The authors calculated anisotropy factors for241Am-Be neutron sources used for calibration of neutronmeasuring devices for radiation protection purpose. In this calculation, we created a calculation model composed of following three steps: (1) calculation of α-particle spectrum at the surface of spherical cluster of AmO2, (2) calculation of neutron yield in a thick beryllium target and of neutron spectrum produced by9Be (α, n) reactions ; and (3) calculation of angular fluence distribution of neutrons emerging from two different encapsulation types of241Am-Be neutron sources. This computation was made by combining an in-house code using the9Be (α, n) cross section data library (JENDL/AN-2005) and the Monte Carlo code MCNP-4C. As a result, anisotropy factors in the direction perpendicular to the source capsule axis were evaluated to be 1.030 and 1.039 for241Am-Be in a standard Amersham X3 capsule and X4 capsule, respectively. These values are in reasonable close agreement with the published experimental data. If the support structures are included in the simulation, the anisotropy factors for these neutron sources increase by about 10%.
Since ionizing radiation is used for sterilizing or lowering the microbial content of foods as a means of reducing food losses and securing food safety, the development of versatile detection methods of irradiated foods is necessary for appropriate management. In an effort to distinguish between irradiated and non-irradiated food, a method based on the detection of oxidative DNA base damage using the chemiluminescence enzyme-linked immunosorbent assay (ELISA) with anti-8-hydroxy-2'-deoxyguanosine antibody was developed. In the course of optimizing the reaction conditions for the ELISA, a 30-mer synthetic oligonucleotide containing 8-hydroxyguanine (8-oxoG) was used. Under the optimized conditions, the correlation between chemiluminescence intensity and 8-oxoG content in oligonucleotides was obtained. It was shown that this chemiluminescence ELISA method could be applied to chicken, beef and pork that were irradiated with over 3 kGy. Twenty milligrams of a loaf of meat was sufficient to distinguish between irradiated and non-irradiated meat by this method.
From the viewpoint of radiological dose assessment, 137Cs is one of the most important radionuclides due to its long half life (30 y) . In this work, sorption behavior of137Cs in Japanese paddy field soils was investigated, taking into account effects of chemical properties. Soil-soil solution distribution coefficients (KdS) which are defined as the relation between an adsorbed radionuclide concentration and that present in the solution were measured for 30 paddy field soil samples collected throughout Japan. These measurements were carried out using the batch sorption test. Then, sequential extraction methods were carried out to determine the ratio of137Cs fixed on soil. In addition, soil properties, such as pH, cation exchange capacity (CEC) and total carbon, total nitrogen and clay contents were measured as well. X-ray diffraction analysis was carried out to identify the clay minerals in soil samples. In particular, content of illite which can sorb Cs strongly was determined as a relative amount for all soil samples. Kdvalues ranged from 269-16 637 L/kg (geometric mean =2286 L/kg) . A correlation was observed between the Kdvalues and clay content with a Spearman rank correlation coefficient (Rc) of 0.55 (p<0.005) . On the other hand, the ratio of137Cs fixed in soil had good correlation with relative illite content (Rc=0.68, p<0.001) . Therefore, illite content could be more important than clay content for estimation of the amount of137Cs fixed on soil.