The energy release associated with the recovery peak occurring between 600 and 700 deg K in neutron-irradiated copper was measured utilizing a new technique, that of nuclear heating. Following a bombardment at 40 deg C of 1.7 x lO/sup 20/ fast neutrons of a l/E distribution which raised the critical shear stress to 12.8 kg/mm/sup 2/ at 4.2"K (5.2 kg/mm/sup 2/ at 300 deg K), a release of 7.7 cal/mole was measured. Using this measured value of the energy release it is possible to estimate the number of defects annihilated if it is assumed that the annealing is the result of the migration and subsequent annihilation of a single defect. In this way the number of interstitials, vacancies, interstitial- vacancy pairs, and dislocation lines required to account for the measured energy release were estimated. The values were, respectively, 5 x lO/sup 19/ per mole, 2 x lO/sup 20/ per mole, 4 x lO/sup 19/ per mole, and 1 x lO/sup 12/ cm per mole. (auth)