摘要 :
Turbulence in boundary layers of superfluid ~4He is studied using a vibrating wire. We developed a vortex filtering method for providing a superfluid practically free of remanent vortices in which a vibrating wire cannot generate ...
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Turbulence in boundary layers of superfluid ~4He is studied using a vibrating wire. We developed a vortex filtering method for providing a superfluid practically free of remanent vortices in which a vibrating wire cannot generate turbulence. Based on this superfluid, we find that vortex lines are nucleated by cooling through the superfluid transition and remain forming bridges between the wire and a surrounding wall. Vibration of the wire causes instability of bridged vortex lines, generating turbulence. Dense vortex lines produce the nonlinear modes of wire vibration, which is very sensitive to temperature, disappearing above 60 mK.
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摘要 :
This paper describes the 8-MeV neutron field where the neutrons are generated in the ~9Be(α,n)~(12)C reaction by bombardment of a beryllium target with a 2.4-MeV ~4He~+ beam from a Van de Graaff accelerator. The neutron field is ...
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This paper describes the 8-MeV neutron field where the neutrons are generated in the ~9Be(α,n)~(12)C reaction by bombardment of a beryllium target with a 2.4-MeV ~4He~+ beam from a Van de Graaff accelerator. The neutron field is being prepared for a new national standard on neutron fluence in Japan. Absolute measurement of the neutron fluence was taken using a proton recoil neutron detector, consisting of a silicon surface barrier detector with a polyethylene radiator. Neutron spectra were measured using a newly developed recoil proton spectrometer and a liquid organic scintillation detector. The gamma rays existing in the field were also characterised using a liquid organic scintillation detector. The ambient dose equivalents of the gamma rays were estimated to be <100 μSv at the neutron fluence of 10~7 neutrons cm~(-2).
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