A new scheme is proposed for achieving a closed, homogeneous, and isotropic optical circuit necessary for high-accuracy optical-current sensors. It makes use of a single solid polygonal solid with reflection surfaces coated by quarter-wavelength dielectric thin-film layers for the Faraday cell. We derive the design principle and show numerically its applicability in various Faraday materials. The cross talk with the surrounding current is investigated in particular detail both theoretically and experimentally. In the example experiment with a SF57 Faraday material, a low cross talk is demonstrated for nearby currents.

For rapid detection and characterization of radioactive materials in rather large area, we have developed a portable 4π sensitive γ-ray imager based on Compton imaging. Using a prototype based on a 3D pixel array CdTe detector, radioactive source positions such as 137 Cs and natural uranium metal sample were identified.

A new type of Faraday effect current sensor consisting of a single SF57 glass block having dielectric multilayer mirrors coated to have polarization-preserving perfect reflection and containing no parasitic field sensitive parts is developed. A good isolation froffi the external current and field is demonstrated.

This paper describes the 8-MeV neutron field where the neutrons are generated in the (9)Be(alpha,n)(12)C reaction by bombardment of a beryllium target with a 2.4-MeV (4)He(+) 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 microSv at the neutron fluence of 10(7) neutrons cm(-2).