In broad terms, what type of microscope do I need for FTD work ?
FTD work is carried out at two magnifications : a low power objective is used to locate good candidate grains, and very high magnification is used to count tracks and measure their length.
Immersion oil is not used (except in work with zircon), as its refractive index is similar to that of both the mica and the apatite mineral grains, and it will cause any tracks to disappear !
FTD work is carried out in bright-field mode, making use of both transmitted and reflected light. The transmitted light mode results in good images of complete tracks, whereas the reflected light mode is used to accentuate the tracks' etch pit entrances.
In general terms, a microscope should have transmitted and reflected light sources with no less than 20 Watt output, high-quality (high numerical aperture, long working distance and flat field) dry objectives with 10x, 20x, 50x and 100x magnifying powers, a long-working distance condenser, and high-quality 10x eyepieces.
A so-called trinocular head, which incorporates a dual light path, allowing simultaneous or alternative use of the stereo eye-pieces and a top-mounted camera, is also required. To ensure camera attachment compatibility, the camera port on the microscope must be fitted with a so-called "C-mount" fitting. This is an industry-standard thread fitting which is incorporated in most cameras supplied for this purpose, and sometimes incorporates a reduction lens. The purpose of this lens is to make the on-screen images on the monitor the same as the view through the eyepieces.
One other essential item (but one which many microscopy laboratories may already own) is a high-quality stage micrometer. This is a standard microscope slide bearing a series of very accurately engraved lines at regular and known intervals. The stage micrometer is indispensable for calibration of the various system components. An eyepiece graticule, having a series of numbered and alphabetically indexed squares in a grid arrangement, is also a very useful adjunct. This item is fitted to one of the eyepieces and results in the grid being superimposed over the observed image. Traditionally, fission tracks were counted by FTD researcher, using these grids. They are usually fitted by us as a complimentary item, but are really no longer required, since almost all work is now done on-screen.
Other items of the system are dual large-format LCD monitors for simultaneous large-image viewing of grain and mica mounts. An optional item is a single, large and curved monitor for display of all information on a single screen, thus saving bench space (which is always at a premium).
For our latest software product (the automatic track counting module) to function properly, the following items are essential :
1. a high-quality motorised microscope, with stage and joystick
2. a high-quality digital camera
3. a very high performance PC
4. an anti-vibration table
5. a high-quality grinding and polishing setup
6. a facility for vacuum deposition of a reflective surface
(These items are explained separately in another FAQ)