Lessons learned from the TEPCO Fukushima No.1 NPS accident are discussed from the viewpoint of radiation protection in the situation of nuclear emergency. It became clear from the discussion that the protective measures should be practiced by taking into account the time profiles of the radiological disaster after the nuclear accident and that the land and coastal sea areas monitoring had to be practiced immediately after the nuclear accident and the communication methods to tell the public about the radiation information and the meaning of protective measures should be developed for mitigation of the sociological aspects of disaster impacts. And it was pointed out from the view point of practicing countermeasures that application of the reference levels, above which it was judged to be inappropriate to plan to allow exposure to occur, played an important role for practicing protective measures in an optimized way and that the quantities and units used for quantifying radiation exposure of individuals in terms of radiation doses have caused considerable communication problems. Finally, the occupational exposures and the public exposures that have been reported so far are shown, and it is concluded that there is no conclusive evidence on low dose exposures that would justify a modification of the radiation risk recommended by the International Commission on Radiological Protection.

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A new technique for estimating the neutron energy spectrum with CR-39 track detectors has been proposed for application to a singly pulsed neutron field where prevailing counters cannot operate properly. The CR-39 sample exposed to neutrons was intermittently etched, then the major and minor radii of respective etch pits were measured for each etching stage and the growth curve was obtained. The analysis method of growth curves was also designed, with which both the energy and the angle of recoil protons could be evaluated and converted into the energy of neutrons incident normally.The neutron irradiation experiments were carried out with the 46 MeV electron linear accelerator at the Research Reactor Institute, Kyoto University. It was confirmed from comparing with the reference spectrum measured by the neutron time-of-flight method that the present growth-curve method is useful for the estimation of the neutron energy distribution between about 0.3 and 2 MeV. Moreover, we have experimentally examined the unfolding method suggested by Matiullah and Durrani in order to extend the application of CR-39 detector to higher energies.

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