This is a plastic chip from a radon testing device called an Alpha track detector.
It was exposed to the EPA Action level of 4 pCi/l of radon for 3 months.
The pitted areas caused by the breakdown of the Alpha particle are clearly
visible when viewed under a microscope at only 100 times magnification.
Although the above alpha track detector is plastic, some of the original
alpha tracks were made of glass, the alpha particle had the same effect on glass
as it did on this plastic.