Ken’ichi Takahashi

Design of neutron detector by using a novel superconductor MgB2

Abstract It is difficult to detect neutrons compared to charged particles. A novel metallic superconductor MgB 2 has a high T c of 40 K. It is well known that the 10 B has a huge cross-section for the nuclear reaction of 10 B( n , α ) 7 Li. It reaches 3800 barns for thermal neutrons. The Li particle has 0.84 MeV while α particle has 1.47 MeV. We propose to use the MgB 2 as a superconducting neutron detector. We design a prototype of a MgB 2 neutron detector from an MgB 2 film where the electron beam lithography is employed to fabricate a meandering MgB 2 stripe line of the 1-μm width. The hot spot caused by the nuclear reaction is responsible for detecting neutrons.

Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB2

We examine the superconducting anisotropy γ c =(m c /m a b ) 1 / 2 of a metallic high-T c superconductor MgB 2 by measuring the magnetic torque of a single crystal. The anisotropy γ c does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter y c =4.31′0.14. The torque curve shows the sharp hysteresis peak when the field is applied parallel to the boron layers. This comes from the intrinsic pinning and is experimental evidence for the occurrence of superconductivity in the boron layers.

Electrical properties of bulk BSCCO/IN interfaces

Abstract The influence of Ag-doping and Ag sputtering on electrical properties of bulk BSCCO/In interfaces were examined. In Ag-doped and undoped samples, Rc were ∼ 10 −6 ω cm 2 and ∼ 10 −3 ω cm 2 , respectively. While Rc of Ag-doped samples showed positive dependency on magnetic field, there was no dependency in undoped samples. Ar ion beams ethcing, Ag sputtering with moderate film thickness and anneal treatments to an undoped sample significantly decreased Rc (∼ 10 −6 ω cm 2 ).

Preliminary study of oxide superconductors for wire fabrication

Abstract Super-GM is promoting R&D of manufacturing wires for oxide superconductor to apply to the power sector as the national project supported by AIST,MITI and NEDO. As the first step, solid method, liquid method and gas phase method for synthesizing various oxide superconductor were examined, and for the improvement of current density, it is required to make the materials more compact , more homogeneous and more enhanced in crystal orientation.

Evidence for superconductivity in the boron layers of MgB2

Abstract We examine the superconducting anisotropy γ= m c /m ab of a metallic high-Tc superconductor MgB2 by measuring the magnetic torque of a single crystal. The anisotropy γ does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter γ=4.31±0.14. The torque curve shows the sharp hysteresis peak when the field is applied parallel to the boron layers. We consider that this comes from the intrinsic pinning and is direct evidence for the occurrence of superconductivity in the boron layers. This is consistent with what the band calculations predict in the electronic states.

High transport critical current properties of oxide superconductors prepared by solid, liquid and vapor phase processes

Abstract The R&D of oxide superconductors by Super-GM has covered studies on synthesizing methods and the control of properties from the view points of achieving higher critical current density (Jc) and higher critical current (Ic), etc., for examination on wire formation, aiming at the application to power apparatuses. As a result, Jc values on the order of 10 6 A/cm 2 were obtained with thin films, and on the order of 10 4 A/cm 2 with bulk, and Ic values of more than 100 A were obtained with bulk, and on the order of 10 A (77K, 0T), even with films.

Influence of Contact Resistance on Ic Measurement of Bi Based Oxide Superconductor

In a measurement of critical current (critical current density) using 4-probe method, a number of factors, such as contact resistance, influence the measurement results according to Ic increasing. In this study, using Bi based superconductor prepared by FZ method, influences of temperature and magnetic field on electrode contact resistance and influence of pulsating current conditions on critical current measurement were studied. Using the 10−5Ω cm2 sample we obtained almost same Ic in the conditions of pulsating current in the range of 50~ 2000msec. On the other hand, samples with high contact resistivities were melt in the conditions of long pulsating current. Moreover we observed the microstructure with the immediate vicinity of contact by EPMA analysis.