Conductive Cooling of SDD and SSD Front-End Chips for ALICE

We present analysis, technology developments and test results of the heat drain system of the SDD and SSD front-end electronics for the ALICE Inner Tracker System (ITS). Application of super thermoconductive carbon fibre thin plates provides a practical solution for the development of miniature motherboards for the FEE chips situated inside the sensitive ITS volume. Unidirectional carbon fibre motherboards of 160 -300 micron thickness ensure the mounting of the FEE chips and an efficient heat sink to the cooling arteries. Thermal conductivity up to 1.3 times better than copper is achieved while preserving a negligible multiple scattering contribution by the material (less than 0.15 percent of X/Xo)

Isotopic fingerprints of gold-containing luminescence centers in 28Si

We have recently shown that the dramatic reduction in linewidth of many deep luminescence centers in highly enriched 28Si can lead to the observation of isotopic fingerprints, revealing not only that a specific element is involved in the defect complex, but also the number of atoms of that element. This has led to many surprises regarding the actual constituents of supposedly well known luminescence centers, as well as the discovery of new members of a family of four-atom centers where the constituents can be chosen from Cu, Ag, Au and Li. Obtaining the isotopic fingerprint of Au is problematic, since only 197Au is stable, but we have now used the relatively long-lived 195Au to reveal the presence, and the number, of Au atoms in several of these centers. We find a series of four-atom centers containing one Au plus Cu and/or Li. Surprisingly, the Au isotopic fingerprint also reveals a series of five-atom centers containing a single Au plus Cu and/or Li. Further evidence for the ubiquity of these four- and five-atom defects is provided by two previously observed Pt-related centers, with luminescence at 884 and 777 meV, which are present in these samples due to the decay of 195Au to 195Pt. In addition to Pt, these centers are found to contain three and four Cu atoms, respectively

Isotopic fingerprints of Pt-containing luminescence centers in highly enriched Si-28

Recently we have shown that the reduction in the photoluminescence linewidth of many deep luminescence centers in highly enriched Si-28 results in well-resolved isotopic fingerprints. This allows for a better characterization of a defect center, as not only the involvement of a specific element but also the number of atoms of that element within the complex can be determined. Surprisingly, we have found that many well-known luminescence centers have a different composition than originally supposed. In addition, we have found a large number of four- and five-atom luminescence centers involving the elements Cu, Au, and Li. Here we introduce series of four- and five-atom deep luminescence centers involving a single Pt atom together with Cu and Li, similar to what has been seen previously for Au-containing luminescence centers

Large-scale Production of Highly Enriched 28Si for the Precise Determination of the Avogadro Constant

An attempt is described to replace the present definition of the kilogram with the mass of a certain number of silicon atoms. A prerequisite for this is that the Avogadro constant, NA, is determined with a relative uncertainty of better than 2 × 10−8. For the determination, silicon crystals are used. However, the difficulty arising thereby is the measurement of the average molar mass of natural Si. Consequently, a worldwide collaboration has been launched to produce approximately a 5 kg 28Si single crystal with an enrichment factor greater than 99.985% and of sufficient chemical purity so that it can be used to determine NA with the targeted relative measurement uncertainty mentioned above. In the following, the first successful tests of all technological steps will be reported (enrichment of SiF4, distillation into silane and chemical purification, chemical vapour deposition of polycrystalline 28Si, floating zone growth of a dislocation-free single crystal) and new equipment for the production of high-purity 28Si with an enrichment of not less than 99.99% will be described. All steps are well defined by a Technical Road Map (TRM28) and all key results are measured by new mass spectrometric, IR spectroscopic and other chemical and physical methods, such as Hall effect, photoluminescence, laser scattering and x-ray topographic methods (TRM for Analytical Monitoring and Certification, TRM28-AMC). The initial enrichment of the gas is >0.999 95 and the depletion during the entire process is <0.000 05. The isotopic homogeneity is checked by natural Si crystal growth and does, in the enriched sphere, not exceed 5 × 10−10, relatively. The C content of the final material is less than 1015 atoms cm−3 and the specific resistance is 400–1000 _ cmJRC.D.4-Isotope measurement