RADIATION-DAMAGE IN NACL - THE ANNEALING BEHAVIOR OF HEAVILY DAMAGED KBF4 DOPED CRYSTALS

In this paper the annealing of Na colloids in heavily irradiated NaCl with damage levels up to 10 mol% is discussed. Recently the melting pr operties of Na colloids in heavily irradiated NaCl have been studied u sing differential scanning calorimetry. The observation of three endot hermal latent heat peaks, numbered 1, 2 and 3, as a function of the do se, has been reported. Here we discuss the annealing behaviour of heav ily irradiated crystals doped with KBF4, which show a large melting pe ak 3. The changes in the appearance of the latent heat peak provide us with information about the properties of the sodium colloids. The ann ealing of the colloids in two different temperature ranges is describe d. At moderate annealing temperatures between 160 and 210 degrees C th e peak shifts with annealing time to lower melting temperatures very r apidly. The shift of the peak is activated by an energy of 1-1.4 eV an d strongly depends on the initial amount of latent heat. At high tempe ratures between 250 and 320 degrees C a decrease of the latent heat is measured, due to the back reaction between Na colloids and molecular Cl-2. After continued annealing at high temperatures the melting behav iour becomes very anomalous. The melting peak splits into two peaks, t he main peak and a new, sharp one arising at 92 degrees C. After the s plitting of the peak the back reaction slows down significantly, activ ated by an energy of 1.2 +/- 0.3 eV. Both the moderate- and high-tempe rature annealing behaviour indicate that the processes are very local, with a short length scale of the order of 1 nm. This implies that the morphology of this type of colloid is highly irregular, with a dense and fine nanostructure.