22 research outputs found
Electronic Transport through YBCO Grain Boundary Interfaces between 4.2 K and 300 K
The current-induced dissipation in YBCO grain boundary tunnel junctions has
been measured between 4.2 K and 300 K. It is found that the resistance of 45
degree (100)/(110) junctions decreases linearly by a factor of four when their
temperature is increased from 100 K to 300 K. At the superconducting transition
temperature Tc the grain boundary resistance of the normal state and of the
superconducting state extrapolate to the same value.Comment: 14 pages, 4 figure
Electrical characterization of YBCO single crystal surfaces oriented in any crystallographic direction
Although considerable studies have been carried out, the true nature of
high-Tc superconductors (HTCS) is still not clear. Pseudogap phase at high
temperature as well as possible time reversal symmetry breaking at low
temperature need further investigations. The need of carefully made samples
showing the intrinsic properties of superconductivity is essential to test new
theoretical developments. We present in this paper how to control
crystallographic orientation in the junction and a technique developed to
determined the quality of the interface barrier between a gold electrode and a
HTCS : YBCO. This potentially allows us to perform Andreev spectroscopy in the
CuO2 planes of cuprate superconductors as a function of temperature,
crystallographic orientation and doping.Comment: 13 pages, 5 figures, LaTeX, using elsart clas
Evaluation of the Neutron Data Standards
With the need for improving existing nuclear data evaluations, (e.g., ENDF/B-VIII.0 and JEFF-3.3 releases) the first step was to evaluate the standards for use in such a library. This new standards evaluation made use of improved experimental data and some developments in the methodology of analysis and evaluation. In addition to the work on the traditional standards, this work produced the extension of some energy ranges and includes new reactions that are called reference cross sections. Since the effort extends beyond the traditional standards, it is called the neutron data standards evaluation. This international effort has produced new evaluations of the following cross section standards: the H(n,n), 6Li(n,t), 10B(n,α), 10B(n,), natC(n,n), Au(n,γ), 235U(n,f) and 238U(n,f). Also in the evaluation process the 238U(n,γ) and 239Pu(n,f) cross sections that are not standards were evaluated. Evaluations were also obtained for data that are not traditional standards: the Maxwellian spectrum averaged cross section for the Au(n,γ) cross section at 30 keV; reference cross sections for prompt γ-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the 252Cf spontaneous fission neutron spectrum and the 235U prompt fission neutron spectrum induced by thermal incident neutrons; and the thermal neutron constants. The data and covariance matrices of the uncertainties were obtained directly from the evaluation procedure
A new evaluation of the neutron data standards
Evaluations are being done for the H(n,n), 6Li(n,t), 10B(n,αγ), 10B(n,α), C(n,n), Au(n,γ), 235U(n,f) and 238U(n,f) standard cross sections. Evaluations are also being done for data that are not traditional standards including: the Au(n,γ) cross section at energies below where it is considered a standard; reference cross sections for prompt gamma-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the 235U thermal neutron fission spectrum and the 252Cf spontaneous fission neutron spectrum and the thermal constants
Improvements and extensions of the neutron cross section and fluence standards
Improvements have been made to the nuclear data standards largely as a result of an IAEA Data Development Project. The work includes the traditional activities related to standards, extending the energy ranges of some standards, and reference data that are not as well known as the standards but can be very useful in the measurements of certain types of cross sections. Also included is an effort to improve evaluations of 235U thermal and 252Cf spontaneous fission neutron spectra