Current-Biased Transition Edge Detector of \hbox Nanowires for Neutrons: Imaging by Scanning Laser

The superconducting MgB 2 nanowire detector is biased by a current by a battery-class low voltage, and uses the nuclear reactions with a single neutron and the 10 B contained in MgB 2 . The MgB 2 detector consists of a 200-nm-thick MgB 2 thin film meander structure of 3 μm line width protected by 300-nm-thick SiO layer. We use enriched boron 10 B to enhance the sensitivity. The thermal energy of 2.3 MeV released by the reaction 10 B( n , α) 7 Li gives 1.83 MeV to 4 He and 0.47 MeV to 7 Li. The energy dissipation in a restricted space causes a local resistive state in the MgB 2 wire, which yields a subtle change in bias current. Through a mutual inductance connected in series with current-biased detector, we are able to measure the event as a voltage pulse. The position-dependent response of the MgB 2 detector is investigated by scanning a focused laser spot with the aid of an XYZ piezo-driven stage and an optical fiber with a focusing lens. A clear two-dimensional imaging pattern of the sensor signal well corresponds to the detector geometry. According to our results, the inhomogeneity and position-sensitive nature of the detector are supposed to be critical in governing the detection efficiency of the current-biased transition edge detector, which works only in the narrow temperature regime near T c .