Nuclear orientation facility for the study of the angular distribution of γ radiation and β particles emitted by polarized nuclei

Abstract A nuclear orientation facility using a 3 He/ 4 He dilution refrigerator and ferromagnetic host foils for the polarization of radioactive nuclei is described. A unique feature of this facility is the capability of studying the directional distribution of β particles ( E β > 100 keV) emitted by polarized nuclei over a wide range of angles without significant deflections of the β particle trajectories. Closed magnetic loops and high permeability source host foils are critical elements of the design that reduce stray magnetic fields in the region between the β source and the detector. This orientation facility has been used to completely map out the angular distribution of β particles emitted by polarized 60 Co nuclei. The observed angular distribution is in excellent agreement with the expected [1 + AP ( v / c cos θ ) dependence from the V-A theory of weak interactions. The experimental value of the β-asymmetry parameter ( A exp = −1.01 0.02) is consistent with maximal parity violation ( A theory = −1).