16 research outputs found
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The ATLAS Positron Experiment -- APEX
APEX -- the ATLAS Positron Experiment -- is designed to measure electrons and positrons emitted in heavy-ion collisions. Its scientific goal is to gain insight into the puzzling positron-line phenomena observed at the GSI Darmstadt. It is in operation at the ATLAS accelerator at Argonne National Lab. The assembly of the apparatus is finished and beginning 1993 the first positrons produced in heavy-ion collisions were observed. The first full scale experiment was carried out in December 1993, and the data are currently being analyzed. In this paper, the principles of operation are explained and a status report on the experiment is given
X-ray Diffraction Study on Cooling-Rate-Induced ÎłfccâΔhcp Martensitic Transformation in Cast-Homogenized Fe-26Mn-0.14C Austenitic Steel
The thermal stability of a cast homogenized austenitic steel with basic composition Fe-26Mn-0.14C has been studied using the Rietveld entire X-ray diffraction (XRD) pattern fitting technique. The decomposition of austenite was observed to be very sensitive to the cooling rate. A very high proportion (49 to 70 pct) of Δ-martensites was found in the differently cooled specimens as well in the as-cast specimen. The density of various planar (stacking and twin) faults was also estimated in both Δ-martensites and retained austenite. The significant variation in the extent of Îł fccâΔ hcp martensitic transformation was interpreted in terms of athermal and isothermal martensites formed during cooling and grain size of austenite. The austenite grains were found to be comprised of a high to moderate density of stacking faults (âŒ10â3 to 10â2) and negligible twin fault probability (âŒ10â5). On the other hand, in the Δ-martensites, the dominant planar fault was twins (âŒ10â3). Approximate values of the dislocation density within the retained austenite were also evaluated using the crystallite size and root-mean-square (rms) strain values obtained from the âsize-strain-shapeâ analyses