Skull counting in late stages after internal contamination by actinides.

Monitoring preparation for internal contamination with actinides (e.g. Pu and Am) is required to assess internal doses at nuclear fuel cycle-related facilities. In this paper, the authors focus on skull counting in case of single-incident inhalation of (241)Am and propose an effective procedure for skull counting with an existing system, taking into account the biokinetic behaviour of (241)Am in the human body. The predicted response of the system to skull counting under a certain counting geometry was found to be only ∼1.0 × 10(-5) cps Bq(-1) 1y after intake. However, this disadvantage could be remedied by repeated measurements of the skull during the late stage of the intake due to the predicted response reaching a plateau at about the 1000th day after exposure and exceeding that in the lung counting. Further studies are needed for the development of a new detection system with higher sensitivity to perform reliable internal dose estimations based on direct measurements.

Calibration of KVp meter used in quality control tests of diagnostic X-ray units.

In diagnostic radiology, the tube voltage [peak kilovoltage (kV(p))] is one of the most important parameter affecting both radiation exposure and image contrast. So, an accurate kV(p) meter is necessary to control kV(p) in the medical radiography practice with the overall uncertainty less than ± 5 % according to IEC 61676. Therefore, both invasive and non-invasive calibration methods of kV(p) meter were established and applied to different kinds of commercial quality control instruments for diagnostic radiology. Calibration of kV(p) meter by the invasive method is the most accurate (with uncertainty of 1.67 %, k=2); however, the non-invasive method also provides good results (with uncertainty of 3.12 %, k=2). Due to their detailed design, the commercial kV(p) meters have various responses with X-ray beam, so the working regime of a particular device type must be appropriately selected with a specific X-ray machine used for calibration of kV(p) meter.

Dose evaluation from multiple detector outputs using convex optimisation.

A dose evaluation using multiple radiation detectors can be improved by the convex optimisation method. It enables flexible dose evaluation corresponding to the actual radiation energy spectrum. An application to the neutron ambient dose equivalent evaluation is investigated using a mixed-gas proportional counter. The convex derives the certain neutron ambient dose with certain width corresponding to the true neutron energy spectrum. The range of the evaluated dose is comparable to the error of conventional neutron dose measurement equipments. An application to the neutron individual dose equivalent measurement is also investigated. Convexes of particular dosemeter combinations evaluate the individual dose equivalent better than the dose evaluation of a single dosemeter. The combinations of dosemeters with high orthogonality of their response characteristics tend to provide a good suitability for dose evaluation.

Management of cosmic radiation exposure for aircraft crew in Japan.

The International Commission on Radiological Protection has recommended that cosmic radiation exposure of crew in commercial jet aircraft be considered as occupational exposure. In Japan, the Radiation Council of the government has established a guideline that requests domestic airlines to voluntarily keep the effective dose of cosmic radiation for aircraft crew below 5 mSv y(-1). The guideline also gives some advice and policies regarding the method of cosmic radiation dosimetry, the necessity of explanation and education about this issue, a way to view and record dose data, and the necessity of medical examination for crew. The National Institute of Radiological Sciences helps the airlines to follow the guideline, particularly for the determination of aviation route doses by numerical simulation. The calculation is performed using an original, easy-to-use program package called 'JISCARD EX' coupled with a PHITS-based analytical model and a GEANT4-based particle tracing code. The new radiation weighting factors recommended in 2007 are employed for effective dose determination. The annual individual doses of aircraft crew were estimated using this program.

Benchmarking of activation reaction distribution in an intermediate energy neutron field.

Neutron-induced reaction rate depth profiles inside concrete shield irradiated by intermediate energy neutron were calculated using a Monte-Carlo code and compared with an experiment. An irradiation field of intermediate neutron produced in the forward direction from a thick (stopping length) target bombarded by 400 MeV nucleon(-1) carbon ions was arranged at the heavy ion medical accelerator in Chiba. Ordinary concrete shield of 90 cm thickness was installed 50 cm downstream the iron target. Activation detectors of aluminum, gold and gold covered with cadmium were inserted at various depths. Irradiated samples were extracted after exposure and gamma-ray spectrometry was performed for each sample. Comparison of experimental and calculated shows good agreement for both low- and high-energy neutron-induced reaction except for (27)Al(n,X)(24)Na reaction at the surface.

Discussion on framework of radon management strategy in various environments.

Activities on radon management strategy of international organisations (International Atomic Energy Agency, International Commission on Radiation Protection, etc.) should be carefully and continuously traced to discuss how to control radon in various environments, for example, dwellings, workplace, underground, caves, mines, hot springs, disposal facilities and so on. It is more reasonable in parallel to set radon reference level by effective dose criteria of Sv y(-1) as well as by radon concentration in air of Bq m(-3). How to investigate radon concentration in each environment, and how to make decisions on needed action for radiation protection from natural radon,--these should be discussed for each environmental situation on a case-by-case basis. International discussion as well as domestic discussion is continuously needed, not only among the radon specialists and regulators, but also including stakeholders who are the main users of regulation and guidance.

Temperature calibration formula for activated charcoal radon collectors.

Radon adsorption by activated charcoal collectors such as PicoRad radon detectors is known to be largely affected by temperature and relative humidity. Quantitative models are, however, still needed for accurate radon estimation in a variable environment. Here we introduce a temperature calibration formula based on the gas adsorption theory to evaluate the radon concentration in air from the average temperature, collection time, and liquid scintillation count rate. On the basis of calibration experiments done by using the 25 m³ radon chamber available at the National Institute of Radiological Sciences in Japan, we found that the radon adsorption efficiency may vary up to a factor of two for temperatures typical of indoor conditions. We expect our results to be useful for establishing standardized protocols for optimized radon assessment in dwellings and workplaces.

Relationship between variations of (7)Be, (210)Pb and (212)Pb concentrations and sub-regional atmospheric transport: Simultaneous observation at distant locations.

In order to investigate the applicability of (212)Pb as a tracer for atmospheric transport in the sub-regional scale (few hundred kilometers in horizontal direction and up to approximately 1km by height), we measured the air concentrations of the short-lived radionuclide (212)Pb along with the long-lived (7)Be and (210)Pb near the ground surface. For this purpose, simultaneous observations were continued for several days at three locations: a reference point representative for standard land surface atmosphere conditions, a second location at an altitude 650 m near the reference point, and on a solitary island approximately 180 km from the reference point. Measurements of radioactivity in aerosol particle samples collected at intervals of 2-3h with a high-volume air sampler were performed by extremely low background gamma-ray spectrometry with the use of Ge detectors located at the Ogoya Underground Laboratory. Concentration of (7)Be or (210)Pb and their variation patterns was found to be similar among the three points during the whole observation period except for moment of the passage of a cold front. The results indicate that distributions of concentrations of the long-lived nuclides were uniform in this range. On the other hand, concentration levels and the variation patterns of the short-lived (212)Pb differed greatly from one location to another, reflecting differences in geographical location and altitude of the observation points. Additionally, there were certain indications that observed concentration of (212)Pb contained two components: an autogenous component from sources nearby and a heterogenous one from faraway sources carried by atmospheric horizontal transport. Results of this study provide experimental proof that (212)Pb can be used as a tracer of sub-regional atmospheric transport.

Applicability of convex hull in multiple detector response space for neutron dose measurements.

A novel neutron dose measurement method that flexibly responds to variations in the neutron field is being developed by Japan Atomic Energy Agency. This is an implementation of the multi-detector method (first introduced in 1960s) for neutron dose evaluation using a convex hull in the response space defined for multiple detectors. The convex hull provides a range of possible neutron dose corresponding to the incident neutron spectrum. Feasibility of the method was studied using a simulated response of mixed gas proportional counter. Monochromatic neutrons are shown to be fundamentally suitable for mapping the convex. The convex hull can be further reduced taking into consideration a priori information about physically possible incident neutron spectra, for example, theoretically derived moderated neutron spectra originated from a fission neutron source.

Development of a technique for the measurement of the radon exhalation rate using an activated charcoal collector.

A simple system to evaluate the 222Rn (radon) exhalation rate from soil has been improved. A sampling cuvette of 2.1 L is placed so that it covers the targeted ground soil, and radon emanating from the soil accumulates within the cuvette for 24 h. Its internal radon concentration is measured by the combination of an activated charcoal (PICO-RAD) and a liquid scintillation counting system. This study shows variations of the conversion factor (CF: unit Bq m(-3)/cpm) of PICO-RAD. The range of CF due to temperature (10-30 degrees C) was between -21% and +69%, and this due to humidity (30-90%) was between 0% and -15%. Humidity and radon concentration in the cuvette covering soil tended to saturate in a few hours. The above information was used to correct the CF for the evaluation. The improved system shows high reliability and can be easily applied to natural environments.

Application of activated charcoal radon collectors in high humidity environments.

Most commercially based activated charcoal radon collectors were designed for use in indoor environments. However, at present, they are often used for research in radon surveys in unique environments, such as in the bathrooms, underground areas, mines, caves and tunnels. In these environments, the relative humidity would be around 100%, and a change in the sensitivity of cpm(Bq m(-3))(-1)(radon) would occur. For this study, the reduction in the sensitivity of activated charcoal radon collector due to environmental humidity was investigated, and the data correction was discussed. Here, ST-100 (Pico-Rad) was selected as an example of a familiar activated charcoal radon collector. According to our performance test, the humidity of 90% (20 degrees C) resulted in a 15% reduction of the sensitivity for 24 h collection. The ST-100 user should discuss the necessity of data correction by comparing the change of sensitivity with other levels of estimation errors.