Measurement of the Polarization of Photoneutrons from Deuterium

Theoretical studies have predicted that the neutrons from the reaction $\mathrm{D}(\gamma , n)\mathrm{H}$ are polarized. At low gamma-ray energies, the polarization results from an interference between the electric and magnetic dipole transitions. We have measured the polarization of the photoneutrons produced from deuterium by the 2.75-Mev gamma rays of ${\mathrm{Na}}^{24}$. The photoneutrons were scattered from magnesium and the polarization determined from the left-right asymmetry using recent experimental results of Elwyn, Lane, and Langsdorf for the polarization-analyzing ability of magnesium. For gamma ray-neutron angles (center-of-mass) of 49.6°, 71.8°, 93.6°, 114.8°, and 135.7°, the neutron polarizations are found to be -0.34±0.05, -0.23±0.06, -0.22±0.06, -0.29±0.05, and -0.24±0.06, respectively, where positive polarization is taken to be in the direction of ${\mathrm{k}}_{\gamma }\times {\mathrm{k}}_n$. The results are in agreement with a calculation by Kramer in the effective-range approximation, assuming only dipole transitions and no noncentral forces.