Measurement of the absolute neutron beam polarization from a supermirror polarizer and the absolute efficiency of a neutron spin rotator for the NPDGamma experiment using a polarized ${}^3$He neutron spin-filter

Abstract

Accurately measuring the neutron beam polarization of a high flux, large area neutron beam is necessary for many neutron physics experiments. The Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) is a pulsed neutron beam that was polarized with a supermirror polarizer for the NPDGamma experiment. The polarized neutron beam had a flux of $\sim 10^9$ neutrons per second per cm${}^2$ and a cross sectional area of 10$\times$12~cm${}^2$. The polarization of this neutron beam and the efficiency of a RF neutron spin rotator installed downstream on this beam were measured by neutron transmission through a polarized ${}^3$He neutron spin-filter. The pulsed nature of the SNS enabled us to employ an absolute measurement technique for both quantities which does not depend on accurate knowledge of the phase space of the neutron beam or the ${}^3$He polarization in the spin filter and is therefore of interest for any experiments on slow neutron beams from pulsed neutron sources which require knowledge of the absolute value of the neutron polarization. The polarization and spin-reversal efficiency measured in this work were done for the NPDGamma experiment, which measures the parity violating $\gamma$-ray angular distribution asymmetry with respect to the neutron spin direction in the capture of polarized neutrons on protons. The experimental technique, results, systematic effects, and applications to neutron capture targets are discussed.

arXiv comment13 pages, 14 figures, 2 tables

References in corpus (7)

• Optically Polarized ${}^3$He
• Lattice QCD Calculation of Nuclear Parity Violation
• New measurement of the scattering cross section of slow neutrons on liquid parahydrogen from neutron transmission
• Fundamental Neutron Physics Beamline at the Spallation Neutron Source at ORNL
• High-Efficiency Resonant RF Spin Rotator with Broad Phase Space Acceptance for Pulsed Polarized Cold Neutron Beams
• Neutron Beam Effects on Spin Exchange Polarized He-3
• Neutron interferometric measurement of the scattering length difference between the triplet and singlet states of n-${}^3$He

Cited by in corpus (7)

• First Observation of $P$-odd $\gamma$ Asymmetry in Polarized Neutron Capture on Hydrogen
• First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on ${}^3$He
• A modular apparatus for use in high-precision measurements of parity violation in polarized eV neutron transmission`
• Neutron Polarimetry Using a Polarized 3He Cell for the aCORN Experiment
• Monte Carlo calculation and verification of the geometrical factors for the NPDGamma experiment
• Measurement of the Parity-Odd Angular Distribution of Gamma Rays From Polarized Neutron Capture on ${}^{35}$Cl
• Monte Carlo calculation of the average neutron depolarization for the NPDGamma experiment