Measurement of stored energy of KBr after X-irradiation at low temperature

The release of stored energy of X-irradiated KBr measured between 10 and 50K. A very sensitive heat flow calorimeter is described, which allows the detection of energy release rates as small as 0.5% of the heat capacity of the sample. The observed annealing stages of stored energy are compared with lattice parameter, length change, and optical absorption measurements from similar annealing experiments. The energy release can be identified as due to recombination of Frenkel pairs. The stored energy per Frenkel pair was obtained in KBr by combined measurements of the energy release and the change of optical absorption while warming up an irradiated crystal. For the alpha +I Frenkel pair a value of (4.0+or-0.8) eV was found. For the recombination of an F+H Frenkel pair an energy release of (2.7+or-0.6) eV was obtained.