Abstract
A precise determination of the energy of the neutrons from the deuteron-deuterium reaction has been made. The energy of the neutrons emitted in the forward direction to the 0.52-Mev deuterons which produced the disintegrations was found to be 3.58±0.03 Mev. The disintegration Q value of the reaction is 3.31±0.03 Mev. The mass of He3 calculated from this Q value is 3.01698±0.00006 mass units.