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Notes: Abstract We discuss the short-and long-term perspectives of the CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) project and present the current status of the experiment and new results concerning detector development. In the search for elementary particle dark matter, CRESST is presently the most advanced deep underground, low-background, cryogenic facility. The basic technique involved is to search for WIMPs (Weakly Interacting Massive Particles) by the measurement of nonthermal 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. This will allow a test of the reported positive evidence for a WIMP signal by the DAMA Collaboration in the near future. In the long term, the present CRESST setup permits the installation of a detector mass up to 100 kg. In contrast to other projects, CRESST technology allows the employment of a large variety of detection materials. This offers a powerful tool in establishing a WIMP signal and in investigating WIMP properties in the event of a positive signal.

Notes: Abstract A mechanical decrepitation device coupled with a gas chromatograph has been used to characterize the molecular composition of gaseous and liquid hydrocarbons contained in minerals. Application of this technique allows the identification of low-molecular-weight n-alkanes and some aromatic hydrocarbons in sulfides and gangue minerals from epigenetic Variscan and post-Variscan lead–zinc deposits in the Rhenish Massif, Germany. Based on the analysis of 200 samples, Variscan and post-Variscan mineralization can be distinguished by the composition of associated hydrocarbons. Variscan sulfides and gangue minerals contain high abundancies of methane. In contrast, n-alkanes in the C2–C9 range and aromatic hydrocarbons (benzene, toluene) are dominant in post-Variscan mineralization. The absence of high-molecular-weight hydrocarbons in ore minerals suggests highly mature gas associated with hydrothermal activity, during which hydrothermal fluids caused an increase in thermal maturation of organic matter and the generation of low-molecular-weight hydrocarbons in the adjacent organic-rich rocks. The hydrocarbon compositions contained in fluid inclusions of Variscan and post-Variscan minerals are probably governed by the maturation level of the potential source rocks. In Variscan time tectonic brines (T 〉 175 °C) generated predominantly methane, whereas basement brines (T 〈 175 °C) expelled higher-molecular-weight hydrocarbons (wet gases, condensates, aromatic hydrocarbons) from adjacent rocks during the Mesozoic event. The specific role of hydrocarbons in sulfide precipitation via thermochemical sulfate reduction is indicated by geochemical characteristics of organic matter associated with the Plombières Pb–Zn deposit, in eastern Belgium. Intense alteration phenomena were observed in near-ore kerogens, compared with unaltered kerogens far from the ore body, as well as by a very high maturity (5.40% Ro), a systematic depletion in 12C towards the vein-type mineralization, high atomic S/C ratios (0.49), and by low atomic H/C ratios (0.29). The data suggest that hydrothermal solutions caused a drastic increase in the thermal maturation of organic matter within the adjacent wall rock. Increased thermal maturation resulted in increased δ13C-values of organic carbon due to the preferential release of 12C. The change in the organic matter to a H-depleted and S-enriched bulk composition in association with sulfide ores strongly suggests that thermochemical sulfate reduction was responsible for organic degradation. Thus, thermochemical sulfate reduction probably triggered base metal sulfide precipitation in Variscan and post-Variscan ore deposits of the Rhenish Massif. Finally, based on data from this study and previous investigations, new genetic models are presented for both Variscan and post-Variscan mineralization in the Rhenish Massif.

Notes: Many experiments in nuclear and particle physics would benefit from a device capable of detecting nonionizing events with a low energy threshold. We report on experimental tests of a low-temperature detector based on the registration of nonequilibrium phonons. The device is composed of a silicon single crystal with superconducting tunnel junctions (Al/Al2O3/Al) evaporated onto its surface. In first experiments a 20×10×3 mm3 crystal at an operating temperature of T = 0.37 K was tested with 5.5-MeV α particles. Pulse-height analysis and the timing of pulses in different junctions is shown to yield position and energy resolution. An energy threshold of 250 keV was estimated for absorption anywhere in the crystal. A position resolution of 0.6 mm was determined over a sensitive length of 10 mm. Though phonon focusing effects were registered in the vicinity of the [001] direction, scattered and reflected phonons dominate the signals in the general case. The experimental results are discussed in terms of ballistic and quasidiffuse phonon propagation. To improve the energy threshold, the operating temperature was lowered to 60 mK in order to increase junction sensitivity and a weak thermal coupling of the absorber to the heat bath was introduced to force phonons to leave the crystal via the detecting junctions. Si crystals of up to 20×20×10 mm3 size were used in these second experiments. With a 4 cm3 crystal a threshold of 270 keV was obtained. The performance in these experiments at 60 mK, however, was limited by exceptionally high values of the normal conducting junction resistances. With a reasonable value of this parameter it should be possible to realize an energy threshold of 1 keV with absorbers of a volume of several cm3.

Notes: An energy resolution of ΔE=12 eV [full width at half maximum (FWHM)] has been measured for the 55Mn Kα1 line (E=5.9 keV) using a superconducting lead absorber (90×90×1.3 μm3) readout by a single aluminum superconducting tunnel junction (100×100 μm2). The total detector area has been illuminated, while a slit mask of 150 μm width was used to partially shadow the detector leads and substrate area from impinging x rays. The total electronic noise contribution was measured as ΔEelec=4 eV (FWHM). The superconducting tunnel junction is located on a Si3N4 membrane of thickness 0.3 μm, the lead absorber is separated from the superconducting tunnel junction's top layer by a thin layer of natural aluminum oxide. No deviations from linear energy response were observed in the energy range between E=1.74 keV and E=6.49 keV. The same resolution was obtained for a single aluminum superconducting tunnel junction, where the influence of substrate events was suppressed by a metallic buffer layer between tunnel junction and substrate. The escape of recombination phonons into the substrate causes small nonlinearities in the tunnel junction's energy response. © 2001 American Institute of Physics.

Notes: Normal conductor-insulator-superconductor (NIS) junctions promise to be interesting for x-ray and phonon sensing applications, in particular due to the expected self-cooling of the N electrode by the tunneling current. Such cooling would enable the operation of the active element of the sensor below the cryostat temperature and at a correspondingly higher sensitivity. It would also allow the use of NIS junctions as microcoolers. At present, this cooling has not been realized in large area junctions (suitable for a number of detector applications). In this article, we discuss a detailed modeling of the heat flow in such junctions; we show how the heat flow into the normal electrode by quasiparticle back-tunneling and phonon absorption from quasiparticle pair recombination can overcompensate the cooling power. This provides a microscopic explanation of the self-heating effects we observe in our large area NIS junctions. The model suggests a number of possible solutions. © 1998 American Institute of Physics.