Neutron dosimetry with cellulose nitrate films coated with lithium borate

Etching characteristics and thermal neutron sensitivity have been studied for two types of solid state track detectors: LR 115, type 2B stripping (LR-B) and CA 80-15 Type B (CA-B), prepared by Kodak-Pathe, France. The detectors were irradiated with neutrons in the Kyoto University Reactor or the Kinki University Reactor. The experiment proved that optimum etching times for the LR-B and CA-B film, respectively, were 45-60 and 30-60 minutes with 10% NaOH, 600C; and 90-120 and 15-30 minutes with 30% NaOH, 500C. Under these optimum etching conditions and times, the sensitivities for visual counting were found to be (2.1+-0.2)x10-3 and (1.9+-0.1)x10-3 for the LR-B and CA-B detectors, respectively. The spark counting sensitivity of the LR-B detector was found to be (1.9+-0.1)x10-4 under etching condition of 30% NaOH, 500C, and a time of 180 minutes. It was found that background spark conuts of the LR-B film were reduced remarkably by heat treatment at 1000C for 5hrs, which made it possible to detect a dose equivalent of 5x10-6 Sv (0.5 mrem) for thermal neutrons. (author)