Polarization of Photoneutrons Produced from Deuterium by 2.75-MeV Gamma Rays

Abstract

An earlier experiment has been modified by the addition of a spin-precessing solenoid to permit an improved measurement of the polarization of the neutrons from photodisintegration of deuterium. Monoenergetic 2.75-MeV gamma rays were obtained from ${\mathrm{Na}}^{24}$ and the neutron polarization was analyzed by scattering from magnesium. The polarization normal to the reaction plane was measured for $\gamma -n$ laboratory angles from 30 to 150°. Empirical corrections were derived for neutron scattering in the deuterium source as well as in the Mg analyzer. Within the errors the polarization is found to be symmetric about 90°, consistent with the absence of noncentral forces. The magnitude is, however, (12±7)% smaller than that calculated by Kramer from $E1-M1\mathrm{}$ interference using effective-range theory. A major source of uncertainty in the experiment is the analyzing power of Mg. For a $\gamma -n$ laboratory angle of 90°, the neutron polarization was also determined in the direction of the incident gamma ray. The result $P<\mathrm{}0.01\mathrm{}$ is consistent with the conservation of parity in the reaction.