Polystyrene is a main component of plastic scintillator, and it absorbs radon as well as liquid aromatic solvents. A new radon monitor was invented. The monitor detects radon which is distributed into plastic scintillator. A photomultiplier tube and plastic scintillator film were installed in a dark chamber, and radon water was introduced into the chamber. It was found that a scintillation spectrum of radon and daughters was observed. Then the radon concentration in water could be measured by use of plastic scintillator as an absorbent of radon. This method, APS: Absorptive Plastic Scintillation counting, is useful as a continuous monitor for radon in water.
The authors studied angular neutron fluence distributions in the neutron calibration field produced with a252Cf standard source. The neutron calibration field of Japan Nuclear Cycle Development Institute, Tokai Works, has utilized 50μg of252Cf doubly-encapsulated in a welded stainless steel (AEA Technology QSA, Xl capsule) . The neutron emission from source material itself is essentially isotropic, however, the source support structures, such as a source holder and an irradiation apparatus, significantly deviate neutron angular distributions from isotropy. To evaluate the departure from isotropy, the neutron angular fluence distributions for Xl capsule was calculated using the MCNP Monte Carlo code. Calculations were made of the fluence rate at various polar angle θ and azimuth angle α. Supplemental fluence distribution measurements were performed to verify computational results. As a result, an isotropy correction factor, Fs (θ=90°, α=0°), was evaluated to be 1.11±2% (k=2) . In addition, neutron energy spectral changes due to scattering was studied, and differences of spectrum-averaged dose conversion coefficients between values of this computation work and ISO recommendations were also discussed.
Concentrations of total U and Th in 82 Japanese agricultural soils (37 paddy field and 45 upland field soil samples) were determined by ICP-MS in order to estimate anthropogenic U contents. The geometric means of total U and Th in the paddy field soils were 2.75 mg kg-1and 5.56 mg kg-1, respectively, while those in the upland field soils were 2.43 mg kg-1and 5.17 mg kg-1, respectively. These values were within the range of reported values. The concentrations of Th and U in paddy field soils and upland field soils showed no differences between them, respectively. Concentration ratios of U/Th in paddy field and upland field soils were 0.53 and 0.49 on average, respectively, which were much higher than those in Japanese crust (0.28), non-agricultural fields (0.23) and river sediments (0.20) . These results imply that phosphatic fertilizers, which have high U concentrations, increased the total U concentrations of Japanese agricultural fields. Thus, using these U/Th ratios in non-agricultural areas, it is possible to calculate amounts of excess U due to the application of fertilizers. It was estimated that about 50% of total U in paddy field soils (range: 4-78%) and about 48% of total U in upland field soils (range: 4-74%) were originated from the phosphatic fertilizers.
Recently, FDG PET has become one of extremely important diagnostic imaging modalities. Initially, only several FDG PET examinations were performed per day at Nishidai Clinic Diagnostic Imaging Center. At present, however, approximately 40 FDG PET examinations have been performing per day using five positron cameras. Exposure dose to medical staffs increased owing to the increasing number of FDG PET examinations. To keep the exposure dose to the minimum, we designed the new measures as follows; reduction of hours, which require for a study results explanation just after study, introduction of an automatic injection system, and increase of the number of employees. In particular, the introduction of an automatic injection system, which is able to accurately measure radioactivity in a syringe, lowered the exposure dose of staffs in the injection room. The mean exposure doses of the staffs were 8.55μSv before and 1.30μSv after the introduction. The measures we designed seem helpful to reduce exposure dose of staffs in institutions associated with FDG PET examinations.
A virtual reality education and training system was developed for radiation workers. The function of the system is designed as a scenario which is programmed with a proprietary script language capable of defining motion of objects created by three-dimensional (3D) modeling software, user interaction, sounds and text strings displayed in the scene. Combining these functions enables the system to provide lectures and to judge the user's action. The system consists of the 3D model of the radiation facilities and three modes of scenarios (guidance, training and end-of-course examination) including the procedure to enter and exit, experiment, measurement, radioactive waste classification and accidents. By combining these modes, the trainee of education and training is possible to learn safety handling and how to act in the case of fire or earthquake.