Preliminary Experiment of Magnetic Imaging Using Polarized Pulsed Neutrons at HUNS

Abstract

Imaging using polarized neutrons is one of the most attractive techniques in the neutron imaging field, because of its capability to visualize magnetic field inside materials or spaces by analyzing neutron polarization. An advanced method, which can quantify the magnetic field by combining the time-of-flight method with a polarization analysis of pulsed neutrons, has been developed at J-PARC. To introduce this method to the compact accelerator-driven neutron source, we have started the magnetic imaging experiments at Hokkaido University Neutron Source (HUNS). Using an experimental system consisting of a pair of magnetic super-mirrors as a polarizer and an analyzer, a spin flipper, and a two-dimensional neutron detector, we obtained the polarization of 90% at the wavelength over 6 Å. The first demonstration experiments were performed for coil samples. As a result, an oscillatory behaviour of polarization depending on the wavelength due to the neutron spin's Larmor precession was clearly observed.

Polarization measurements in neutron imaging

“…ing. Like outlined earlier, the issue of the modulation of the polarization signal has been argued [10,49] and shown [15,[50][51][52][53] to be overcome by wavelengthdispersive measure ments constituting the potential of a ToF imaging approach in polarized neutron imaging. Because the net spin preces sion angle depends on the time the neutron spends in a field, the final polarization P i is an oscillating function of the wave length and hence also the time of flight (figure 4).…”

“…The wavelength tunable device typically provides wavelength resolutions Δλ/λ of a few percent in the cold neutron regime, depending on the mosaicity of the crystals used. Alternatively, a ToF approach can be chosen, as was proposed very early [48,49], to provide significant benefits at pulsed sources where it meanwhile has been applied [15,[50][51][52][53]. While the latter, providing polarization measurements at multiple wave lengths, has significant advantages for quantification, first the initial approach of monochromatic polarized neutron imaging shall be discussed.…”