New method for precise determination of neutron beam polarization

We report the realization of a new method for precise determination of neutron beam polarization. The analyzing system utilizes two analyzers connected by a neutron guide which contains a spin flipper. The entire device can be rotated by 180°, thereby reversing the neutron trajectories through the device. The method has also been used to measure the neutron spin depolarization in the two analyzers. The depolarization is consistent with zero within an uncertainty of 10−3. As a consequence of this, two additional measurements, made with the device, yield values for the neutron polarization. The observed consistency of the three results suggests an accuracy for the method of 0.2%. We have used this technique to measure the polarization of the 50 × 100 mm2 cold neutron beam at the vertical channel of the WWR-M reactor with an accuracy of 0.2%.