Improved Accuracy in the Measurement of 152Eu Induced by Atomic Bomb Neutrons in Nagasaki

152Eu activities induced by the atomic explosion in Nagasaki, have been experimentally estimated in two roof tiles in order to improve the accuracy of the former data about positions distant from the epicentre (at 1100 m) as the slant distance. Several aspects causing estimation errors have been discussed in more detail: i.e. influence of the natural background nuclides such as 210Bi, 210Pb, 212Bi and 138La, and half-life selection of 152Eu. As a result, the value of 152Eu/Eu (i.e. ratio of the 152Eu activity to total Eu) has been estimated to be 0.336 ± 0.032 (Sample A) and 0.491 ± 0.040 (Sample B) Bq.mg-1 as the values at the time of the bombing. In a comparison between the experimental values and the Dosimetry System 1986 (DS86) calculation, the ratio between DS86 calculations and the present work is estimated to be 0.40-0.58. More detailed discussion on the dose estimation of thermal neutrons might be needed for the improvement of the DS86 system. (author)