Intercomparison study of Eu-152 and Cl-36 measurements

There were discrepancies between the data of the thermal neutron activation of Eu-152 and those calculated based on DS86. Comparing with DS86, the data were low near ground zero and high more than about 800 m ground range. After the Eu-152 measurement, Cl-36 data had been measured. At the longer distance the data of Cl-36 had better agreement with DS86. In the US and Japanese joint study we decided to start new intercomparison study using 16 granite samples (9 exposed and 7 control) to clarify such difference. These samples were cut into 5 pieces. One of the pieces was sent to the Japan Chemical Analysis Center and there dissolved to extract europium. The obtained samples are measured at Ogoya, Kanazawa University, in which Ge-detectors are installed in the old tunnel to reduce background. For the measurement of Cl-36 each of the three pieces were sent to the Tukuba University, Utah University and the Technical University of Munich and measured by AMS method. There is, in addition, a possibility such differences will occur in the process of the sample preparation. Therefore, we prepared mixtures of standard solutions of Eu and Cl and irradiated using the 252 Cf neutron source in Hiroshima University. Comparing with the new DS02 calculation, good agreements have been observed. Therefore we can clarify new results of 152 Eu and 36 Cl support the DS02 calculation within ground distance of 1100m. The specific activity of 36 Cl/35 Cl ratios divided by 152 Eu/151 Eu ratios are obtained and compared with the corresponding neutron capture cross section ratio of 35 Cl and 151 Eu (43.6 b and 5900 b, respectively). The ratio averaged over all measured samples is 0.87±0.03. According to the results of this study, the 152 Eu and 36 Cl data agree well with not only each other and also with the DS02 calculation