Hideaki Ido

Relation between Structural and Magnetic Properties of Compound MnAs1-xPx (0≦x≦0.275)

The crystallographic parameters of compounds MnAs 1- x P x (0≦ x ≦0.275) are determined as a function of temperature between about 100 and 600 K. It is found that these crystals except for MnAs take a MnP type structure in low temperature side and transform to a NiAs type at critical temperatures. These structural transitions are of second kind and accompanied with very large dilation (∼10%) of crystal volume. In order to see the relationship between the structural and magnetic properties, the temperature variation of magnetic susceptibilities of the compounds is also measured. Simple analysis of the experimental results, based on the Curie-Weiss law, reveals the way in which the spin value of Mn atoms and the exchange interaction between them depend on the crystal voluem (or lattice parameter).

Demonstration of enhanced K-edge angiography using a cerium target x-ray generator

The cerium target x-ray generator is useful in order to perform enhanced K-edge angiography using a cone beam because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. The x-ray generator consists of a main controller, a unit with a Cockcroft-Walton circuit and a fixed anode x-ray tube, and a personal computer. The tube is a glass-enclosed diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current were 65 kV and 0.4 mA, respectively, and the focal-spot sizes were 1.0 x 1.3 mm. Cerium Kalpha lines were left using a barium sulfate filter, and the x-ray intensity was 0.48 microC/kg at 1.0 m from the source with a tube voltage of 60 kV, a current of 0.40 mA, and an exposure time of 1.0 s. Angiography was performed with a computed radiography system using iodine-based microspheres. In coronary angiography of nonliving animals, we observed fine blood vessels of approximately 100 microm with high contrasts.

Quasi-monochromatic flash x-ray generator utilizing weakly ionized linear copper plasma

In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense characteristic x rays are produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The K lines were quite sharp and intense, and hardly any bremsstrahlung rays were detected at all. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity had a value of approximately 30 μC/kg at 1.0 m ...

Enhanced K-edge Angiography Utilizing Tantalum Plasma X-ray Generator in Conjunction with Gadolinium-Based Contrast Media

The tantalum plasma flash X-ray generator is useful for performing high-speed enhanced K-edge angiography using cone beams because K-series characteristic X-rays from the tantalum target are absorbed effectively by gadolinium-based contrast media. In the flash X-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash X-rays are produced by the discharging. The X-ray tube is a demountable cold-cathode diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic X-ray intensities of cerium increased. The K lines were clean and intense, and hardly any bremsstrahlung rays were detected. The X-ray pulse widths were approximately 100 ns, and the time-integrated X-ray intensity had a value of approximately 300 µGy at 1.0 m from the X-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography (CR) system and gadolinium-based contrast media. In the angiography of nonliving animals, we observed fine blood vessels of approximately 100 µm with high contrasts.

Variations in Cerium X-ray Spectra and Enhanced K-Edge Angiography

A cerium-target X-ray tube is useful in performing cone-beam K-edge angiography because K-series characteristic X-rays from the cerium target are absorbed effectively by iodine-based contrast media. The X-ray generator consists of a main controller and a unit with a high-voltage circuit and a fixed anode X-ray tube. The tube is a 1.0-mm-focus diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current were 65 kV and 0.4 mA, respectively. Cerium Kα rays were selected out using a barium sulfate filter, and the X-ray intensities without filtering and with a barium sulfate filter were 209 and 16.8 µGy/s, respectively, at 1.0 m from the source with a tube voltage of 60 kV and a current of 0.40 mA. Angiography was performed with an X-ray film using the filter and iodine-based microspheres 15 µm in diameter. In the angiography of nonliving animals, we observed fine blood vessels approximately 100 µm in diameter with high contrasts.

Effect of Pressure on the Curie Temperature of CrTe and MnSb Compounds of the Nickel Arsenide Type

The effect of the pressure on the Curie temperature of CrTe and MnSb compounds of the nickel arsenide were studied up to a pressure of 4,000 kg/cm 2 . The rate of change of the Curie temperature was -5.5×10 -3 °C kg -1 cm 2 for CrTe and (-3.2±0.5)×10 -3 °C kg -1 cm 2 for MnSb. From the result of the present experiment, the critical pressure and temperature to realize a first kind transition from a ferromagnetic to a paramagnetic state in CrTe are evaluated to be 41,000 kg/cm 2 and 107°K, respectively.

Magnetic Transition of the Mn2Sb-Mn2As System

The system Mn 2 Sb (1- x ) As ( x ) (0≦ x ≦1) is found to be solid solutions of the Cu 2 Sb type by X-ray analysis. A magnetic phase diagram has been produced by magnetic measurments in the temperature range 80 to 1100 K. Transition from antiferromagnetic to ferrimagnetic states with increasing temperature was observed for the compounds with x ≦0.4 and the compounds with x ≧0.55 were antiferromagnetic at all temperatures below the Neel temperatures. It is shown that these magnetic transition are explained qualitatively by the molecular field theory.

Compact monochromatic flash x-ray generator utilizing a disk-cathode molybdenum tube

The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -50 to -70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbo molecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean molybdenum Kalpha lines are produced using a 20 microm-thick zirconium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of -70 kV, the instantaneous tube voltage and current were 120 kV and 1.0 kA, respectively. The x-ray pulse widths were approximately 70 ns, and the generator produced instantaneous number of Kalpha photons was approximately 3 x 10(7) photons/cm2 per pulse at 0.5 m from the source of 3.0 mm in diameter.

Quasi-Monochromatic Flash X-Ray Generator Utilizing Disk-Cathode Molybdenum Tube

High-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -40 to -60 kV using a power supply, and the electric charges in the condensers are discharged to an X-ray tube after closing the gap switches in the surge generator using a trigger device. The X-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Sharp K-series characteristic X-rays of molybdenum are produced without using a monochromatic filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. The peak tube voltage increased with increasing charging voltage and increasing space between the target and cathode electrodes. At a charging voltage of -60 kV and a target-cathode space of 1.0 mm, the peak tube voltage and current were 110 kV and 0.75 kA, respectively. The pulse width ranged from 40 to 100 ns, and the maximum dimension of the X-ray source was 3.0 mm in diameter. The number of generator-produced K photons was approximately 7×1014 photons/cm2s at 0.5 m from the source.

Magnetic and Crystallographic Studies of Compound MnAs0.9P0.1

Crystallographic and magnetic properties of the compound MnAs 0.9 P 0.1 are studied in the temperature range from 4.2 to 660°K. X-ray diffraction studies reveal this compound deforms at 440°K with decreasing temperature from hexagonal B8 1 into orthorhombic B31 structure, as pointed out by Goodenough et al. . Degree of the orthorhombic deformation δ (shown in the text) in this case is first found to increase gradually from 440°K with lowering temperature, then rises steeply, reaching a δ-value of 2%, and remains constant with further fall of temperature. The magnetic measurements at low temperature reveal that the present compound is metamagnetic with saturation magnetization of 69 e.m.u. / g at 4.2°K, while it shows a ferromagnetic behavior above Liquid air temperature. Based on the present result, it can be shown that the manganese ion in this compound below Curie temperature is in a low spin state with spin value S =0.8. It is also shown that the manganese ions is in a high spin state for vanishing δ, ...