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. The 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 to 2 kg). For the major aliquot of the Eu-enriched sample, residual radioactivity of Eu-152 was measured using a low-energy photon spectrometer. For the minor aliquot of the Eu-enriched sample, Eu content was determined by neutron 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 moderately consistent with the calculated values by the DS86 methodology, i.e. the average ratio of the calculated to measured values is 1.3 +/- 0.8.