Specific radioactivity of europium-152 in roof tiles exposed to atomic bomb radiation in Nagasaki

Specific radioactivities of residual europium (Eu)-152 were measured in six roof tile samples exposed to the Nagasaki atomic bomb at two locations. Th e ground distances of the two locations from the hypocenter are 1020 m and 1060 m. In order to obtain reliable data, Eu-enriched samples (from 207 to 855 mg) were prepared by separating Eu from each roof tile sample (from 1 t o 2 kg). For the major aliquot of the Eu-enriched sample, residual radioact ivity of Eu-152 was measured using a low-energy photon spectrometer. For th e minor aliquot of the Eu-enriched sample, Eu content was determined by neu tron activation analysis. Results of the specific radioactivity (Eu-152/Eu, Bq mg(-1)) corrected to the time of bombing were in a range from 0.080 to 0.446. Although the measured values showed some scattering, they are modera tely consistent with the calculated values by the DS86 methodology, i.e. th e average ratio of the calculated to measured values is 1.3 +/- 0.8.