| 1. |
- Bovin, JO, et al.
(författare)
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Imaging of atomic clouds outside the surfaces of gold crystals by electron microscopy
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 47-49
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Tidskriftsartikel (refereegranskat)abstract
- The structure of small metal crystals has been intensively examined by high-resolution electron microscopy (HREM). In particular, multiply-twinned gold and silver crystals have been characterized using the profile-imaging method1,2 at atomic resolution, and reconstructed metal surfaces observed2. Crystal structure images of large gold clusters consisting of 55 gold atoms arranged in a cubeoctahedron have been recorded3 using 2.5 Å resolution, and crystal growth, row by row, on a {111} surface has been documented4 using a low-light-level silicon-intensified target television (TV) camera and video system with an on-line image processor. Direct imaging of rearrangements of atomic columns on extended gold surface5 established that profile imaging can provide information about surface self-diffusion. The motion of surface atoms, recorded with a real-time video tape-recorder (VTR) system, and the formation of surface atom steps on {100} surfaces, although not {111}, has also been reported recently6. Dynamic HREM observations at TV rate showing defect motion in gold7 and CdTe (refs. 8, 9) has given information on ‘in-lattice’ rearrangements of columns of atoms. We report here surface profile images recorded with the electron beam along the 〈110〉 direction with spatial resolution of ∼2.0 Å which reveal changes in occupancy of the atom columns often within periods of less than 0.1 s. Surfaces with several adjacent atom columns involved in rapid structural changes frequently interacted with a cloud of atoms extending out to 9 Å off the crystal and changes in shape and density of the clouds were recorded. Although these clouds have already been described6,10, the present work is the first to analyse these events properly and to describe them in detail. The motion of atomic columns and the existence of atom clouds revealed here may have important consequences for crystal growth, surface science and catalysis studies.
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| 2. |
- Coron, N., et al.
(författare)
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A Composite Bolometer as a Charged-Particle Spectrometer
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 314:6006, s. 75-76
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of radioactivity by direct conversion of nuclear radiation into a temperature rise of a calorimeter is as old as nuclear physics itself. As part of a general programme aiming at a determination of the mass of the electron neutrino, we have designed an improved version of a He-cooled composite diamond bolometer with a monolithic germanium thermistor, developed at the Laboratoire de Physique Stellaire et Planetaire (LPSP)1. Our approach, based on an idea by De Rujula2, is to study the shape, near the upper end-point of the internal bremsstrahlung spectrum in electron-capture β decay. The best nucleus for a precise measurement seems to be 163Ho, for which we have determined3 the Q EC value to be 2.83±0.05 keV. A particularly interesting possibility is to use total absorption spectrometry4 (calorimetry), in which the radioactive holmium forms part of the sensitive volume of the detector. With 5–6-MeV α particles impinging on the diamond wafer of the bolometer, a full-width-at-half-maximum (FWHM) of 36 keV was obtained at a temperature of 1.3 K. The theoretical resolution at 100 mK is a few electron-volts, so this new detection technique should give greatly enhanced energy resolution compared with present solid-state conductors based on charge carrier collection.
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| 3. |
- Larsson, Per
(författare)
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Contaminated sediments of lakes and oceans act as sources of chlorinated hydrocarbons for release to water and atmosphere
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 347-349
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric transport is a major route for entry of chlorinated, aromatic hydrocarbons into aquatic ecosystems. Once in the water, the compounds are readily taken up by the biota and distributed in the food webs. Major fractions of the compounds are deposited in the sediment1, and it had been thought that most persistent contaminants are inactivated in this way as a consequence of their lipophilic properties. However, results from recent laboratory studies2,3 raise the possibility that aquatic sediments may not be the final sink for the substances but may rather act as a source through redistribution of the compounds to water and the atmosphere. Polychlorinated biphenyls (PCBs) may be regarded as 'tracers' for these contaminants in the ecosystem, and I studied the transport of PCBs from sediment to water and air in two artificial ponds in the field. The transport from the sediment followed a seasonal cycle; higher concentrations of PCBs in water and air were recorded in the summer and lower in the winter. PCB concentrations in the air over the ponds were positively correlated with PCB levels in the water. My results show that contaminated sediments may act as a source of chlorinated hydrocarbons released into the environment.
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| 4. |
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