Annealing of radiation damaged monazite

Differential scanning calorimetry measurements have been carried out on a specimen of monazite mineral, (Ce,La)PO4 after irradiation by 3 MeV Ar+ ions with fluences up to 20 ions nm-2. Specimens were annealed before irradiation to remove any radiation damage effects in the natural mineral. The degree of damage due to irradiation is assessed by measurement of the principal x-ray diffraction lines. Upon scanning the temperature to 750K, the annealing process is completed and the x-ray diffraction lines return to their original intensities. The activation energy for annealing is found to be 3.25 +- 0.4 eV and the rate constant for the process may be expressed as K/sub T/ = 4 x 1011 exp(-3.25 eV/k/sub B/T) s-1. The stored energy increases with increase in fluence but seems to saturate at a maximum value of about 8 cal g-1. The generally crystalline condition of naturally occurring mineral monazite is accounted for by the equilibrium between the damaging process due to radioactive impurities and the natural annealing at ambient temperatures. This equilibrium is heavily in favor of the annealing process