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Abstract. We present the current status of CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) project and new results concerning detector development. The basic technique involved is to search for WIMPs by the measurement of non-thermal phonons, as created by WIMP-induced nuclear recoils. Combined with our newly developed method for the simultaneous measurement of scintillation light, strong background discrimination is possible, resulting in a substantial increase in WIMP detection sensitivity. CRESST and the Dark Matter ProblemAfter a long period of development, cryogenic detectors are now coming on line and deliver significant results in particle-astrophysics and weak interactions. The goal of the CRESST project is the direct detection of elementary particle dark matter and the elucidation of its nature. Particle physics provides a well motivated dark matter candidate through the lightest supersymmetric (SUSY) particle, the 'neutralino' and one can find candidates in a wide mass range [1]. Generically, such particles are called WIMPS (Weakly Interacting Massive Particles). WIMPS are expected to interact with ordinary matter by elastic scattering on nuclei. Conventional methods for direct detection rely on the ionization or scintillation caused by the recoiling nucleus. This leads to limitations connected with the relatively high energy involved in producing electron-hole pairs. Cryogenic detectors use the much lower energy excitations, such as phonons. Since the principal physical effect of a WIMP nuclear recoil is the generation of phonons, cryogenic calorimeters are well suited for WIMP detection. Further, when this technology is combined with charge or light detection the resulting background suppression leads to a powerful technique to search for the rare nuclear recoils.The detectors developed by the CRESST collaboration consist of a dielectric target-crystal with a small superconducting film evaporated onto the surface. When this film is held at a temperature in the middle of its superconducting to normal conducting phase transition, it functions as a highly sensitive thermometer. The detectors presently employed in Gran Sasso use tungsten (W) films and sapphire (Al 2 O 3 ) absorbers, running near 15 mK. The technique can 2 J. Jochum CRESST collabroation also be applied to a variety of other materials. The small change in temperature of the superconducting film resulting from an energy deposit in the target leads to a relatively large change in the film's resistance. This change in resistance is measured with a SQUID. A small separate detector of the same type is used to see the light emitted when the target is a scintillating crystal. Present Status of CRESSTThe task set for the first stage of CRESST was to show the operation of four 262 g sapphire detectors, with a threshold of 500 eV under low background conditions. Meeting this goal involved the setting up of a low background, large volume, cryogenic installation and the development of massive, low background detectors with low ...

Linear sp-hybridized carbon chains have recently been proposed as one-dimensional nanostructures for electronic applications and as intermediate products in many nanoscale processes. However, their synthesis and observation are affected by their degradation upon oxygen exposure. Carbon chains consisting of alternating single and triple bonds (polyynic) are reported to be more stable than those consisting of double bonds (cumulenic), but the details of the degradation mechanism are still unknown. We use density functional theory to show that adsorption of O 2 on carbon chains anchored to carbon substrates can cause their cleavage through the collective scission of OÀO and CÀC bonds, yielding separate CO-terminated chains. Further O 2 attack progressively shortens them, causing CO 2 formation. While the shortening process has general validity, the cleavage step of the reaction is exothermic for cumulenic chains only. Perturbations of the ideal structure, such as bending of the chains or modifications to the structure of their termination, affect the oxidation mechanism and can make the cleavage reaction exothermic for polyynic chains as well. These results contribute to the interpretation of the available experimental results and reveal atomic-scale details of the oxidation process, thus allowing predictions on the chemistry of nanostructured carbon surfaces and suggesting possible new directions for the study of the chemical stability of carbynoid structures.

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