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- Author or Editor: S. Tagawa x
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Abstract
The molecular state of epoxy resins for cryogenic use has been studied in terms of positron lifetime measurement. The addition of plasticizer increased the free volume in the epoxy and hence the ductility of the epoxy at room temperature was increased. The fracture toughness at cryogenic temperatures, however, decreased. The increase of molecular weight between crosslinks decreased the free volume in the epoxy at room temperature and increased the fracture toughness slightly at cryogenic temperature. Based on the data the molecular state model desired for cryogenic application was proposed and the nano-sized silica dispersed epoxy was prepared by means of sol-gel method to follow the model. The cryogenic properties of the silica dispersed epoxy and the free volume evaluated by positron annihilation lifetime were also discussed.
Abstract
The concentrations of 7Be, 210Pb and 210Po of ca. 60 parts of a whole tree of Japanese cedar and of underlying litter and soil samples were determined for studying their transfer in a forest canopy. The results suggest that the mean residence times of 7Be and 210Pb in the forest canopy were ca. 20 and 900 days, respectively, and the dry deposition rate of 7Be on the forest canopy was about a half of the total deposition rate.
Abstract
The35S content in atmospheric deposition, aerosol and rain water was determined about every 10 days for a year with7Be,32P and some stable elements. Average35S concentrations were 110 mBq·m−2·d−1 for atmospheric deposition, 0.078 mBq·m−3 for aerosol in surface air and 45 mBq·l−1 for rain water. The ratios of7Be/35S were abnormally low, although most of32P/7Be showed the reasonable values corresponding to the residence times from 10 to 60 days. The excess35S suggests an external source of35S or/and a faster cycle of35S than that of7Be and32P.
Abstract
Activity concentrations of radionuclides,7Be,210Pb and210Po, in precipitation (rain, throughfall and stemflow), wood and soil were determined by using gamma-ray and alpha-ray spectrometry to estimate the migration behavior of these radionuclides in the forest canopy. The activity ratios between output and input precipitations for the forest canopy were 0.53 of7Be, 0.79 of210Pb and 1.5 of210Po for Pasania edulis forest. A dynamic model of the transport and fate of radionuclides in the forest ecosystem was constructed. Mean residence times of radionuclides were 56 days for7Be, 765 days for210Pb and 653 days for210Po for Pasania edulis forest.
Abstract
A new picosecond pulse radiolysis 
Twin LINAC System
has been constructed recently at Nuclear Engineering Research Laboratory at the University of Tokyo. The time resolution of the system is 20 ps and the system has a versatile capability for pulse radiolysis study. The outline of the facility is introduced. Some research carried out using the facility is presented. The examples are radiolysis of CCl4 and n-C21H44.
