SFQ digital signal processing circuits for multi-quantum beam detectors using STJ array with neutron absorbers

We studied multi-quantum beam detectors using a superconducting tunnel junction (STJ) array with neutron absorbers. Using a neutron absorber for each of the STJs, we expected the STJ detector to exhibit a high spatial resolution and high detection efficiency for neutrons as well as radiative beams such as X-rays. To obtain diffraction patterns of the X-ray and neutrons, we propose the use of a multi-quantum beam detector using an STJ array and single flux quantum (SFQ) signal processing at low temperature because of its high-speed and low-power operation. The kinetic energy is determined for individual neutrons using time-of-flight-methods that employ SFQ time-to-digital converters (TDCs). To separately detect α-particles and γ-ray particles that are produced by the nuclear reaction between neutrons and boron, and X-ray photons, excess quasi-particle currents of the STJ detectors are processed by V/F type analog-to-digital converters and T-FF binary counters using SFQ digital circuits. To obtain the multiplexed readout of an STJ detector array, we designed a current bias switching circuit controlled by an SFQ driver for time-domain multiplexing. We designed the main circuits for this SFQ signal processing system and fabricated them using the ISTEC SRL Nb standard process II (STP2).