-bine, therefore are stable, but in free air they are completely bleached by oxygen leaving a distinct mark of boundary below the surface of the plastics suggesting that the oxygen molecules adsorbed on the surface penetrate it according to the law of diffusion and react on the chromophores. Penetration rate depends on dosage, composition of the plastics and temperature.