Masahiko Kurakado

Progress in superconducting tunnel junction detectors

Superconducting tunnel junction (STJ) detectors have great potential as ultra-high energy-resolution detectors even at high count rates of over 10 4 counts per second. In fact, single-junction detectors showed energy resolutions of better than 30 eV for 5.9 keV x-rays, 6 eV for 277 eV x-rays and 0.2 eV for 2 eV optical photons. Series-junction detectors have much higher detection efficiencies than single-junction detectors. A series-junction detector equipped with a position-sensing mechanism has shown a position resolution of about 35 μm in a sensing area with a diameter of 2.2 mm. The position resolution can improve the energy resolution of the detector. This paper briefly reviews the main principles of and progress in STJ detectors and gives a perspective of these detectors.

An introduction to superconducting tunnel junction detectors

Superconducting tunnel junction (STJ) detectors have potential as ultra-high-energy resolution detectors. Recently, single-junction detectors, where radiation is directly absorbed and detected by an STJ, have shown much higher energy resolutions than semiconductor detectors even at high count rates of over 104 counts per second, e.g. resolutions of 12 eV for 5.9 keV x-rays, 6 eV for 277 eV x-rays and 0.2 eV for 2 eV optical photons. The energy resolutions of series-junction detectors, where radiation is absorbed by a single-crystal substrate and the resulting non-thermal phonons are detected by STJs connected in series on the substrate, are not yet better than those of semiconductor detectors but are improving rapidly. This paper briefly introduces some principles of STJ detectors and reviews their recent developments. Copyright

Two dimensional imaging by series-connected STJs with sapphire absorber

Abstract The position determination capability of the series-connected superconducting tunnel junctions (STJs) with Nb/Al/AlO x /Al/Nb junctions as a radiation detector is reported. Four groups of series-connected STJs are fabricated on a single crystal of sapphire substrate surrounding 3.5×3.5 mm 2 detection area. The signals detected by two STJs with 1.5 mm separation give a time delay caused by the propagation of phonons, and this enables us to measure the irradiated position. Using α -particles of 5.5 MeV , we clearly distinguished the incident positions with a potential resolution of 0.16±0.07 mm (FWHM). Directional dependence in the phonon propagation in the sapphire substrate is not detected.

Two-dimensional position resolution and correction of incidence position dependency of signal heights of series-junction detectors

A series-junction consists of Superconducting tunnel junctions (STJ) connected in series. The present series-junction detector has four serial junctions on the substrate. The sum of the four signal heights depends on the incidence position of radiations in the series-junction detector. The incidence position dependency of the signal heights deteriorates energy resolution. The two-dimensional position resolution was obtained by making use of the signal heights from the four series-junctions. It was developed that the correction method for the incidence position dependency of pulse height by making use of the position resolution in this study. It was confirmed that this method is useful to improve the energy resolutions of the series-junction detectors.

Characteristics of Superconducting series array tunnel junctions for heavy ions

Heavy ion detection experiments were carried out with superconducting series array tunnel junctions. /sup 40/Ar beam from linear accelerator was introduced to a cryostat and stopped in a substrate on which series array tunnel junctions were fabricated. An energy resolution of 4.2% was obtained for 191 MeV /sup 40/Ar, but linearity proved poor for energy ranges from 136 MeV to 191 MeV.

Measurements of the linearity of an STJ and position resolution of series-connected STJs

Abstract Superconducting tunnel junctions (STJ) have been developed mainly at high-resolution spectrometers for use in X-ray astronomy. A FWHM energy resolution of 112 eV at 5.9 keV is obtained using an STJ developed at Nippon Steel Corporation connected with a cooled FET (∼100 K). The pulse height of the signal is represented by a logarithmic function of energy based on consideration of the recombination of the quasi-particles in the junction. Experiments using series-connected STJs for an imaging radiation detector are performed. Both the pulse height and the rise time of signals from 241 Am α-particles indicate good position sensitivity with resolution less than 0.5 mm.