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The animations below show etch pits made by
5.5 MeV alpha particles hitting the CR-39 surface at various angles.
It was made using images from a microscope camera and MorphBuster
2.2 |
(Each square is 36 microns wide)
 0 degrees
(normal incidence)
 15
degrees
 30
degrees
 45
degrees |
| When particles strike
CR-39 at different angles, the etch pits that are formed often
seem to have a tail when observed under a microscope. These 'tails'
are not actually part of the pit's opening at the surface, but
rather the bottom of the pit. This has an impact on what we see
as the 'top' view of the holes.
The image analysis software ImageJ, unaware of
this 'tail' effect, automatically fits an ellipse to the entire
image; this is shown by the green ellipse. The true surface opening
is represented by the orange ellipse and was measured by hand. |
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The extent to which this phenomenon affects what is
seen under the microscope depends on the particle's angle of incidence
and the track range. All of these etch pits are from 5.5 MeV alpha particles,
which have a range of ~34 um in CR-39.
View comparisons between the fit ellipse (with the
tail) and the true surface opening, with regard to: major
radius minor radius circularity
eccentricity |