The CR-39 detectors were irradiated with three kinds of fast neutrons and etched in several alkaline solutions. Size distributions of etch-pits were obtained from analysis of micro- photographs. An automatic image analyzer was used to obtain the density of etch-pits. When etching conditions were kept at 30% KOH, 90°C and 1 h. the sensitivity was found to be 3.8xlO−4, 4.9 xlO−4 and 2.4 x10−4for fission, Am-Be and 14 MeV neutrons, respectively. From analysis of increasing rate of the sensitivity, it was found that the track density in CR-39 roughly corresponded to the density of elastic scattering with H, C and O in the case of Am-Be and 14 MeV neutrons, however, the track density was somewhat smaller than the elastic scattering density in the case of fission neutrons. The size of etch-pits increased with neutron energy. The etching time could be reduced to less than 1/10 as a result of a rising from 60 to 90°C. After due consideration of background counts, a dose equivalent of 0.2 mSv could be measured wit...
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