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Following the angular distribution measurement of bremsstrahlung, we measured the angular distribution of photoneutrons between 0 and 120 degrees from copper and tungsten targets bombarded by 18, 28, and 38 MeV electrons at the electron linac of Hokkaido University. The activation detectors and neutron dosimeters were applied to the measurement. The measured results were compared with the results calculated with the Monte Carlo code MCNP5 to verify the calculated results. The calculated results of both the reaction and ambient dose equivalent rates were in good agreement with the measured ones between 20 and 120 degrees in the cases of 28 and 38 MeV electrons, but the calculation underestimated the measured data by a factor of 1.5 to 2.5 for 18 MeV electrons. A large disagreement was observed at small forward angles of around 0 degrees. It was clarified that this disagreement was due to the contributions of photonuclear reactions in the detectors and dosimeters themselves, and of (e,n) reactions in the target.

Large microscopic inclusions from 20 to 100 μm in diameter have recently been paid attention from a viewpoint of fatigue strength of steel products. As the inclusion detection capability, or probability, is practically limited by a conventional optical microscopy, however, the evaluation of the distribution of these inclusions used to be feasible only by extraction method such as acid-solution procedure. It has been found that ultrasonic testing with 50 to 12S MHz frequency, focus-type transducers is suitable to evaluate the inclusions where the echo intensity is proportional to inclusion diameter. This paper will describe recent inclusion evaluation procedures and, as a main body, the results of the application of the new ultrasonic testing system. Included are: The relationship between oxygen content in steel and maximum inclusion diameter in steel predicted by statistics of extreme value with the aid of microscopic image analysis, and The inclusion diameter distribution measured directly by the ultrasonic testing