Evidence for direct impact damage in metamict titanite CaTiSiO5.

We have measured the dose dependence of the degree of amorphization of titanite, CaTiSiO(5). Titanite is an often metamict mineral which has been considered as a matrix for the encapsulation of radiogenic waste, such as Pu. The amorphous fraction p of geologically irradiated samples (ages between 0.3 and 1 Ga) follows p = 1 - exp(-B(a)D) where D is the total dose and the characteristic amorphization mass is B(a) = 2.7(3) × 10(-19) g. Amorphization follows the direct impact mechanism where each α-decay leads to a recoil of the radiogenic atoms (mostly Th and U), which then, in turn, displaces some 5000 atoms of the titanite matrix. The amorphization behaviour is almost identical with that of zircon, ZrSiO(4), which has a similar molecular mass. While the recrystallization mechanism and elastic behaviour of the two minerals are very different, we do not find significant differences for the amorphization mechanism. Our samples have undergone little reheating over their geological history, since heating over 800 K would lead to rapid recrystallization for which we have found no evidence.

Thermal diffusivity by laser intensity modulation method (LIMM-TD): a novel technique for the determination of thermal diffusivities and conductivities and its application to porous PZT and silica samples.

A modification of a technique for the measurement of the thermal diffusivity of thin solid materials is presented. The technique is called Thermal Diffusivity by Laser Intensity Modulation Method (LIMM-TD). It is based on the measurement of the phase retardation of a thermal wave passing through the test material by means of a lead-zirconate-titanate ceramic (PZT) pyroelectric detector. It is not necessary to know either the pyroelectric coefficient of the detector or the intensity of the laser beam. The method was tested on quartz samples to verify its accuracy. It was then applied to the study of several sets of ceramic samples with porosities of 20, 25, and 30%. One sample set was poled and the pores were partially filled with the fluid used during poling. A second set was not poled. The poled porous samples had thermal conductivities intermediate between that of a commercial dense sample and those of unpoled materials. Thermal diffusivities and conductivities were also measured on micron-thickness porous silica samples. The experimental results were compared with calculations using several composite mixing theories.