Aluminum Hard Mask Technique for the Fabrication of High-Quality Submicron Nb/Al-AlOx/Nb Josephson Junctions

We have developed a combined photolithography and electron-beam lithography fabrication process for sub-\mum to \mum-size Nb/Al-AlOx/Nb Josephson junctions. In order to define the junction size and protect its top electrode during anodic oxidation, we developed and used the new concept of an aluminum hard mask. Josephson junctions of sizes down to 0.5 \mum2 have been fabricated and thoroughly characterized. We found that they have a very high quality, which is witnessed by the IV curves with quality parameters Vm > 50 mV and Vgap = 2.8 mV at 4.2 K, as well as IcRN products of 1.75-1.93 mV obtained at lower temperatures. In order to test the usability of our fabrication process for superconducting quantum bits, we have also designed, fabricated and experimentally investigated phase qubits made of these junctions. We found a relaxation time of T1 = 26 ns and a dephasing time of T2 = 21 ns

A Consistent Radionuclide Vector after the Chernobyl Accident.

The radionuclide vector in the release plume from the destroyed unit 4 of the Chernobyl Nuclear Power Plant was assessed. Emphasis was laid on radionuclides relevant for the internal dose, including those with short half-lives, and on the radionuclide vector in the 30-km zone where practically no data in air or foodstuff are available. An evaluation of data was performed by comparing core analysis data and actual measurements of air filters and deposition data. The derived nuclide vector is consistent with most measurements and core analysis data. The ratios of the various radionuclides with regard to the guide isotope 137Cs vary both with direction of release and with increasing distance from the power plant. The variation and its causes are discussed, and a credible, consistent model for the vector at arbitrary distances from the nuclear power plant, in particular with regard to non-volatile radionuclides, is given. In that way the observed large discrepancies of the radionuclide vector determined by Russian and Ukrainian researchers, and those measured in Central and Northern European are explained by the fact that 90Sr, 95Zr, 140Ba, and 144Ce, which showed a much higher ratio to 137Cs close to the reactor than at 1,000 km distance, were attached to particle sizes of 8 µm and thus quicker deposited than the volatile radionuclides which were attached to 1 µm particulates on average. Also, the 131I to 137Cs ratio changes with distance by almost one order of magnitude which is explained by the higher deposition velocity of iodine

First International Intercomparison of Luminescence Techniques Using Samples from the Teche River Valley.

Bricks collected from a contaminated village (Muslyumovo) of the lower Techa river valley, Southern Urals, Russia, were measured using thermoluminescence and optically stimulated luminescence by four European laboratories and a U.S. laboratory to establish and compare the applied dose reconstruction methodologies. The bricks, collected from 60-100-year-old buildings, had accumulated a relatively high dose due to natural sources of radiation in the brick and from the surrounding environment. This work represents the results of a first international intercomparison of luminescence measurements for bricks from the Southern Urals. The luminescence measurements of absorbed dose in bricks collected from the most shielded locations of the same buildings were used to determine the background dose due to natural sources of radiation and to validate the age of the bricks. The absorbed dose in different bricks measured by four laboratories using thermoluminescence and optically stimulated luminescence at a depth of 10 +/- 2.5 mm from the exposed brick surface agreed within +/-21%. After subtraction of the natural background dose, the absorbed dose in brick due to contaminated river sediments and banks was calculated and found to range between 150 and 200 mGy. The cumulative doses in brick due to man-made sources of radiation at 100 and 130 mm depths in the bricks were also measured and found to be consistent with depth dose profiles calculated by Monte Carlo simulations of photon transport for possible source distributions