Experimental Apparatus and Design for Parity-Odd Asymmetry Measurement in ¹³⁹La

The NOPTREX collaboration plans to conduct a sensitive search for time reversal violation in polarized neutron transmission through polarized ¹³⁹La by taking advantage of the very large amplification of symmetry-violating effects already measured in the 0.734-eV p-wave resonance of ¹³⁹La. As a step toward this experiment we are remeasuring parity violation in n + ¹³⁹La on this resonance. We use two unpolarized ¹³⁹La targets with a neutron spin flipper in-between to do this. The first ¹³⁹La target polarizes the neutron beam and the parity-odd transmission asymmetry is measured by transmission through the second ¹³⁹La target. We aim for 1% precision on the ~10% P-odd asymmetry at the resonance peak. I will describe the major components of the apparatus that I designed and constructed: the ¹³⁹La cryostats and thermometry; a support structure for the cryostats, neutron spin flipper, neutron beam monitor, and beam collimators; and the shielding enclosure for the ⁶Li current-mode neutron transmission detector.