Early Intake of Radiocesium by Residents Living Near the Tepco Fukushima Dai-ichi Nuclear Power Plant After the Accident. Part 2: Relationship Between Internal Dose and Evacuation Behavior in Individuals

The Tokyo Electric Power Company's Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident exposed members of the public to radiation. This study analyses the relation between personal behavior data obtained from 112 out of 174 subjects who underwent whole-body measurements by the National Institute of Radiological Sciences (NIRS) during the period from 27 June to 28 July 2011 and their committed effective doses (CEDs) from Cs and Cs. The whereabouts of the 112 persons living in municipalities near the FDNPP (mainly, Namie town) on several days in March 2011 are graphed on maps. It was confirmed that most subjects started evacuation promptly and had left the 20-km-radius of the FDNPP by the end of 12 March. The individual CEDs were poorly correlated with the person's distances from the FDNPP at any day in March. Meanwhile, the percentage of persons remaining within the 20-km radius of the FDNPP was 100% at 16:00 on 12 March and 42.9% at 0:00 on 15 March for those with CEDs > 0.1 mSv, whereas the corresponding values were much lower for those with CEDs ≤ 0.1 mSv. This suggests that the time of evacuation would be one of the crucial factors for the early intake; however, more personal behavior data are needed to be analyzed to clarify the relevance to the individual internal dose

Rapid estimation of inhaled particle size for internal dose during nuclear emergency medicine

Information on particle size is one of the important factors for internal dose estimation at accidents with airborne radioactive materials. An autoradiography method has been investigated as a technique for the sizing of alpha-emitting particles. Concerning nuclear emergency medicine, the waiting time for dose estimation is limited. For determining the shortest estimation time, the exposure time of autoradiography was examined using 239PuO2 particles captured on HEPA filters. In this study, the effective counting efficiency of tracks produced by alphaparticles was evaluated to be 0.31 by a numerical simulation. The minimum exposure time for 239PuO2 with aerodynamic diameter of 5 µm was found to be only 10 min. When any star-like alpha particle track was not detected after 6 h of exposure, even if the sample had significant radioactivity, the aerodynamic diameterwas assumed to be less than 1 µm. When the radioactivity of 239PuO2 particles detected by autoradiography within 1 h was dominant of total activity, the aerodynamic diameter would be estimated to be over 5 µm. These results indicate that the precise dose estimation is useful for the decision of medical treatment

Development of radon sources with a high stability and a wide range

A solid 222Rn (radon) source using a fibrous and porous SiC ceramic disk was developed. The emission rate of radon emanated from the disk depended on the content of 226Ra and the sintering temperature. A 226Ra sulfate (226RaSO4) solution was dropped on a fibrous SiC ceramic disk (33 mmφ) of 1 mm in thickness, and sintered at 400 ◦C. The radon concentration from a disk containing 226Ra of 1.85 MBq was measured to be 38 kBq m−3 at a carrier airflow rate of 0.5 L min−1. By adjusting the 226Ra content or the sweep airflow rate, the radon concentrations were easily controlled over a wide range of over three orders of magnitude. The concentration was very stable for a long term. The compactness of the source disk made is easy for handling the source container and the shielding ofgamma radiation from 226Ra and its decay products. Such advantages in a radon generation system are desirable for experiments of high-level, large-scale radon exposure

Numerical Simulation on Dose Estimation from Nasal Swab Data at Nuclear Accident

A nasal swab sample, which is taken immediately after an inhalation accident of radioactive aerosols, shows provisional intake radioactivity. In the case of an alpha emitter, much time is needed to determine the intake radioactivity using bioassay. A nasal swab sample would be expected to be a determination method for early dose estimation. In this study, the most hazardous size to our health and how to estimate the exposure dose were considered from the viewpoint of emergency medicine. A computer code, LUDEP, was used to calculate the aerosol deposition in respiratory tract and the committed effective dose. Assuming that the radioactivity detected in a nasal swab sample was equal to the radioactivity deposited in the extrathoracic region 1 (ET1), the dose conversion factor (DCFnasal) was evaluated based on the relationship between the ET1 deposited radioactivity in Bq and the committed effective dose in mSv. The DCFnasal showed a clear dependency with the aerosol size. It was indicated that a reference aerosol size of 5 µm for occupational exposure in the ICRP publication was not always safe dose estimation for patients. In the case of insoluble plutonium-239, the maximum value of 2.6 mSv Bq-1 for DCFnasal was found at 0.02 µm in a heavy exercise level of an adult. Therefore, this indicated that the maximum value would make possible rapid dose estimation for nuclear emergency medicine

Characterisation of Nasal Swab Samples by Alpha Spectrometry

A positive nasal swab taken at a radiation emergency, when properly collected and analysed, is a good indication of a potential inhalation intake. It may be expected to be a useful method for early dose assessment in cases of accidental inhalation of an alpha emitter. To improve the first estimation of intake activity, the quality of a nasal swab measurement was experimentally investigated. Alpha spectrometry was used to examine the experimental nasal swab samples involved with a plutonium solution or particles. Also, a numerical simulation analysis on the alpha spectrum using advanced alpha-spectrometric simulation was made to characterise the experimental results. It was observed that the alpha energy spectrum had a quite different shape among samples, and it was characterised by the type of contaminant. This could be the second advantage of using alpha spectrometry in addition to nuclide identification. The absorption of alpha radiation within the experimental nasal swab sample was different between the types of contaminants. For a quantitative discussion, the absorption for a swab sample must be determined for each type of contaminant. This new finding could be very useful for first responders. A nasal swab sample measured using a alpha spectrometer will give more useful information during the first response of an emergency

Experimental Study of Sample Collection Efficiency in Nasal Swab Method

AOCRP-

Particle size measurement of radon decay products using MOUDI and GSA

6th International Conference on High Levels of Natural Radiation and Radon Area