Calorimetric Determination of the Average Total Kinetic Energy of Fragments from Fission ofU235

The average kinetic energy of the fragments from thermal neutron fission of ${\mathrm{U}}^{235}$ has been redetermined calorimetrically; a value of 166±2 Mev is obtained, in excellent agreement with other measurements. The calorimeter and the method of correction for beta absorption are described. The number of fissions occurring in the samples was determined by a ${\mathrm{Mo}}^{99}$ radiochemical analysis which is described in detail. An improved value for the half-life of ${\mathrm{Mo}}^{99}$, 66.00±0.15 hr, has been determined.