Masuma Ahmed

The asymmetry of polarized neutrons scattered elastically from (‘209)Bi has been measured as a continuous function of neutron energy from 2 to 5 MeV, and at scattering angles between 3(DEGREES) and 30(DEGREES). The primary, unpolarized neutrons were generated at the Yale University Electron Linear Accelerator by the photodisintegration of natural lead. The polarized beam was produced by scattering elastically a fraction of these photoneutrons from a graphite cylinder at a reaction angle of 50(DEGREES) (lab) along a 15-meter flight path. The polarized beam was scattered from a bismuth target and the asymmetry of the scattered neutrons determined with an array of plastic scintillators. The magnitude of the polarization of the beam was measured in a separate, true double-scattering experiment. Neutron energies were determined with good resolution using a nano-second time-of-flight spectrometer. The generalized neutron spin precession method was used to reduce the systematic errors to less than two percent in the energy range between 2.3 and 3.3 MeV. Using a Monte-Carlo method, the measured asymmetries were corrected for finite geometry and multiple scattering effects. The energy-dependent data were analyzed using an optical potential, including the Mott-Schwinger interaction, and an optimum set of parameters obtained. Using this set, the sensitivity of the data at angles below 10(DEGREES) to different values of the neutron electric polarizability (alpha)(,n) was investigated, and a minimum value in (chi)(‘2) was obtained for (alpha)(,n) = (7 (+OR-) 20 (+OR-) 14) x 10(‘-42)cm(‘3). The value of (alpha)(,n) was found to lie within the range -1.3 x 10(‘-41) cm(‘3) < (alpha)(,n) < 2.7 x 10(‘-41)cm(‘3) with a sixty eight percent confidence level. This is the first limit to be set on this fundamental quantity from studies of polarization effects in neutron-nucleus scattering. The limit is smaller, by an order-of-magnitude, than two earlier estimates,(‘77,80) obtained from measurements of the differential cross section of fast neutrons elastically scattered from heavy nuclei at small angles. It is consistent with an estimate made from an analysis of the angular distribution of neutrons scattered from lead in the keV-region(‘15). The present limit also is consistent with the prediction of meson-theoretic and non-relativistic quark models, but is not consistent with the value calculated using a non-linear electrodynamic model.