Position Dependent Response of Superconducting MgB2 Neutron Detectors Studied by Pulsed Laser Irradiation

The MgB2 detector consists of 200 nm thick MgB2 thin film meander structure of 3 μm line width protected by 300 nm thick SiO layer. The electrical connections were provided by 150 nm thick Nb. The devices were placed in a 4 K refrigerator to investigate the behavior at temperatures below Tc. The position-dependent response of the MgB2 detector can be investigated by scanning a laser spot with the aid of the XYZ piezo-driven stage and an optical fiber with a focusing lens. We found that the inhomogeneity in a detector is very critical to specify the detection efficiency since the detector has the sensitivity only in a narrow temperature regime near Tc.