The local dynamics of 1,4 polybutadiene below and above the merging of
the alpha- and beta-relaxations have been investigated by means of Ne
utron Spin Echo. At temperatures below the merging, the dynamic struct
ure factor can be described by considering localized motions on a leng
th scale of 1.5 Angstrom for the beta-process with the barrier distrib
ution obtained from dielectric spectroscopy. Above the merging of the
alpha- and beta-relaxations, the experimental data have been successfu
lly described by assuming that both processes are statistically indepe
ndent.