  We report new measurements of the total cross section for the 3H(p,n)3He
reaction from threshold (Ep=1.02 MeV) to Ep=4.5 MeV. The experiment utilized
specially prepared Ti-3H targets, and neutrons were detected using a 4-pi
detector. A weak resonant structure due to an excited state in 4He is observed
which was not seen in previous cross section measurements. A new expression for
the 3He(n,p)3H thermonuclear reaction rate for temperatures below 10 GK is
presented which will allow for more accurate calculations of the yields of
light elements produced by big-bang nucleosynthesis.
