Differential polarization of photoneutrons from deuterium

The differential polarization of photoneutrons from deuterium has been measured at lab reaction angles of 45° and 90° for incident unpolarized photons in the energy range 7 to 30 MeV. The polarization is measured by observing the left-right asymmetry in the elastic scattering of neutrons from a liquid-helium polarimeter which is used in conjunction with a nanosecond time-of-flight spectrometer. At the lowest energies, the ¹²C(n, n)¹²C reaction is used as an analyser. The left-right asymmetry is determined by using the spin-precession method, recently developed for use with a continuous energy spectrum of neutrons. Two independent difference experiments are carried out using C²H₂-CH₂ and H₂O-H₂O targets in order to detect possible target-dependent systematic errors. Departures from the predictions of current theories of the photo-disintegration of the deuteron are observed at both reaction angles.