F. Pröbst

Quasiparticle trapping in a superconductive detector system exhibiting high energy and position resolution

Abstract A new superconductive detector system employing quasiparticle trapping from a separate absorber into two superconducting tunnel junctions is investigated. The energy resolution for the 55Mn-Kα-energy (5.89 keV) is 60 eV (FWHM) and the position resolution was determined to be better than 5 μ over a sensitive length of 450 μm. A quasiparticle rejection efficiency of better than 99.6% was measured for a thick superconducting lead barrier between two superconducting tin absorbers.

Phase transition thermometers with high temperature resolution for calorimetric particle detectors employing dielectric absorbers

Abstract We describe a thermometry system for low temperature calorimetric particle detectors, consisting of a phase transition thermometer combined with a SQUID readout. Studies were performed of a cadmium phase transition thermometer attached to a 1.1 g silicon absorber. Operated at 455 mK an energy resolution of ΔE E = 1% for irradiation with 5.8 MeV α -particles was achieved. This resolution was limited by the data acquisition system used. We also studied an iridium thermometer attached to a 280 g sapphire absorber operated at 135 mK. This calorimeter exhibited an energy resolution of ΔE E = 1.2% for irradiation with 5.8 MeV α -particles. The change in temperature caused by the absorption of one α -particles was measured to be 4.5 μ K.

A new detector of nuclear radiation based on ballistic phonon propagation in single crystals at low temperatures

Abstract The absorption of 5.5 MeV α-particles in a silicon single crystal kept at T=0.38 K was detected by an array of superconducting tunnel diodes evaporated onto the surface of the crystal. Signals were mediated by phonons propagating ballistically within the crystal. The phon flux proved anisotropic due to phonon focusing effects. This anisotropy and the study of time resolved signal correlations between the diodes allowed us to distinguish two spots of α-absorption separated by 0.75 mm. This detection principle might be applicable in a variety of experiments in nuclear and elementary particle physics.

Recent developments in detector research

Recently developed methods of cryogenic particle detection and potential applications will be introduced. The main part of this article focuses on our experimental results on two different approaches of detecting nuclear radiation with superconducting tunnel junctions. The best energy resolution is obtained when the junction itself serves as absorber. Using Sn/SnOx/Sn tunnel junctions we obtained an energy resolution of about 90 eV for 6 keV X-rays up to now. The processes limiting the resolution of the present devices will be discussed. Larger absorber masses and position resolution are realized by an entirely new type of particle detector based on the detection of nonthermal phonons which are generated by the absorption of radiation within a single-crystalline absorber of dielectric material. We report on experimental tests of a detector composed of a silicon single crystal (size: 10 × 20 × 3 mm3) and of an array of superconducting Al/Al2O3/Al tunnel junctions evaporated onto the surface of the crystal, serving as phonon detectors. Pulse height analysis and the investigation of time differences between pulse onsets in different junctions are shown to yield information about the absorption point of α-particles.

Low temperature calorimeters

Abstract Properties of calorimetric detectors at low temperatures are discussed. Superconductors at the critical temperature used as thermometers and superconducting tunnel junctions are considered as sensors for energy absorption. The different mechanisms of detection are compared and eventually achievable sensitivities estimated.

Nonequilibrium phonon detectors

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 ballist...

Calorimeters with proximity-effect thermometers and lead and tin absorbers

Taking advantage of the low critical temperatures of proximity-effect phase transition thermometers, superconductors with low Debye temperatures can be used as absorber materials for calorimetric detectors. We performed experiments with lead and tin absorbers of a mass of about 1 g. The energy resolutions for 6 keV X-rays are 1000 eV and 230 eV FWHM, respectively. A model which includes the effect of both thermal and non-thermal phonons explains the measured pulse shapes. The observed heat capacity of the absorbers agrees with that given by the Debye law. A comparison of heat pulses and of radiation induced pulses shows a thermalization efficiency close to 100%. No evidence for trapping of energy as quasiparticles is observed.

Position sensitive detection of nuclear radiation mediated by non equilibrium phonons at low temperatures

Many experiments in nuclear and particle physics would benefit from the development of a device capable of detecting non-ionizing events with a low energy threshold. In this context, we report on experimental tests of a detector based on the registration of nonequilibrium phonons. The device is composed of a silicon single crystal (size: 20×10×3 mm3) and of an array of superconducting tunnel junctions evaporated onto the surface of the crystal. The junctions serve as sensors for phonons created by absorption of nuclear radiation in the crystal. We show how pulse height analysis and the investigation of time differences between correlated pulses in different junctions can be used to obtain information about the point of absorption.

Calorimetric Detectors at Low Temperatures

Properties of calorimetric detectors at low temperatures are discussed. Metastable superconductors, superconductors at the critical temperature used as thermometers and superconducting tunnel junctions are considered as sensors for energy absorption. The different mechanisms of detection are compared and eventually achievable sensitivities estimated.

TESTS OF A NONEQUILIBRIUM PHONON DETECTOR

Many experiments in nuclear and particle physics would benefit from the development of a device capable of detecting non-ionizing events with a low energy threshold. In this context, we report on experimental tests of a detector based on the registration of nonequilibrium phonons. The device is composed of a Silicon single crystal (size: 10 × 20 × 3 mm 3 ) and of an array of superconducting tunnel junctions evaporated onto the surface of the crystal. The junctions serve as sensors for phonons created by absorption of nuclear radiation in the crystal. We show how pulse height analysis and the investigation of time differences between correlated pulses in different junctions can be used to obtain information about the point of absorption.