Response of CR‐39 to 2‐MeV microbeams of H, He, and Ne

CR‐39 (allyl diglycol carbonate), a plastic track detector, has been irradiated with 2‐MeV microbeams of H, He, and Ne in order to assess the usefulness of this detector for microbeam diagnostics. Optical microscopy, laser diffraction, and etching were used to examine the samples. A decrease in index of refraction, sufficient to make the radiation damage visible without etching, occurs for threshold doses between 5×104 and 5×105 particles/μm2 on beam spots 20 μm in diameter. Saturation of optical changes occurs at doses between 5×106 and 5×107 per μm 2. Diffraction intensity and optical activity were observed to develop with a time constant of several minutes after a short exposure. Below saturation, the developed diffraction intensity varies as the 1.5 power of dose. Relative diffraction intensities at a dose of 3×105/μm2 for H, He, and Ne are 1:14:93. The unetched detector is highly useful for i n s i t u observation of beam‐spot shape. Etching the detector can reveal many unexpected features.