Dismantling work of cyclotron of Tohoku University and measurement of induced radioisotopes

This paper described the outline of dismantling work of Tohoku University AVF cyclotron and measurement of induced radioisotopes in the accelerator and facility. Operation of the cyclotron started from 1977 and ceased in 1998. The dismantling work was only for the accelerator unit and did not involve one for the beam transfer system. The work required 3 (average) workers/day and 42 days in total. The average external dose was 272 μSv with negligible internal exposure. The beam system was stocked for its re-utilization. For measurement of dose and radioactivity, the ionization chamber survey-meter Aloka ICS-301, NaI(Tl) scintillation survey-meter Aloka PCS-161 and PureGe detector CANBERA GC3010-7600SL were used. The part with the highest dose was found the deflector, No. 1 of which had the surface dose equivalent to 35 mSv/h and No. 2, 4 mSv/h. 65Zn and 60Co were detected. Dee and main probe also had the high radioactivity. In the magnet, 60Co, 59Fe and 54Mn were contained. On the surface of drum where the waste was disposed, the highest dose was 5 mSv/h. The ambient dose in the facility was 0.4 μSv/h at the highest, which was mainly derived from 60Co and 152Eu. The latter, possessing more than twice longer half life than 60Co, would be a problem. (K.H.)