Development and application of a neutron polarizing and focusing system based on magnetic field gradients

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In this study, we have developed a neutron polarizing and focusing device based on interaction between a neutron magnetic moment and a magnetic field, where we use quadrupole and sextupole magnets to polarize and focus neutrons, respectively. The device is considered useful for small angle polarized neutron scattering experiments with focusing geometry. The neutron polarizer is an extended Halbach-type quadrupole magnet with an inner diameter of 15 mm and length of 2,200 mm. The magnetic field gradient inside the quadrupole magnet was measured to be ~150 T/m. We set up the neutron polarizing and focusing device composed of the quadrupole magnet and two sextupole magnets at the beamline C3-1-2-1 of JRR-3, and performed pulsed neutron polarizing and focusing test. As the result, we could focus the pulsed neutrons in the wavelength range from 0.8 to 1.05 nm. The neutron polarizing and focusing device has been determined to be installed to a small angle neutron scattering instrument of J-PARC.