The parity nonconserving spin rotation of neutrons in the 0.734-eV p-wave resonance of 139 La was measured with the neutron transmission method. Two optically polarized 3 He cells were used before and behind a a 5-cm long 139 La target as a polarizer and an analyzer of neutron spin. The rotation angle was carefully measured by flipping the direction of 3 He polarization in the polarizer in sequence. The peak-to-peak value of the spin rotation was found to be (7.4 ± 1.1) × 10 −3 rad/cm which was consistent with the previous experiments. But the result was statisticallly improved. The s-p mixing model gives the weak matrix element as xW = (1.71 ± 0.25) meV. The value agrees well with the one deduced from the parity-nonconserving longitudinal asymmetry in the same resonance.

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