Rapid detection of plutonium contamination with and without uranium contamination in wounds by x-ray fluorescence.

In the event of an accident at a nuclear fuel handling facility, the wounds of affected workers may be contaminated with plutonium. The current approach for identifying plutonium contamination is by detecting α-particles in the blood stream. However, the applicability of this approach is impeded due to the α-particles being easily shielded by the bodily fluid components. In this study, we investigate a contamination testing method for such cases that involves the collection of blood with a small piece of filter paper, sealing the sample with thin films, and performing x-ray fluorescence analysis. Our previous study on collecting uranium-contaminated blood with filter paper and performing x-ray fluorescence analysis revealed that the effects arising from blood components could be completely removed by peak fitting, and thus water instead of blood was used as a solvent here. Samples containing various amounts of plutonium as well as samples with 150 Bq of plutonium and uranium were prepared with a mass ratio of 0 to 500 times greater than that of plutonium. x-ray fluorescence measurements showed a high linearity and reproducibility of the Pu Lα peak intensity and plutonium radioactivity, and it was clarified that the signal intensity of the Pu Lα peak did not depend on the amount of coexisting uranium. This method will allow for the simple and rapid assessment of plutonium contamination in wounds.

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.

Quantification of damage due to low-dose radiation exposure in mice: construction and application of a biodosimetric model using mRNA indicators in circulating white blood cells.

Biodosimetry, the measurement of radiation damage in a biologic sample, is a reliable tool for increasing the accuracy of dose estimation. Although established chromosome analyses are suitable for estimating the absorbed dose after high-dose irradiation, biodosimetric methodology to measure damage following low-dose exposure is underdeveloped. RNA analysis of circulating blood containing radiation-sensitive cells is a candidate biodosimetry method. Here we quantified RNA from a small amount of blood isolated from mice following low-dose body irradiation (<0.5 Gy) aimed at developing biodosimetric tools for situations that are difficult to study in humans. By focusing on radiation-sensitive undifferentiated cells in the blood based on Myc RNA expression, we quantified the relative levels of RNA for DNA damage-induced (DDI) genes, such as Bax, Bbc3 and Cdkn1a. The RNA ratios of DDI genes/Myc in the blood increased in a dose-dependent manner 4 h after whole-body irradiation at doses ranging from 0.1 to 0.5 Gy (air-kerma) of X-rays, regardless of whether the mice were in an active or resting state. The RNA ratios were significantly increased after 0.014 Gy (air-kerma) of single X-ray irradiation. The RNA ratios were directly proportional to the absorbed doses in water ranging from 0.1 to 0.5 Gy, based on gamma-irradiation from (137)Cs. Four hours after continuous irradiation with gamma-rays or by internal contamination with a beta-emitter, the increased RNA ratios resembled those following single irradiation. These findings indicate that the RNA status can be utilized as a biodosimetric tool to estimate low-dose radiation when focusing on undifferentiated cells in blood.

Intake ratio of 131I to 137Cs derived from thyroid and whole-body doses to Fukushima residents.

This study deals with the intake ratio of (131)I to (137)Cs that allows for the utilisation of late whole-body measurements to reconstruct the internal thyroid doses to Fukushima residents. The ratio was derived from the thyroid dose distribution of children and the effective dose distribution of adults based on the assumption that various age groups of persons inhaled the two nuclides at the same activity ratio and at around the same time, while taking into account age-dependent ventilation rates. The two dose distributions were obtained from residents of Iitate village and Kawamata town, located northwest of Fukushima Daiichi nuclear power plant (FDNPP). As a result, the intake ratios for the residents were 2-3, which was much smaller than the activity ratio observed in air sampling. A main reason for this discrepancy presumably lies in the relatively smaller thyroid uptake for iodine in the Japanese subjects than that in the reference persons on whom the biokinetic model promulgated by International Commission on Radiological Protection is based. The actual intake ratio of the two nuclides is believed to have been higher south of the FDNPP; however, this would depend on which of three significant plume events dominantly contributed to the intake for individuals. Further studies are needed to clarify this issue as a part of the reconstruction of early internal doses related to the FDNPP accident.

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 PuO2 particles captured on HEPA filters. In this study, the effective counting efficiency of tracks produced by alpha particles was evaluated to be 0.31 by a numerical simulation. The minimum exposure time for PuO2 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 diameter was assumed to be less than 1 µm. When the radioactivity of PuO2 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.

Contamination control by a greenhouse for emergency medical treatment of the contaminated patient.

In emergency medical treatment of patients contaminated with radioactivity, air contamination control is very important to prevent the secondary contamination of medical staff. In order to optimize design of a greenhouse, a numerical analysis was made by using the Flow Designer software. As a scenario of air contamination, the breathing air of the patient was assumed to be highly contaminated with radioactive gaseous or particulate matter. It was found that air contamination strongly depended on the characteristics of the contaminants. The contamination map of the coarse aerosols with low diffusivity was quite different from those of the fine aerosols and gas. If the setting conditions of air-flow rate of the ventilation and the exhausting position were optimized, secondary contamination of the medical staff standing by the patient is prevented securely by a greenhouse.

Identification of mouse mutant cells exhibiting the plastic mutant phenotype.

The initial processes involved in radiation carcinogenesis have not been clearly elucidated. We isolated mouse mutant cells exhibiting plasticity in their mutation phenotypes. These mutant cells were originally isolated from an irradiated cell population as 6-thioguanine resistant (6TGR) mutants that were deficient in hypoxanthine phosphoribosyl transferase (Hprt, E.C.2.4.2.8) activity at the frequency of approximately 6.2 x 10(-5). Approximately 10% of 6TGR cells showed plasticity in their mutant phenotypes and reverted to HAT-resistant (HATR), which is Hprt-proficient, wild type phenotype. Eventually we identified the plastic mutants in the un-irradiated wild type cell population as well and found that ionizing irradiation enhanced the frequency of the plastic mutation approximately 24 times. Treatment with 5-aza-cytidine did not affect the plasticity of mutant phenotypes identified in this study, suggesting that DNA methylation was not involved in the plastic changes of the mutant phenotypes. The plastic mutant phenotype identified in our study is a new type of genomic instability induced by ionizing irradiation, and it is likely to be involved in one of the primary changes that occur in the process of radiation carcinogenesis, and may explain one element of carcinogenesis, which is composed of multi-stages.

Identification of mouse mutant cells exhibiting plastic mutant phenotype II; ionizing radiation-induced mutant phenotype plasticity is not dependent on DNA methylation of the hypoxanthine phosphoribosyl transferase gene in mouse FM3A cells.

As we previously reported, we isolated and examined mouse mutant cells exhibiting phenotypic plasticity. Approximately 10% of 6-thioguanine resistant (6TG(R)) cells derived from the irradiated cell population exhibited phenotypic plasticity and reverted to wild type HAT resistance (HAT(R)). Similar mutant cells were also identified in an un-irradiated wild type cell population, but at a lower frequency. Ionizing irradiation enhanced the frequency of the plastic mutation approximately 24 times in our experiments. Treatment with 5-aza-cytidine did not affect phenotypic plasticity. In this study, we further performed detailed molecular analysis of the promoter region of the hypoxanthine phosphoribosyl transferase (Hprt) gene. The analysis revealed that most cytidine residues were not methylated, even in 6TG(R) mutant cells, in which Hprt activity must be down-regulated. These results suggested that DNA methylation was not involved in mutant phenotype plasticity, a new type of genomic instability induced by ionizing radiation. Plasticity in gene regulation may play an important role in radiation carcinogenesis, which is a multiple-stage process.

Loss-of-heterozygosity analysis of 6-thioguanine-resistant mutants induced by radon exposure in mouse FM3A cells.

Radon is an inert gas that can migrate from soils and rocks and accumulate in enclosed areas such as buildings and underground mines. The ubiquitous occurrence of radon in the environment is the primary cause of harmful radiation exposure to the public. To investigate the mutagenic effect of radon, mouse FM3A cells growing on soft agarose plates were exposed to alpha particles disintegrated from radon-222 and daughter elements. Mutation induction at the hypoxanthine phosphoribosyl transferase (Hprt) allele was examined at radon concentrations of 10, 230, 1,100, 6,500, 200,000, 1,000,000, and 10,000,000 Bq/m(3) for an exposure period of 1 week. A typical inverse dose-rate effect was observed in the frequencies of 6-thioguanine-resistant (6TG(R)) mutations, and lower mutation frequencies were exhibited at 230, 1,100, 6,500, and 200,000 Bq/m(3) than at 10, 1,000,000, and 10,000,000 Bq/m(3). Loss-of-heterozygosity (LOH) analysis at the Hprt locus revealed that deletion mutations were dominant at radon concentrations of 230, 1,100, 6,500, and 10,000,000 Bq/m(3), but not at 10, 200,000, and 1,000,000 Bq/m(3). These results suggested that alpha particles released from radon in the normal atmosphere did not exhibit the measured mutagenic effect in mouse FM3A cells, but that increased concentrations of radon led to a significant increase in the mutagenic effect of radon. At 6,500 Bq/m(3), radon exposure induced the least number of 6TG(R) mutants but all had LOH deletion mutations, which is the typically observed type of mutation in radiation carcinogenesis. Our results suggest that certain concentrations of environmental radon may have specific carcinogenic potential, and it should be avoided by proper ventilation wherever possible.

Air contamination analysis during emergency medical treatment.

After radiological emergencies, patients contaminated with radioactivity are taken to radiation emergency hospitals for treatment. Numerical simulations using the computer software 'Flow Designer((R))' were made in order to evaluate indoor air contamination caused by the breathing out of contaminated air. The National Institute of Radiological Sciences facility was used for the numerical evaluation. Results indicate that the dispersion of contaminated air depends on the characteristics of the contaminants, and that the dispersion range was limited and localised. Only medical staff standing in a special position near the patient was exposed to almost un-diluted contaminated air. Highly contaminated air was evacuated with a local exhaust pump system. Room air quality was monitored using a continuous air sampling system, but it was found that the sampling point was not representative for the purpose of radiation protection. From the air-flow analysis, some problems that affect radiological safety were revealed and valuable information and measures for preventing secondary contamination were determined.

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 an alpha spectrometer will give more useful information during the first response of an emergency.

Radon-thoron discriminative measurements in Gansu Province, China, and their implication for dose estimates.

Indoor radon measurements were carried out in cave dwellings of the Chinese loess plateau in Gansu province, where previously the Laboratory of Industrial Hygiene (LIH), China, and the U.S. National Cancer Institute (NCI) had conducted an international collaborative epidemiological study. The LIH-NCI study showed an increased lung cancer risk due to high residential radon levels, and estimated the excess odds ratio at 100 Bq/m3 to be 0.19 (Wang et al., 2002). The present study used two types of newly developed passive monitors: One is a discriminative monitor for radon and thoron; the other is a selective monitor for thoron decay products. The arithmetic mean concentrations of indoor radon and thoron were 91 and 351 Bq/m3, respectively. As reported by our previous study in Shanxi and Shaanxi provinces (Tokonami et al., 2004), the presence of high thoron concentration was confirmed and thoron was predominant over radon in the cave dwellings. However, the mean equilibrium equivalent thoron concentration (EETC) was found to be much lower than expected when assuming the equilibrium factor of 0.1 provided by the UNSCEAR (2000) report. The effective dose by radon and thoron decay products was estimated to be 3.08 mSv/yr. It was significantly lower than the dose of 8.22 mSv/yr estimated from the measurements that did not take into consideration any discrimination between radon and thoron. Excess relative risk of lung cancer per sievert may be much higher than the risk estimated from the LIH-NCI study, considering that discriminative measurements were not used in their study.