A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La

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 + gamma experiment at LANSCE. The elements of the polarized neutron beam, including a polarized He-3 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-35, Cd-113, and La-139 targets. Upper limits on the parity-allowed asymmetry s(n) (.) (k(gamma) x k(n)) were set at the level of 7 x 10(-6) for all three targets. Parity-violating asymmetries S-n (.) k(gamma) were observed in Cl-35, A(gamma) = (-29.1 +/- 6.7) x 10(-6), and La-139, A(gamma) = (-15.5 +/- 7.1) x 10(-6), values consistent with previous measurements. (C) 2003 Elsevier B.V. All rights reserved.