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Nuclear Power Operation Safety and Environment Part 8

Tham khảo tài liệu 'nuclear power operation safety and environment part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Imaging of Radiation Accidentsand Radioactive Contamination Using Scintillators 199 Fig. 15. Streak camera image of the fluorescence from ZnO. This is a 50000-shot integrated signal excited by 56 nm. The vertical axis is wavelength nanometer and the horizontal axis is time nanosecond . The dominant fluorescence peak was centered at around 380 nm. Fig. 16. Temporal profiles of the ZnO fluorescence excited by a 51nm b 56nm and c 61 nm. The observed profiles can be fitted by double exponential decays described as I A1 exp -t t1 A2 exp -t T2 dotted line . The fitting parameters are A1 0.75 A2 0.25 T1 70ps and T2 222ps.The estimated instrumental function was plotted with a dot line in each graph. d Slit image dotted line and a calculated curve of a convolution of the slit image and a normal distribution function solid line . 200 Nuclear Power - Operation Safety and Environment Initially the response time of Fe-ion doped ZnO scintillator was evaluated using the third harmonics of a mode-locked Ti sapphire femtosecond laser at 290nm. The typical band-to-band ultraviolet fluorescence at 380nm was successfully observed with a decay time of 80ps. This is significantly faster compared with the previously reported 1-ns decay time for the 380-nm fluorescence of undoped ZnO. The 1x1cm2 0.5-mm thick double-side polished ZnO crystal was mounted in a vacuum chamber and the third harmonics of a neodymium-doped YAG Nd YAG laser was initially used as excitation for alignment purposes. The sample was illuminated from the backside in a counter propagation configuration with the beam path of the SCSS test accelerator as shown in Fig. 14. The SCSS test accelerator having 200-fs pulse duration 10-uJpulse energy and 20-Hz repetition rate was focused by an oblique mirror Mimura et al. 2008 . With a mirror focal length of 1m the spot size at the focus was about 20 pm. To minimize the risk of damage however the sample was placed 5 cm away from focus and the radius of the beam at this location