SPECIFIC ACTIVITIES OF CO-60 AND EU-152 IN SAMPLES COLLECTED FROM THE ATOMIC-BOMB DOME IN HIROSHIMA

Neutron-induced activities Co-60 and Eu-152 have been measured for samples collected from the Atomic-Bomb Dome locating at 161 m from the hypocenter of the Hiroshima Bomb. Specific activities Co-60/Co and Eu-152/Eu at the time of the detonation have been determined as 10.0+/-1.0 Bq mg-1 (steel sample S4) and 80+/-9 Bq mg-1 (granite sample G1), respectively. Detailed measurements of Co-60 and Eu-152 activities for samples collected from various locations of the Dome show almost no directional dependence whether the sample faced to the epicenter or not, nor vertical height dependence between 17 m height and the ground level. In addition. Eu-152 was not detected in the sample collected from the basement. It has been shown that the present Co-60 activity value, the nearest steel one to the hypocenter, as well as other short distance data are systematically lower than the calculated values based on the neutron fluence of the DS86.