Measurements of Neutron Fluence from the Hiroshima Atomic Bomb

Abstract

To estimate neutron doses from the Hiroshima atomic bomb (A-bomb), we measured residual radionuclides ³⁶Cl (half-life of 3.0 × 105 y) and ¹⁵²Eu (half-life of 13.3 y) in a tombstone near the hypocenter. Numerous samples were obtained from the surface and from inside the tombstone, and chlorine and europium were chemically isolated from them. The ratio ³⁶Cl/Cl was measured by accelerator mass spectrometry (ams) using the postaccelerator of the Munich Tandem laboratory. ¹⁵²Eu was determined with gamma-ray measurements in Hiroshima. The amount of isolated europium was determined by atomic absorption spectrometry. The attenuation curves from ³⁶Cl/Cl and ¹⁵²Eu/Eu furnished information about the neutron energy and the angular distributions near the hypocenter of the Hiroshima A-bomb.