The branching ratio $\frac{{\Gamma }_{\gamma 0}}{{\Gamma }_{\alpha }}$ for the $d+t$ reaction has been measured between deuteron energies of 45 and 146 keV. Pair-coincidence spectrometry and pulse-shape discrimination were employed to reduce the neutron effects in the NaI(Tl) gamma-ray detector. The branching ratio is found to be constant over the energy range of the measurements with a best value $\frac{{\Gamma }_{\gamma 0}}{{\Gamma }_{\alpha }}=(5.4\mathrm{}\pm 1.3)\times {10}^{-5\mathrm{}}$. This value is significantly greater than cluster-model calculations of the branching ratio.

• Received 22 June 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.767