Further developments of series-connected superconducting tunnel junction to radiation detection

Abstract

One of the promising radiation detection devices for various practical applications is the series-connected superconducting tunnel junction (STJ) detector. In this article, interesting topics of the detectors are described since our previous work: e.g., more than two order higher detection efficiency compared with single STJ detectors, high count rate detection, and position resolution. Detectors were cooled to 0.35–0.4 K by means of a convenient He3 cryostat. The 5.9 and 6.5 keV x rays from Fe55 are separated by a detector specially designed for x-ray detection. The possible count rate of the series-junction detector estimated from the shaping-time constant applied in the measurements is high, e.g., over 104 counts per second. 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 radius of 1.1 mm. The position resolution of series junctions improves the energy resolution. A new type series-connected STJ detector is also proposed, i.e., the dispersed multitrap series-junction detector, for further improvement of detection efficiency and energy resolution.

An introduction to superconducting tunnel junction detectors

“…When an STJ detector consists of n series and m parallel STJs with an area of S/nm, C eff also takes the minimum value 2 Sc 0 C 0 1/2 for n D Sc 0 /C 0 1/2 independently of m. One of the merits of series-junction detectors is the flexibility in the choice of the size of the junctions. 30,37 Figure 10 shows the minimum value of C eff of a seriesjunction detector and the capacitance Sc 0 C C 0 of a singlejunction detector n D 1 as functions of total barrier area S for the case that c 0 D 6 µF/cm 2 and C 0 D 20 pF. For example, when it is assumed that Q of an STJ detector is 1000 times larger than those of semiconductor detectors and also that C C C 0 of a semiconductor detector for low-energy radiation is 20 pF and that of a semiconductor for high-energy radiation is 200 pF, the maximum permissible C eff of STJ detectors that have better S/N than semiconductor detectors is 20-200 nF because the signal voltage V S is given by Q/C eff .…”

The Effect of X-Ray Irradiating Superconducting Tunnel Junctions on<tex>$rm Al_2rm O_3$</tex>and<tex>$rm LiNbO_3$</tex>Substrates

“…We noticed that the phonon has a long mean free path with a several mm in a sapphire substrate [5] and can breaks Cooper pair. As phononmediated method, we used substrate of and which is high absorption material for low energy photon and fabricated STJ on it.…”

A grazing-incidence reflectometer for BL-39XU at SPring-8

“…Initially, an Si(Li) detector was used, but in the future a superconductor tunnelling junction detector (Kurakado et al, 1997) of a crystal analyser may be used instead. However, for X-ray re¯ection a wide dynamic range is important and an ionization chamber or an APD detector is used.…”