G. Waysand

SIMPLE dark matter search results

We report an improved SIMPLE experiment comprising four superheated droplet detectors with a total exposure of 0.42 kgd. The result yields similar to factor 10 improvement in the previously-reported results, and-despite the low exposure-is seen to provide restrictions on the allowed phase space of spin-dependent coupling strengths almost equivalent to those from the significantly larger exposure NAIAD-CDMS/ZEPLIN searches. (c) 2005 Elsevier B.V. All rights reserved.

Expulsion of magnetic flux in a type-I superconducting strip

Abstract Flux expulsion in a type-I superconducting strip, induced by decrease of a perpendicular magnetic field following field increase-induced flux penetration, is observed by real time detection of the flux-induced voltage pulses. Three different expulsion regimes are identified, corresponding in general to the three initial regimes of flux penetration. The crossover field between two expulsion regimes is found to be associated with the change of nucleation mechanism at Hc2. Possible association of the expulsion onset with surface superconductivity and Hc3 is discussed. The results support the idea of existence of an energy barrier against flux expulsion.

About the world-wide magnetic-background noise in the millihertz frequency range

In the millihertz range, a single magnetometer can detect magnetic waves in the near-field regime. For such long wavelengths, it can measure the world-wide magnetic-background noise due to any charge displacement on Earth and within its environment. In this frequency band, the normal modes of the Earths free oscillations exist and when excited, they shake the air column above them, up to the ionosphere where the moving charges emit a magnetic fluctuation, via Amperes law. We show the magnetic-background noise spectrum obtained by an FFT analysis of 72 consecutive hours of magnetic-seismic calm. It is mostly due to vertical charge oscillations. Even in the absence of a quake larger than Mw= 5.2, spherical and toroidal modes are deected. Instrumental and analytical perspectives are discussed.

MCNP optimization of filtered neutron beams for calibration of the SIMPLE detector

We report an MCNP study of filtered monochromatic neutron beams of energies 25, 54 and 149 keV for response studies of a superheated droplet detector for the SIMPLE experiment. The results identify the importance of the detector temperature stabilizing water bath and the aqueous gel of the detector on the beam quality, in general agreement with recent measurements made on the thermal port of the Portuguese research reactor.

Beta Irradiation of a Geometrically Metastable Superconducting Strip Detector with a Magnetic Flux Penetration Read-Out.

Geometrical metastability, observed in superconducting type I tin flat strips, has been previously proposed as a principle for particle detection. The energy deposition of an incoming beta-particle induces the rupture of the metastability and consequently the penetration of multiquantum flux tubes into a superconducting tin strip. We present here the first absorption spectra from two beta sources, which demonstrate the linearity and energy-resolution of these detectors (presented at the 6th International Workshop on Low Temperature Detectors for Dark Matter and Neutrinos (LTD-6), Interlaken, Switzerland, Sept. 1995)Geometrical metastability, observed in superconducting type I tin flat strips, has been previously proposed as a principle for particle detection. The energy deposition of an incoming beta-particle induces the rupture of the metastability and consequently the penetration of multiquantum flux tubes into a superconducting tin strip. We present here the first absorption spectra from two beta sources, which demonstrate the linearity and energy-resolution of these detectors (presented at the 6th International Workshop on Low Temperature Detectors for Dark Matter and Neutrinos (LTD-6), Interlaken, Switzerland, Sept. 1995)

Response of a metastable superconducting grains suspension to irradiation by 35S decay electrons

Abstract We report a measurement of the energy loss spectrum of electrons in the beta decay of 35 S using a prototype detector composed of a suspension of 10–25 μm diameter tin grains at 2.3 K. Preliminary analyses suggests the capability of achieving sub-eV resolutions in such measurements, and that—contrary to conventional wisdoms—this is possible with both relatively large grains and a distribution of the grain sizes.

A new description of the behavior of metastable superconducting grains suspensions under irradiation

Intense or prolonged irradiation of suspensions of disordered Type I superconducting grains maintained in a superheated state creates a “hot border zone” below the normal superheated transition boundary. Subsequent increase of the applied magnetic field moves superconducting grains across the border into the zone, for which only thermal nucleation is possible until the highest local fields have again reached the usual superheated-normal transition value. This model suggests that, contrary to conventional wisdoms, energy resolution is possible with such detectors using both relatively large grains and size distributions.

SIMPLE limits on spin-dependent WIMP interactions

An improved SIMPLE experiment comprising four superheated droplet detectors with a total exposure of 0.42 kg.d yields ~factor 10 improvement in the previously-reported results. Despite the low exposure, the result provides restrictions on the allowed phase space of spin-dependent coupling strengths almost equivalent to those from the significantly larger exposure NAIAD-CDMS/ZEPLIN searches.

Study of a novel transition radiation detector utilizing superconducting microspheres for measuring the energy of relativistic high energy charged particles

Abstract In want of a detector capable of measuring accurately the energy of relativistic high energy charged particles, a novel transition radiation detector (TRD) utilizing superheated superconducting microspheres of tin of 22–26 μ m , 27–32 μ m and 32–38 μ m in diameter respectively has been constructed. For the purpose of enhancing the TR effect, the TRD is operated at ∼ 100mK. Test has been conducted in a high energy electron beam facility at the CERN PS in the energy range of 1–10 GeV showing an energy dependence of the TR X-ray photon produced and hence the value γ =E/mc 2 of the charged particle.

Response of a metastable superconducting detector to55Fe irradiation below 400 mK

We report a preliminary analysis of the irradiation of a suspension of superheated superconducting grains by55Fe at temperatures below 400 mK. The suspension comprised both Sn (20–25 micron) and Al (≤20 micron) grains in equal filling factors of 20%. The differential magnetic field sweep spectra exhibit a peak structure, which we discuss in terms of the absorption of the 6 keV Xray of the55Fe decay and secondary excitations.