Michel Rebetez

ABSTRACT The, track annealing phenomenon, which occurs in a heated mineral containing uranium like apatite, is analysed using the transmitted electron microscopy (TEM) associated to the platinium shadowed carbon replica method. The diameters of 86Kr (1,66 MeV/nucleon) ion tracks induced normally to the observation plane are measured during an etching stage with a very low concentrated etchant (HNO3 1%). The distribution of track diameters in a sample, and its variation following the annealing amount the apatite knew, lead us to agree with the track registration model which let appear more than one microscopic defect structure (Dartyge et al., 1981). This model cannot be observed with only unannealed etched tracks, but is clearly highlighted by the thermal annealing of nuclear tracks in this mineral. The opening track profile is analysed as a determination of the etching speed variation versus the distance to the ion trajectory. The variation is shown to be dependent on the cristallogaphy of the apatite. The different etching speeds, relative to the orientation with the c-axis of the apatite, influence the track shape for long etching times. The etched pit figure is not symetrical, and present in the c-axis direction a much more width opening than the etched track diameter. Finaly, the lateral track shape and the etched pit are supposed to be sensitive to the etchant strength.

ABSTRACT Samples of monosilicated sintered fluorapatite (Ca9Nd(PO4)5(SiO4)F2, britholite) and full-phosphated Durango fluorapatite were irradiated using different heavy ions with incident energies in the range of several hundred MeV, corresponding to the electronic stopping power regime. The induced damage was characterized by means of X-ray diffraction for the monosilicated fluorapatites and Rutherford backscattering spectrometry associated with channeling technique (CRBS) for the Durango fluorapatites. Characterizing the amorphization of the monosilicated fluorapatites revealed two main features. First, the evolution of the damaged fraction with the ion fluence and the ion species shows that amorphization is mainly dependent on the electronic energy loss (Se) value. Second, we suggest that a percolation of defects only occurs when Se is above a threshold near 5 keV nm−1. This can be related to the limit of a fragmentation zone defined from microscopic observations. We have quantified damage in monosilicated fluorapatites by calculating amorphization effective radii (Re). By plotting these results versus Se, we found that they are in good agreement with those obtained from the irradiated single crystals of Durango fluorapatite.

ABSTRACT Theoretical models which confirm experimental distributions of lengths of both surface and confined tracks must be devised in order to promote the development of fission track applications in minerals. In a previous study, using a mathematical model, the characteristics of surface tracks were calculated.1 The algorithm has now been extended to confined track length distributions (TINT and TINC). Results show that distributions are not as simple as researchers had previously supposed. This method requires strict experimental conditions since a high background noise is associated with the characteristics of etching (bulk etching rate over track etching rate and etching duration). Ideal conditions are determined to observe a narrow peak with a low background noise.

ABSTRACT For convenient utilization of track detectors, results must be obtained quickly, so automatic processes are usually employed. To this end two techniques are investigated : spark counter and quantimet system. The first one is appropriate for low densities (below 4000 tracks/cm2) ; for densities between 4000 tracks/cm2 and 2.2 105 tracks/cm2 counting is performed with a Cambridge Quantimet 720 ; for higher densities, two different methods are described which take into account the overlapping of tracks.

ABSTRACT A new approach to the problem of investigation of charge and energy spectra of ultra heavy Galactic cosmic ray nuclei, based on fossil track study of extraterrestrial olivine crystals has been developed. The results of an investigation of ultra heavy Galactic cosmic ray nuclei (Z=50-92) in meteoritic olivine crystals are presented. The technique was based on calibration of olivine crystals with accelerated Xe, Au, Pb and U ions and well-controlled partial annealing of "fresh" and "fossil" tracks. It allows us to determine the charge spectra and abundances of cosmic ray nuclei based on fossil track length study in meteoritic and Moon crystals. The comparative studies of the spectra of "fossil' tracks and tracks due to 208Pb and 238U nuclei have shown that the group of 210 micrometers "fossil" tracks, first observed in 1980 at JINR is due to Th-U nuclei-products of recent r-process nucleosynthesis in our Galaxy. The method in principle allows one to resolve Pt-Pb peaks in fossil tracks, to establish the upper limit of the abundance of Z>110 nuclei in the Galactic cosmic rays at the level < or = 10(-3) to the abundance of actinide nuclei and to get information on the history of Z>50 cosmic ray nuclei in time interval up to 220 M.Y.

A microsonoreactor, specially designed to carry out electrochemical tests in a room-temperature ionic liquid medium (RTIL), was studied. The cell, based on a particular design consisting of off-setting the ultrasonic probe out of the reaction volume, was characterized by several methods such as calorimetry, dosimetry and mass transfer measurements. The main result concerns the specific behaviour of the ionic liquid under ultrasonic irradiation. For example, the mass-transfer enhancement is particularly high, characterized by an average Sherwood number of 6500 while the value obtained with an electrode rotating at 4500 rpm is only 1200.