10 09 v 1 8 J an 2 00 4 A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35 Cl , 113 Cd , and 139

An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming −→n + p → d + γ experiment at LANSCE. The elements of the polarized neutron beam, including a polarized He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on Cl, Cd, and La targets. Upper limits on the parity-allowed asymmetry sn · (kγ × kn) were set at the level of 7× 10 for all three targets. Parity-violating asymmetries sn · kγ were observed in Cl, Aγ = (−29.1 ± 6.7) × 10, and La, Aγ = (−15.5 ± 7.1) × 10, values consistent with previous measurements.