The tunneling conductance of junctions formed on thin films of Al in contact~ith films of the ferromagnetic semiconductor EuO implies that such composites behave like BCS superconductors with internal magnetization.

A computationally efficient multinomial approximation of the count statistics that is based on the mean output spectrum can accurately predict imaging performance. This enables photon counting system designers to directly relate the effect of pileup to its impact on imaging statistics and how to best take advantage of the benefits of energy discriminating photon counting detectors, such as material separation with spectral imaging.

Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries.

Magnetically aligned samples of sintered YBa&Cu307 z were used to test the effects of oxygendeficiency 5 (with 5 0.2) on the superconductive magnetization M, critical current density J" irreversibility field B;",upper critical field H, t, coherence length g, condensation energy F"penetration depth A, , and related properties as a function of temperature T and applied field H~~c. In selected cases, studies were also made with H~~ab. The 0 content was monitored in situ by thermogravimetric analysis. The open porosity and granularity of the material allowed rapid and homogeneous oxygenation. We found no significant enhancement of intragrain J, with chain-site 0 defects. With few exceptions, maximum J, occurred at full oxygenation. This implies that chain-site 0 defects are not strong or effective pinning centers over most of the field-temperature regime investigated. Except for T"which was practically independent of 5 within the interval 0 & 5~0. 11 (so called "90-K T, plateau" ), most properties such as J" F"H,z, B;", (T), A, , and g were strongly and continuously influenced by the 0 deficiency. The observed abnormal magnetization with H~~c was weak at low T but became more pronounced as T and fi increased. No abnormal magnetization was detected with H~~ab. As oxygen was removed, B;"(T)and H,~(T) separated, and both lines shifted to lower T and lower B. Moreover, B;,"was strongly correlated with J, at low temperature. Determination of the thermodynamic critical field H, yielded condensation energies F,(5) that were well correlated with J,(5). The results indicate that 0 defects weaken the energy barrier of the existing pinning sites and have a negative overall effect on the capacity of YBazCu307 to carry loss-free currents.

We report the results of performance measurements for an amorphous silicon flat panel detector used in a cardiovascular imaging system. The detector contains 1024 x 1024 elements on a 0.2 mm pitch for an active image area of about 20.5 x 20.5 cm 2 . The system allows imaging at fluoroscopic and dynamic cardiac record exposure levels at rates of up to 30 Hz. We measured MTF, NPS, DQE, contrast ratio, response uniformity, resolution uniformity, and lag. Measurements were made on 28 production detectors. The MTF was greater than 0.2 at 2.5 cycles/mm. Contrast ratio was several hundred, indicating negligible long range scatter (veiling glare) within the detector. The DQE of the detector was measured at exposures typical of fluoroscopic imaging, dynamic cardiac record imaging, and digital subtraction angiography (DSA). The DQE was at least 0.65, 0.54, and 0.34 at 0, 1, and 2 cycles/mm, respectively, for all of these exposure levels. The response of the detector varied by less than 12% across its surface. The MTF, measured at nine positions over the surface of the detector, was found to have a maximum difference among positions of less than 0.05 at both 1 and 2 cycles/mm. First frame lag was less than 5%.

We have measured the critical magnetic 6elds H, 2t (parallel to a-b plane) and H, t& (perpendicular to a-b plane) of single crystals of YBa2Cu307 as a function of temperature in 6elds up to 19 T. The slope dH, -2fdT is greater by about a factor of 4 when the 6eld is applied parallel to the a-b plane than~hen it is applied parallel to the c axis.

Superconducting joints between Ag clad, Bi2Sr2Ca2Cu30z tapes have been obtained with approximately 1/2 the current capacity of the tapes themselves.

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