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Our matrix-assisted laser desorption/ionization (MALDI) mass spectrometer based on Al superconducting tunnel junctions (STJ) allows us to detect macromolecules in a way which is mass independent. However, the laser light (UV or IR) used to desorb the molecules reflects onto the STJ (in our case Al/Al–O x /Al junctions), heating them up, inducing a lower signal. In order to reduce this thermal recovery time, a new kind of substrate has been developed: a polyimide film, 1.5 μm thick, supported on a copper disc (o = 25 mm). The heat transfer is thus much more rapid, leading to a better performance at short flight times (

Cryogenic particle detectors have been proposed as alternative detectors for heavy molecule mass spectrometry [1] . The concept has been demonstrated by various groups in the last 3 years [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] . The single-molecule detection efficiency is independent of mass and close to the geometrical beam coverage. In addition, the charged state of the macromolecule can be determined by the pulse height of the cryodetector signal [7] . In this work, we present results from aluminium junctions (50 μm×400 μm) cooled by a dilution refrigerator. The Al-junction detectors were exposed to 6 keV X-rays from a 55 Fe source and to a variety of macromolecules, including IgG and polyethylenglycols (PEGs). Identical samples have been measured with a conventional secondary electron multiplier detector, allowing a sensitivity comparison. Our data, combined with measurements from other groups, suggest that the MALDI extraction does not affect too much the sample mass distribution, and that secondary electron detector sensitivity decreases with decreasing molecule velocity as exp(−(v/v0)3.5) with v0 being of the order of 50 km/s.

We set up a prototype for a new cryogenic particle detector. Due to its predicted amplification mechanism, such a bolometer may allow the construction of large volume detectors with the high-energy resolution of small cryogenic devices. These could be used in double beta decay or dark matter search experiments. The development of the different parts of this detector will be described, specially the production of the necessary high-quality superconducting microwave cavities.

The drift properties of tetrafluoromethane, CF4, studied for the first time up to a pressure of 5 bar and over a 20 cm drift distance, are presented. The aim of this research is to check the feasibility of a ν c e − scattering experiment sensitive to a neutrino magnetic moment down to a few 10−11 Bohr magnetons. This project and its motivations are also described.

Nonthermal phonons produced by X-ray and alpha particle absorption in silicon were detected with superconducting Sn/SnO x /Sn tunneling junctions. The correlation of signals induced by phonons from the substrate in two closely spaced junctions shows structures indicative of an anisotropic propagation of the non-thermal phonons. Taking into account the geometrical collection efficiency of the small-area junctions, more than 60% of the energy deposited in the crystal is converted into excess quasiparticles.

The microwave enhanced bolometer is a proposed cryogenic detector with an amplification mechanism. It consists of a crystal covered with a superconducting film exposed to a microwave flux. Incident particles will create nonthermal phonons in the crystal which then produce excess quasiparticles in the film. Those quasiparticles lead to microwave absorption in the film and a subsequent heating of the entire bolometer. In this way the energy deposited by a particle in the crystal could be amplified linearly by gains of up to 104. This would make possible bolometers of several kilograms with an excellent energy resolution which could be used for dark matter search or double beta decay experiments.

A fast current discriminator, based on Josephson junctions, has been developed to boost the performance of novel type of superconductive detectors in time-of- flight mass-spectrometers. The Josephson discriminator could greatly improve the mass resolution in such machines, and it is technologically compatible with the proposed superconductive tunnel junction detector. The effect of intrinsic thermally induced fluctuations in such a device has been investigated to identify the possible operating ranges, in terms of temperature, geometry and materials concerned. Experimental results on the feasibility of the proposed device are also reported.

We study the production of single γ, e and μ at high πt using the high energy data of the Mark-J detector at PETRA. We find good agreement with QED. We give mass limits of the SUSY particles γ , v , e and W studying the associated production of W and ẽ and radiative production of pairs of γ or v in three-body reactions.

The Mark J Collaboration at the DESY e/sup +/e/sup -/ collider PETRA presents results on the electroweak reactions e/sup +/e/sup -/..--> mu../sup +/..mu../sup -/tau/sup +/tau/sup -/,..mu../sup +/..mu../sup -/..gamma.., and e/sup +/e/sup -/..mu../sup +/..mu../sup -/. The c.m. energy range is 12 to 46.78 GeV. In the ..mu../sup +/..mu../sup -/ and tau/sup +/tau/sup -/ channels the total cross sections and the forward-backward asymmetries are reported and compared with other experiments. The results are in excellent agreement with the standard model. The weak-neutral-current vector and axial-vector coupling constants are determined. The values for muons and tau's are compatible with universality and with the predictions of the standard model. In the ..mu../sup +/..mu../sup -/..gamma.. channel, all measured distributions, including the forward-backward muon asymmetry, are in excellent agreement with the electroweak theory. Our data on the two-photon process, e/sup +/e/sup -/..mu../sup +/..mu../sup -/, agrees with QED to order ..cap alpha../sup 4/ over the entire energy range and the Q/sup 2/ range from 0.7 to 166 GeV/sup 2/.

In a superconducting detector, the energy resolution is expected to be superior than in a semiconductor detector, owing to the thousand times smaller energy gap Δ. The performance of Sn/Sn‐oxide/Sn tunneling junctions (operated in the Giaever mode at T=0.32 K) exposed to 6‐keV x‐ray photons of a 55Fe source is presented. The best energy resolution observed is 67 eV (FWHM). Extrapolating to vanishing electronic noise, an intrinsic resolution of 0.7% (FWHM) is obtained. This is an order of magnitude worse than expected from the statistics of the 2.5×106 primary electron charges produced, and is believed to be due to geometrical effects in the films. The energy response of the detector is nonlinear, owing to the self‐recombination of the free charge carriers. At a fixed bias voltage, the pulses generated in either film of the junction were observed to have the same sign. If the junctions are evaporated onto a silicon substrate, most of the pulses originate, via phonon backscattering, from x‐ray photons inter...

Numerical methods are developed for quick numerical computation of the Dirac electron-positron scattering matrix in timedependent electromagnetic fields. The procedure is based on angularmomentum decomposition of the Dirac equation and integration of the radial equations by a method of characteristics. The variation of the scattering data with the field strength is studied. This study is relevant to a nonperturbative approach to QED.

Results from realistic calculations of positron spectra generated in collisions of uranium on uranium are reported. The calculated spectra show a peak structure as it has been observed in experiments. The peaks are produced by the dipole field of the moving ions.

Refractory metal Nb/Al/Al-oxide/Al/Nb junctions are shown to be sensitive to 6-keV X-rays over the temperature range from 2.8 to 1.4 K. For such junctions, which have an observed minimum ionizing energy of 12 MeV, a limiting energy resolution of 8 eV is predicted. Currently an energy resolution of 250 eV is observed at 1.4 K which is primarily dominated by system electronic noise. The Nb-based junctions are shown to be very stable with respect to thermal cycling while the nonequilibrium physics can be simply scaled from the theory of Sn junctions. It is concluded that on-chip arrays having a broad band pass and good energy resolution should be feasible to construct. >

Since the resolution of a detector is limited by the statistics of the number of produced free charge carriers, a detector with a small minimal ionization energy per free charge is most favorable. The thousand times smaller gap of a superconductor (order of meV) compared to a semiconductor detector (Δeff(Si) = 2.94 eV, Δeff(Ge) = 3.6 eV)1 offers the possibility for particle detectors with an improved energy resolution2, 3, 4.

The limiting performance of a niobium based super conducting tunnelling junction are examined. The application of such devices as wide band high resolution X-ray spectrometers for use in high energy astrophysics is discussed. At 6 keV the energy resolution of an initial development device was 130 eV (FWHM) operated at 1.6 K. Means of improving this preliminary experimental resolution are outlined.