Calorimetric Particle Detectors Research Articles

Electron–proton separation in calorimetry experiments directly measuring the composition and energy spectrum of cosmic rays

Calorimetric particle detectors that play an important role in high-energy cosmic-ray balloon and satellite experiments not only have the major task of measuring energy but also face the problem of identifying electrons and protons. This problem is usually solved by measuring the longitudinal and traverse shower profiles and the total energy release in the calorimeter, using the fact that electromagnetic and hadronic showers differ in their spatial and energy distributions. In this paper, electron and proton identification methods for different types of calorimeters used in cosmic-ray balloon- and satellite-borne experiments are discussed.

Calorimetric Detection of X-Rays

During the past 15 years a broad range of cryogenic particle detectors have been developed primarily for use in astro-particle physics, nuclear physics and material science. Among these, calorimetric detectors play an important role. In particular, micro calorimeters have proven to be a suitable tool for the detection of x-rays. We will discuss the concept of calorimetric particle detectors and the results for x-ray detection obtained with different types of calorimeters.

Low-energy X-ray detection in cryogenic detectors with tungsten thermometers

In the course of our development of calorimetric particle detectors with superconducting phase transition thermometers, we have succeeded in depositing epitaxial α-tungsten films on sapphire which have critical temperatures T c near 15 mK. To our knowledge this is the first time that the T c of bulk tungsten has been observed in thin films. Such films used as thermometers are very sensitive and provide good energy resolution: with 4 g and 32 g sapphire crystals energy resolutions of better than 100 eV (FWHM) for 1.5 keV X-rays have been achieved.

Physics and performance of calorimetric particle detectors with dielectric absorbers and superconducting phase transition thermometers

We present results obtained with detectors consisting of dielectric absorber crystals and superconducting phase transition thermometers made of Ir/Au bilayers. With a 31 g sapphire crystal and an Ir/Au thermometer operated at 45 mK we have obtained an energy resolution of 220 eV (FWHM) for collimated 5.9 ke V X-rays. To explain the measured pulse shapes we have developed a model which includes the effect of non-thermal phonons. Results obtained previously with a 18 g Si absorber and an Ir/Au thermometer with broad transition allowed checking this model over a wide temperature range. A heater experiment performed with this calorimeter provides further support of our model.

Superconducting tungsten films for use as phase transition thermometers for calorimetric detectors

To improve the sensitivity of calorimetric particle detectors we want to produce low-Tc superconducting thin films to be used as phase transition thermometers. We have succeeded in depositing epitaxial α-tungsten films on sapphire which have critical temperatures Tc near 15 mK. To our knowledge this is the first time that the Tc of bulk tungsten has been observed in thin films. Such a film has been produced on a 4 g sapphire crystal and operated as a calorimeter, giving an energy resolution of 75 eV (FWHM) for 1.5 keV X-rays.

Superconducting thin film thermometers for calorimetric particle detectors

At the Max-Planck-Institut and the Technical University of Munich thin film thermometers for calorimetric particle detectors with applications in elementary particle physics are being developed, using superconductors operated at their transition from the normal to the superconducting state. In this region a temperature change results in a change in resistance, which is measured. We are trying to produce tungsten thermometers (α structure) which should have a critical temperature of 15 mK. In order to avoid a contribution from ß-tungsten, which has a critical temperature of several kelvins, we grow α-tungsten epitaxially on (1 1 02) sapphire. The achievement of epitaxial growth is shown by X-ray diffraction. Up to now no superconductivity was observed in epitaxial films. We attribute this to the presence of an iron contamination, detected by secondary-ion mass spectrometry, at the interface to the substrate. A polycrystalline α-tungsten film, which was evaporated at lower substrate temperatures without baking of the system, showed a superconducting transition at 15 mK.

Calorimetric particle detectors with superconducting transition edge thermometers

The author discusses the development of calorimetric detectors utilizing large absorber crystals coupled to superconducting transition edge thermometers. At low temperature, high energy resolution results from the low detector heat capacity and the strong temperature dependence of the resistance of the thermometer at the normal/superconducting phase transition. The transition edge thermometer is a thin film at very low T/sub c/ superconductor deposited directly on the absorber. Results from two detectors yielding excellent energy resolution are presented. One of these detectors was fabricated with an Ir strip thermometer, and the other with an Ir/Au proximity effect bilayer. Detailed studies have resulted in a model which will be used to optimize future detectors. >

Calorimetric particle detectors with superconducting absorber materials

Abstract We use massive superconducting absorbers made of molybdenum and vanadium as low temperature calorimetric particle detectors. The high resolution of our thermometry system, consisting of a superconducting phase transition thermometer monitored with a dc-SQUID, enables us to detect α and γ particles with large single crystals. Heat pulses generated by passing current through a metal film on the surface of the crystal are used to study the response of the calorimeters. With a 35 g molybdenum single crystal we obtain an energy resolution of 10% FWHM on 5.8 MeV α particles at an operating temperature of 120 mK. The observed temperature rise of 1.2 μK is a factor of 8 less than expected from the calculated heat capacity. Using a 15 g vanadium single crystal, the energy resolution on 5.8 MeV α particles is 1.2% FWHM. In this case, the pulse height of 6.1 μK is a factor of 8 smaller than expected from the calculated heat capacity. A possible reason for the large deviations from the expected heat capacity is the presence of hydrogen dissolved in vanadium. Impurities and defects on the surface of the crystals probably contribute also to the heat capacity. The pulse shapes of all observed events are very similar, whether they are created by absorption of α or γ radiation or by an electrically created heat pulse, and consists of two exponential decaying parts. A comparison of the pulse heights of heater and radiation pulses leads us to the conclusion that all the energy deposited in the absorber crystal is converted into phonons.

Tests on low temperature calorimetric detectors for dark matter experiments

Tests are reported on low temperature calorimetric particle detectors consisting of Si and LiF crystals of mass 1–32 g fitted with commercial Ge temperature sensors, operating in the temperature range 50–70 mK. The objective was to demonstrate energy thresholds in the 1–10 keV range for dark matter detection. Using the energy spectra from 57Co and 137Cs photon sources for calibration, the measured RMS energy sensitivities were 1.5 keV in 1 g Si, 2.5 keV in 4 g Si, 4 keV in 8 g LiF, and 12 keV in 32 g LiF. Spectra were also observed for the photon and cosmic ray muon background, and for thermal neutron reactions in LiF. In all cases, observed energy spectra and absolute event rates were in agreement with Monte Carlo estimates, showing that the whole crystal volume was uniformly sensitive. Energy calibration and operating conditions remained stable with time and thermal cycling.

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

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 μK.

Voltage-assisted calorimetric ionization detector

A new approach to ionizing radiation detection is proposed. The amount of ionization produced in a detector medium is measured by the heat generated as the charged carriers are drifted across the device under an applied voltage. The amount of energy generated can be orders of magnitude larger than that deposited by the radiation itself. A dramatic increase in detector mass can be achieved compared to simple calorimetric particle detectors for equivalent energy thresholds. It is possible to obtain a sensitivity level sufficient for single-carrier detection. The principle of operation has been demonstrated with an experimental device operated at a temperature of 1.8 K, and improved performance is expected at lower temperatures.