Library

Notes: Ni–Fe/FeMn bilayers were deposited by using dual ion beam sputtering apparatus. In order to promote (111) orientation in γ-FeMn layers and to exhibit exchange bias field Hex, Si and/or silicon nitride (Si3N4) layers were deposited as buffer layers. Although silicon nitride (Si3N4) buffer layers did not improve (111) orientation in FeMn layers, as well as in Ni–Fe layers, an amorphous Si buffer layer only 1 nm thick improved (111) orientation in FeMn layers and increased Hex to above 100 Oe. FeMn/Ni–Fe bilayers deposited on Si(0.5 nm)/Si3N4(1 nm) bilayered buffer layer also exhibited high Hex of about 130 Oe. This result implies that the ultrathin a-Si buffer layer was effective in improving (111) orientation in Ni–Fe layers. Very thin Si/Si3N4 bilayers may be applicable as dielectric layers in tunneling magnetoresistive spin valve devices. © 1999 American Institute of Physics.

Notes: A fluorescent x-ray source for medical imaging, such as K-edge subtraction angiography and monochromatic x-ray CT, has been developed. Using a 6.5 GeV accumulation ring in Tsukuba, fluorescent x rays, which range from about 30 to 70 keV are generated by irradiating several target materials. Measurements have been made of output intensities and energy spectra for different target angles and extraction angles. The intensities of fluorescent x rays at a 30 mA beam current are on the order of 1–3×106 photons/mm2/s at 30 cm from the local spot where the incident beam is collimated to 1 mm2. A phantom which contains three different contrast media (iodine, barium, gadolinium) was used for the K-edge energy subtraction, and element selective CT images were obtained. © 1995 American Institute of Physics.

Notes: Analogous to the localization of the wave function of an electron in a random potential (Anderson localization), in the macroscopic system of magnetoelastic waves (MEWs) propagating in a highly magnetostrictive string exhibiting the giant ΔE effect, the piling-up of MEWs into a wave-packet in a restricted small region of the string is expected. This wave-packet is subject to hopping in a discontinuous wave by applying a magnetic field due to the change in the local elastic states caused by the ΔE effect. From this expectation, a theoretical analysis was performed focusing on the derivation of localization conditions of MEWs. The analysis was carried out using a one-dimensional string model having high magnetostriction. The string is assumed to be composed of random chains with (1) alloy-type disorder (random weights of masses with equal spacings) and (2) liquid-type disorder (random spacings of masses with equal weights). For the elastic and magnetoelastic constants of the string, the value of Fe78Si10B12 amorphous wire (Unitika) were used in the calculations. No substantial changes in the localization states were not recognized in both modes. The analysis revealed that, when the change of the apparent Young's modulus with magnetic field ΔE is 28%, the localized MEWs are subject to hopping conserving their wave identities (eigenfrequencies and eigenstates). This result in considered to originate from the changes in the disorder conditions to support the localization of MEWs. To confirm the above theoretical prediction experimentally, MEW properties have been measured by using Fe78Si10B12 amorphous wires connecting weights made of leads to form the random chain structure. The localized MEWs are, indeed, observed by detecting the local vibrations of the wires. Theoretical and experimental results will be presented in detail at the conference. © 1997 American Institute of Physics.

Notes: Formation of a straight helical magnetic field is attempted by using ferromagnetic material. A shaped ferromagnetic cylinder, which modifies an external uniform magnetic field, is demonstrated to realize an l=3 helical magnetic field that is suitable for plasma experiments. The measured values for the angle of rotational transform and shear length agree with the predictions within a factor of 2, which is calculated without taking account of the self-demagnetization. This indicates that a rough configuration of magnetic field can be obtained even if the self-demagnetization is not known accurately. It is also suggested that this method is widely applicable to the formation of other complicated configurations of magnetic field.

Notes: Ischemic heart disease is one of the most popular and lethal diseases for aged peoples in the world, and is usually diagnosed by transarterial selective coronary arteriography. However, it is rather invasive and somewhat dangerous, so that the selective coronary arteriography is not feasible for prospective screening of coronary occlusive heart disease. Conventional digital subtraction angiography (DSA) is widely known as a relatively noninvasive and useful technique is making a diagnosis of arterial occlusive disease, especially in making the diagnosis of ischemic heart disease. Conventional intravenous subtraction angiography by temporal subtraction, however, has several problems when applying to the moving objects. Digital subtraction method using high-speed switching above and below the K edge could be the ideal approach to this solution. We intend to make a synchrotron radiation digital K-edge subtraction angiography in the above policy, and to apply it to the human coronary ischemic disease on an outpatient basis. The principles and experimental systems have already been described in detail by our coworkers.Our prototype experimental system is situated at the AR (accumulation ring) for TRISTAN project of high energy physics. The available beam size is 70 mm by 120 mm. The electron energy of AR is 6.5 GeV and average beam current is approximately 10 mA. This paper will show the animal experiments of our K-edge subtraction system, and discuss some problems and technical difficulties. Three dogs, weighing approximately 15 kg, were examined to evaluate the ability of our prototype synchrotron radiation DSA unit, that we are now constructing. The dogs were anaesthetized with pentobarbital sodium, intravenously (30 mg/kg). Six french-sized (1.52 mm i.d.) pigtail catheter with multiple side holes were introduced via the right femoral vein into the right atrium by the cutdown technique under conventional x-ray fluoroscopic control. Respiration of the dogs was controlled by a mechanical ventilator. The respirations were held for several seconds when taking the images. Approximately 10 to 15 ml of 76% water soluble iodinated contrast medium (Urografin 76, Schering) was injected by an automatic electronic injector at the rate of approximately 10 ml/s. Three or four times injections were done so as not to exceed the normal renal excretion threshold.Intravenous drip infusion of saline (500 ml/2 h) was used to accelerate the washout of contrast medium via renal system. One hundred micrograms of nitroglycerin were administered, intravenously to dilate the coronary arteries, approximately 3 min prior to contrast injection. Sometimes we used 0.1 mg/kg of beta blockage agent (Propranorol) to decrease the heart rate. Subsequently, the heart rate of the dogs was decreased from approximately 200/s to 100/s. These techniques are commonly used in human examinations. Materials are positioned at left anterior oblique view. The sequential images are now detected above the iodine K edge by an image intensifier (RTP 9240F, Toshiba) and recorded at high signal-to-noise ratio analog video recording system (C1900, Hamamatsu Photonics, S/N 45 dB). Proximal coronary arteries are well visualized, however the distal portions are unsatisfactory, because of the overlapping of the contrast-filled dense heart chambers and pulmonary vessels. Bolus injection of contrast medium is also necessary, unless overlapping is inevitable, so are the same in conventional intravenous DSA. The energy above and below the K edge is now changed by tilting the angle of crystal, mechanically, so it has not sufficient speed to subtract the moving material. Real time A/D converter and frame buffering memories have not been available, until now. Even though there are many limitations in the hardware and many problems to overcome, our preliminary animal experiments allow us to have high expectations.

Notes: A normal-conducting accelerating ring (NAR) has been constructed with a Chasman–Green-type lattice. The NAR has two basic aims. One aim is to prove the feasibility of the novel accelerating and storage scheme, in which the NAR accelerates the injected 15-MeV electrons to the final energy of 800 MeV, and directly stores them. The other aim is to make the NAR a multipurpose ring. That is, it acts as a booster for the superconducting storage ring, and it supplies the synchrotron radiation with the critical wavelength, 20.2 A. To achieve a high beam current, particular considerations have been taken with injection, rf system, magnetic field tracking, and vacuum formation. The NAR has experienced acceleration and storage at the final energy, 800 MeV. The initial beam current is about 20 mA in the 800 MeV storage mode.

Notes: A superconducting electron storage ring fully dedicated to x-ray lithography has been developed. It has a racetrack shape, consisting of two superconducting bending magnets, other normal conducting multipole magnets, rf system, vacuum system, and beam monitoring systems. The storage ring circumference is 16.8 m. The critical wavelength (λc) is 17.3 A(ring). The beam size (σ) at every synchrotron radiation source point is less than 1 mm. This machine employs the energy-boost-in-the-ring scheme; electrons are injected at around 15 MeV and then accelerated to 600 MeV in the ring. The injector is a newly developed linear accelerator with an energy compression system. Higher-energy injection is also available.

Notes: The aim of this study is to visualize the coronary artery with the intravenus injection of contrast media. We propose a method of rapid and successive acquisition of two-dimensional images in a digital processing system which uses a pair of video cameras, a shutter operation, and a beam-splitting apparatus. A prototype of the high-speed acquisition system was constructed. The two-monochromatic video-camera method was very suitable for quick acquisition. Electro-optical shutters (PLZT) were found practical with respect to the dynamic range and response time. The field blanking method was essential for the data acquisition.