A superconducting X-ray spectrometer with a tantalum absorber andlateral trapping

We report the development of Nb-Ta-Al-Al₂O₃-Al superconducting tunnel junction structures for high energy resolution and high efficiency X-ray detection. These devices utilize a Ta X-ray absorber with superconductor “bandgap engineered” quasiparticle trapping to improve charge collection. Experimental results at 0.3 K are presented, showing energy resolution of 102 eV full-width-half-maximum for 6 keV X-rays. Collected charge is in excess of 5×10⁶ electrons. The absorption efficiency is better than 35%. Devices thermally cycle with no change in characteristics     

Optical properties of Zitex in the infrared to submillimeter

The results of measurements of the refractive index and power attenuation coefficient of Zitex at 290, 77, and 4 K in the spectral region from 1 to 1000 microm are presented. Zitex is a porous Teflon sheet with a filling factor of approximately 50% and is manufactured in several varieties as a filter paper. Zitex is found to be an effective IR block, with thin (200-microm) sheets transmitting less than 1% in the 1-50-microm range while attenuating < or = 10% at wavelengths longer than 200 microm. Some variation in the cutoff wavelength is seen, tending to be a shorter-wavelength cutoff for a smaller pore size. In addition, the thermal conductivity of Zitex at cryogenic temperatures has been measured and is found to be roughly one half that of bulk Teflon. Finally, its dielectric constant has been measured in the submillimeter as n = 1.20, resulting in extremely low dielectric reflection losses. As a result, Zitex is particularly useful as an IR blocking filter in low-noise heterodyne receivers; in the millimeter-wave range (lambda > or = 850 microm or nu < or = 350 GHz) the attenuation of alpha < or = 0.01 cm(-1) for a 3.5-mm thickness filter of Zitex G125 would raise receiver noise temperatures by <1 K.     

Superconducting Nb-Ta-Al-AlOx-Al tunnel junctions for x-ray detection

We report progress on the microlithographic fabrication of Nb-Ta-Al-AlOx-Al structures designed for x-ray detection. These structures use bandgap engineering both for quasiparticle trapping to increase the collection efficiency and to prevent quasiparticle diffusion out through the leads. Non-standard tunnel junction geometries are used to reduce the magnetic field needed to suppress the Josephson current for stable biasing. The performance of these devices as alpha particle detectors is presented.     

The effect of superplasticizer molecular weight on its adsorption on, and dispersion of, cement

The effect of molecular weight of a superplasticizer on the adsorption on cement was investigated by microelectrophoresis and UV-absorption techniques. The purpose of the experiments was to investigate any differences in the magnitude of the Zeta Potential (ZP) and in the amount of superplasticizer adsorbed by using sulfonated polystyrenes of different molecular weight, MW = 4,000 g/mole, MW = 16,000 g/mole, MW = 31,000 g/mole, and MW = 70,000 g/mole. The results show that the superplasticizer with the largest molecular weight gives the largest negative ZP, and would therefore be assumed to have a higher dispersing capability. UV-absorption results have shown that the polymer of MW = 16,000 g/mole is the most adsorbed of the four superplasticizers, whereas the polymers of MW = 4,000 g/mole, MW = 31,000 g/mole, and MW = 70,000 g/mole are less adsorbed, with MW = 70,000 g/mole being the least adsorbed. That the polymer which is the least adsorbed gives the highest negative ZP is explained by the diffuse double-layer theory.