Current-Biased Transition Edge Detector of $ \hbox{MgB}_{2}$ Nanowires for Neutrons: Imaging by Scanning Laser

The superconducting MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowire detector is biased by a current by a battery-class low voltage, and uses the nuclear reactions with a single neutron and the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B contained in MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detector consists of a 200-nm-thick MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film meander structure of 3 μm line width protected by 300-nm-thick SiO layer. We use enriched boron <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B to enhance the sensitivity. The thermal energy of 2.3 MeV released by the reaction <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> , α) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li gives 1.83 MeV to <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> He and 0.47 MeV to <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li. The energy dissipation in a restricted space causes a local resistive state in the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .