The plastic known as CR39 was developed in 1933 and is now in widespread use as the material of which spectacle lenses are made. In 1978, physicists at Berkeley, California, reported that it was also an excellent detector of charged particles, which could be revealed by etching the plastic. While investigating the properties of CR39, the Bristol group taped a sample of the plastic to a window pane to observe the effect on the material of exposure to sunlight. When the sample was etched, it was found to have recorded the tracks of alphaparticles due to traces of uranium and thorium in the glass. The ease with which the small number of tracks could be recognised and measured showed CR39 to be an ideal material for lowlevel counting and, to pursue such research, the Track Analysis Group was formed. To obtain highquality material formulated specifically for track detection, the group experimented in producing CR39 at Bristol. To exploit the sales enquiries which followed their success, TASL was formed in 1983, and has now been producing TASTRAK, its version of CR39, routinely since 1985.

Address: Track Analysis Systems Ltd, Napier House, Meadow Grove, Shirehampton, Bristol, BS11 9PJ, U.K.
Telephone: 44 (0)117 938 1172
Website: http://www.tasl.co.uk/