SLM confocal microscopy: an improved way of viewing fission tracks

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Abstract
Fission track analysis as a geochronological, and more recently a palaeothermal technique is a lengthy process, often complicated by problems of track recognition. While recent developments in computerized track counting systems should lead to improved efficiency, they still rely on transmitted light as the principal means of track detection, and do not deal with the problem of track recognition. We present here some preliminary results using confocal scanning laser microscopy (SLM) of a study of fission tracks in apatite from the Fish Canyon tuff, and show how the technique can lead to improvements in track identification. Defects formed in solids as a result of the spontaneous fission of the heavy nuclide 238 U are called fission tracks (Silk & Barnes 1959) and are found in a number of geologically important uranium-bearing phases including micas, titanite, zircon and apatite. The analysis of fission tracks has, until quite recently, been primarily concerned with age determination where it has proved useful in both the earth sciences and archaeology ( Fleischer et al. 1975 ). More recently, the recognition that at elevated temperatures the tracks become unstable and ultimately anneal ( Naeser 1981 ; Green et al. 1986 ), has led to the study of track lengths, especially in apatite, where track annealing occurs over the hydrocarbon maturation window temperature. ( Gleadow et al. 1983 ). Although the study of fission track length data promises to be a useful tool in evaluating palaeotemperatures in some sedimentary basins ( Gleadow et al. 1983 , 1986 ; Green 1989 ), the measurements involved in both track counting and