Superconducting MgB2 films as radiation detectors

The thermal response of a membrane-structured MgB2 film can be used to detect various sorts of radiations. High-quality MgB2 films were prepared by a sputtering technique. The MgB2 radiation detector consisted of an MgB2 thin-film meander line on a 0.5-mu m-thick SiN membrane. The detector devices were placed in a 4 K refrigerator, and the operating temperature was controlled at a certain temperature below T-c. Light from a 20-ps pulsed laser directly irradiated the MgB2 device; the end of the optical fiber was fixed in front of the device. An erbium-doped fiber amplifier (EDFA) and a GP-IB attenuator were used to control the laser power, and the output voltage was observed through a low-noise amplifier by using a digital oscilloscope. The output signals caused by thermal response were clearly observed. Systematic studies of the output signals were conducted, and effects of device design, dc bias conditions, bias temperature, and input laser power were considered. We report the out-of-equilibrium thermodynamics, which was investigated by means of extensive computer simulations based on the time-dependent Ginzburg-Landau equations, thermodynamics, and electrodynamics. Large-scale calculations were carried out under the realistic conditions of actual devices by using an Earth Simulator (ES). One attractive application is to use the device as a novel neutron detector by employing the B-10(n,alpha)(7) Li nuclear reaction with a local energy release of 2.3 MeV.