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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.

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.

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. >

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.