Masahiro Ukibe

High resolution X-ray detection by Nb-based STJ and 4-JFETs low noise amplifier

Abstract We have made up a low noise charge sensitive amplifier with cooled 4-JFETs for a large area superconducting tunnel junction (STJ). These JFETs were operated at about 130 K. Each JFET (2SK190) dissipates about 15 mW. A high energy resolution of 73 eV for 5.9 keV X-rays and 61 eV for pulser signals have been achieved with a 178 μ m × 178 μ m Nb/AlAlO x /Al/Nb STJ having a junction capacitance of 1900 pF.

Characteristics of Ti films for transition-edge sensor microcalorimeters

Abstract We are developing X-ray microcalorimeters using superconducting transition-edge sensors (TESs), which can be operated at relatively high base temperatures of a 3 He cryostat. For this purpose, we have selected Ti films to be used as TESs. The Ti films were deposited on different substrates by RF-sputtering. It was found that the superconducting properties of the Ti films depended on Ar pressure, film thickness, and substrate surface roughness.

A LOW-NOISE CHARGE-SENSITIVE PREAMPLIFIER FOR AN X-RAY DETECTOR OF A NB-BASED SUPERCONDUCTING TUNNEL JUNCTION

Abstract A low-noise charge-sensitive preamplifier with cooled 4-JFETs was developed for an X-ray detector of a Nb-based superconducting tunnel junction with a large capacitance and a low leakage current. The low-noise characteristics for a wide range of shaping times were obtained by using a selected JFET, 2SK 190 in the first stage of the preamplifier. A new formula to simulate the preamplifier noise was developed and applied to the optimization of preamplifier design. A high-energy resolution of 66 eV for 5.9 keV X-ray and 51 eV for pulser signals was obtained by using the optimized preamplifier with an X-ray detector of a 178 μ m × 178 μ m Nb/Al-AlO 2 /Nb superconducting tunnel junction with a junction capacitance of 1900pF and a bias current of 1.44nA.

X-ray Detection Characteristics of Nb-Based Superconducting Tunnel Junctions

Detailed X-ray detection characteristics for Nb-based superconducting tunnel junctions (STJs) were measured with cooled 4-JFETs low noise charge sensitive amplifier that we developed. We studied the detection characteristics for a wide energy range of X-rays and signal production processes for quasiparticles in Nb-based SIS junction and substrate phonons, and phonon detection.

Quantitative Evaluation of the Quantum Efficiency of a Superconducting Tunnel Junction with the Multiple Scattering Process Model of Primary Photoelectrons

The electron multiple scattering process of primary photoelectrons generated absorbed X-rays was studied so as to developed a clear model of a signal producing process of a STJ, and the intrinsic peak efficiency P1 of the STJ was calculated as a function of X-ray energy. X-rays of 5 to 18 keV were measured by a 178 µm×178 µm Nb/Al-AlO2/Al/Nb superconducting tunnel junction with a Nb-electrode, 200nm thickness and the P1 agreed well with the measured one in X-ray energy range of 5 to 12 keV.