LOW-FREQUENCY VIBRATIONS IN POLYETHYLENE AT 300 DEGREES 77 DEGREES AND 4.2 DEGREES K

The absolute neutron scattering cross sections of oriented polyethylene have been measured at temperatures of 300°, 77°, and 4.2°K using the MTR phased chopper velocity selector. Low incident energies were used to optimize the energy resolution. The target was oriented such that the longitudinal and transverse cross sections could be observed simultaneously in different scattering angles. Data are presented in the form of absolute scattering cross sections and are also shown converted to the amplitude weighted directional frequency spectra. The conversion to frequency spectra includes use of measured Debye-Waller coefficients. Strong singularities are observed at phonon energies of 65, 25, 15.5, 12, and 5.6 meV.