We present an evaluation of the 1-loop prefactor in the lifetime of a
metastable state which decays at finite temperature by bubble nucleation. Such
a state is considered in one-component phi^4 model in three space dimensions.
The calculation serves as a prototype application of a fast numerical method
for evaluating the functional determinants that appear in semiclassical
approximations.Comment: DO-TH-93/18, 15 pages, 11 Figures available on request, LaTeX, no
macros neede