Polarization of Neutrons from the Photodisintegration of Deuterium

The polarization of neutrons photoproduced from deuterium at about 148° in the center-of-mass system was measured at four intervals in the photon energy range of 12.0-22.9 MeV in the laboratory system. The neutron polarization was analyzed in a low-pressure helium diffusion cloud chamber by scattering the neutrons and observing the left-right asymmetry in the helium gas nuclear recoils. This was achieved by photographing the individual recoils on film, then making measurements on the stereoscopically projected recoil track images, and finally subjecting the data to a maximum likelihood calculation. The flash photography of the random-scattering events was controlled by a photoelectric detection system: The cloud chamber was illuminated continuously with a slide projector light beam and a photomultiplier detected the reflected light from the formation of a densely ionizing track. The polarizations measured in the four photon-energy intervals of 12.0-12.9 MeV, 13.0-15.9 MeV, 16.0-17.9 MeV, and 18.0-22.9 MeV are -0.149±0.100, -0.198±0.086, -0.254±0.120, and -0.295±0.137, respectively. The polarization is defined to be positive in the direction of ${\mathrm{k}}_{\gamma }\times {{\mathrm{k}}_{n0\mathrm{}}}^{\prime }$ the directions of the incoming photon and outgoing photoneutron, respectively. The results are substantially in agreement with the polarization calculations by deSwart and Marshak and by Rustgi, Zernik, Breit, and Andrews.