J. Åström , P.C.F. Di Stefano, F. Pröbst, L. Stodolsky, J. Timonen, C. Bucci, S. Cooper, C. Cozzini, F. v. Feilitzsch, H. Kraus, J. Marchese, O. Meier, U. Nagel, Y. Ramachers, W. Seidel, M. Sisti, S. Uchaikin, L. Zerle 1 Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 Munich, Germany; 2 Technische Universität München, Physik Department, D-85747 Munich, Germany; 3 University of Oxford, Physics Department, Oxford OX1 3RH, UK; 4 Laboratori Nazionali del Gran Sasso, I-67010 Assergi, Italy; 5 Joint Institute for Nuclear Research, Dubna, 141980, Russia; 6 CSC IT Center for Science, P.O.Box 405, FIN-02101 Esbo, Finland; 7 Department of Physics, P.O. Box 35 (YFL), FIN-40014 University of Jyväskylä, Finland; 8 Institut de Physique Nucléaire de Lyon, Université Claude Bernard Lyon I, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex, France; 9 Institute of Chemical Physics and Biophysics, EE-0026 Tallinn, Estonia; University of Warwick, Dept. of Physics, Coventry CV4 7AL, UK, ∗ Corresponding author, email address: les@mppmu.mpg.de.

In the early stages of running of the CRESST dark matter search with sapphire crystals as detectors, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time that the energy release in fracture has been accurately measured on a microscopic event-by-event basis. The energy distributions appear to follow a power law, dN/dE proportional to E-beta, similar to the Gutenberg-Richter power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the autocorrelation function shows time correlations lasting for substantial parts of an hour. Some remarks are made concerning the possible role Of Such mechanical stress release processes in the noise of sensitive cryodetectors. (c) 2006 Elsevier B.V. All rights reserved.

In the early stages of running of the CRESST dark matter search using sapphire detectors at very low temperature, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time the energy release in fracture has been directly and accurately measured on a microscopic event-by-event basis. The energy threshold corresponds to the breaking of only a few hundred covalent bonds, a sensitivity some orders of magnitude greater than that of previous technique. We report some features of the data, including energy distributions, waiting time distributions, autocorrelations and the Hurst exponent. The energy distribution appear to follow a power law, dN/dE proportional to E-beta, similar to the power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the waiting time w or gap distribution between events has a power law behavior at small w and an exponential fall-off at large w, and can be fit proportional to w(-alpha)e(-w/w0). The autocorrelation function shows time correlations lasting for substantial parts of an hour. An asymmetry is found around large events, with higher count rates after, as opposed to before, the large event. (c) 2006 Elsevier B.V. All rights reserved.

We have developed massive cryogenic particle detectors to be used in the CRESST dark matter search. Each detector is made of a sapphire crystal and a tungsten superconducting phase transition thermometer. In this paper, we report on the results obtained with four 262g detectors, which show energy thresholds as low as 350eV and good energy resolution at low energies. The shape of the experimental pulses, the linearity of the detector response and the energy dependence of the resolution are discussed.

Diffusion of quasiparticles over distances up to 4 mm has been observed in various superconducting films. The quasiparticles were created by X-ray absorption in film strips with critical temperatures near 1 K and were detected in two superconducting phase transition thermometers at the ends of each strip. Position and energy of the absorbed X-rays as well as diffusion constants and lifetimes of the quasiparticles were determined. Very long lifetimes up to 9 ms allow the realization of large area phonon collector films on massive cryogenic particle detectors. Recently, with a first such detector a high efficiency of the phonon collection could be demonstrated.

A method to stabilize cryogenic detectors with superconducting phase transition thermometers in their operating point is presented. Measurements of X-ray lines emitted by an 55Fe X-ray fluorescence source showed an improvement in energy resolution from 230 to 133 eV on the 1.5 keV aluminium line with this technique. Furthermore the required set-up allows to simulate real events by injecting heat pulses into the thermometer and in this way to calibrate the detector and to monitor its long-term stability.

We report on simultaneous detection of phonons and scintillation light using a cryogenic calorimeter composed of a scintillating CaWO4 crystal and a separate light detector, both instrumented with a tungsten superconducting phase transition thermometer operating at about 12 mK. Clear discrimination between electron and nuclear recoils was demonstrated by irradiating the detector with electrons, photons and neutrons. The shape of the nuclear recoil energy spectrum induced by the neutrons could be well reproduced by simulations.

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation.

We have developed a detector, consisting of a cryogenic calorimeter with a scintillating crystal as an absorber, and a second calorimeter for the detection of scintillation light, both operated at 12 mK. Using a CaWO4 crystal with a mass of 6 g as the scintillating absorber, we have achieved a discrimination between nuclear recoils and electron recoils with a suppression factor of 99.7% at energies above 15 keV. This method will be applied for background rejection in the CRESST dark matter search (Cryogenic Rare Event Search with Superconducting Thermometers).

For the first time, the 41Ca signal from the nuclear weapon tests has been measured. Calcium 41 concentrations have been determined in alpine ice of the Fiescherhorn glacier (Switzerland) with accelerator mass spectrometry. The peak concentrations have been observed to be about 3 x 106 atoms of 41Ca per kilogram of ice in the 1950s. It has been found that 41Ca is produced essentially by the atoll bombs. A universal box model, able to describe atmospheric transport of radionuclides that are in gaseous form or attached to aerosols, has been developed. The model has been applied to calculate the bomb pulses of 14C; 36C1; 41Ca; øøSr, and 137Cs. For the transport of radionuclides that are attached to aerosols such as 41Ca, 9øSr, and 137Cs, sedimentation (gravitational settling) in the upper stratosphere has been taken into account. It has been found that the deposition of bomb-produced 36C1 on the Earth's surface is delayed compared to that of øøSr by about 1 year because 36C1 stays gaseous in the stratosphere. The model can also be used to calculate the deposition of cosmogenic radionuclides, e.g.,36C1 and 1øBe, in

For the first time, the 41Ca signal from the nuclear weapon tests has been measured. Calcium 41 concentrations have been determined in alpine ice of the Fiescherhorn glacier (Switzerland) with accelerator mass spectrometry. The peak concentrations have been observed to be about 3×106 atoms of 41Ca per kilogram of ice in. the 1950s. It has been found that 41Ca is produced essentially by the atoll bombs. A universal box model, able to describe atmospheric transport of radionuclides that are in gaseous form or attached to aerosols, has been developed. The model has been applied to calculate the bomb pulses of 14C, 36Cl, 41Ca, 90Sr, and 137Cs, For the transport of radionuclides that are attached to aerosols such as 41Ca, 90Sr, and 137Cs, sedimentation (gravitational settling) in the upper stratosphere has been taken into account. It has been found that the deposition of bomb‐produced 36Cl on the Earth's surface is delayed compared to that of 90Sr by about 1 year because 36Cl stays gaseous in the stratosphere. The model can also be used to calculate the deposition of cosmogenic radionuclides, e.g., 36Cl and 10Be, in their natural archives, such as polar ice sheets.

We are preparing the CRESST experiment to search for dark matter WIMPs using cryogenic detectors with superconducting phase transition thermometers. In the first stage we plan to use four 250 g sapphire detectors with thresholds of 0.5 keV and resolutions of 0.2 keV at 1 keV. This will provide sensitivity to WIMP masses below 10 GeV, and is thus complementary to other dark matter searches.

Spallation cross sections for the reaction 40Ar(p, 2p3n)36Cl are measured in the energy range 47–1000 MeV. The results are used to calculate the production of cosmogenic 36Cl on atmospheric argon by solar protons and by galactic cosmic rays. The dependence of the fall-out rate of atmospheric cosmogenic 36Cl on geomagnetic latitude and solar activity is calculated.

An enriched 58Ni sample has been irradiated with thermal neutrons together with an enriched 54Fe target. After chemical purification of the nickel sample, the produced radioactivities of 59Ni and 55Fe were measured with a silicon detector. The half-life of 59Ni has been deduced to be 108,000 ± 13,000 years. This halflife is larger than the commonly adopted half-life value of 76,000 ± 5000 years but is in full agreement with 59Ni concentration and activity measurements of the meteorite Admire. With accelerator mass spectrometry, the cross-section of the reaction 60Ni(n,2n)59Ni for 14.8 MeV neutrons has been measured to be 410 ± 100 mb.

Small concentrations of long-lived radioisotopes such as 59Ni are not necessarily easy to determine by AMS because of the background of stable isobars, in this case 59Co. The gas-filled Q3D magnetic spectrograph has been successfully used for isobaric separation. Additional suppression of non-isobaric background is accomplished by means of a Wien filter directly after the tandem and a highly sensitive time-of-flight measurement just before the spectrograph. Until now we have used these techniques for the radioisotopes 41Ca, 59Ni, 90Sr and 107Pd. The limits in sensitivity are at present between ~ 3 × 10−15 for 41Ca/Ca and ~ 1 × 10−8 for 107Pd/106Pd. Measurements have been performed on environmental, extraterrestrial and nuclear waste samples. Because of the insufficient sensitivity for measurements of very low concentrations with the existing Q3D, a dedicated gas-filled magnet with a deflection angle of 135° is now under construction.

The Cross section of the reaction 60Ni(n,2n)59Ni for 14.8 MeV neutrons has been determined to be (410±120) mb by measuring the contents of 59Ni in a fast neutron irradiated nickel foil via accelerator mass spectrometry (AMS). This new cross section is 4 times larger than the value of 100 mb as reported in literature. The half-life has been deduced to be (9.5±2.5)x104 y by using the result of a radioactivity measurement of 59Ni produced by thermal neutrons in the 58Ni(n,γ)59Ni reaction.