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Journal Articles

Estimation of $$^{222}$$Rn flux and its effect on the atmospheric $$^{222}$$Rn concentration at Hachijo-jima island, Japan

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Iida, Takao*

Hoken Butsuri, 45(3), p.270 - 277, 2010/09

Measurements of $$^{222}$$Rn flux from the ground and $$^{226}$$Ra content in soil were made on Hachijo-jima, which is a solitary island in the Pacific about 200 km to the south of the main island of Japan, to evaluate effect of locally exhaled $$^{222}$$Rn to the surface air concentration of $$^{222}$$Rn measured on this island. Averages of $$^{222}$$Rn flux and $$^{226}$$Ra content in dry soil were 0.88 mBq m$$^{-2}$$ s$$^{-1}$$ and 6.8 Bq kg$$^{-1}$$ at Hachijo-jima and 9.7 mBq m$$^{-2}$$ s$$^{-1}$$ and 23.2 Bq kg$$^{-1}$$ at Nagoya, respectively. The low level $$^{226}$$Ra content in soil is one of main causes for the small $$^{222}$$Rn flux at the island. With this $$^{222}$$Rn flux, the contribution of locally exhaled $$^{222}$$Rn from the island was estimated by a simple model to occur at concentration of 0.035 to 0.072 Bq m$$^{-3}$$ (relative contribution is 4 to 12%) under typical nocturnal condition. Under diurnal condition effect is lower than that of nocturnal condition. This local $$^{222}$$Rn component is negligible as compared with concentration of long-range transported $$^{222}$$Rn of 0.5 to 3 Bq m$$^{-3}$$.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Taiki Kankyo Gakkai-Shi, 44(1), p.42 - 51, 2009/01

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Journal Articles

Simulation of the atmospheric dispersion of $$^{85}$$Kr from a reprocessing plant over a coastal area; Performance examination of an emergency environmental radiation dose evaluation code system "SIERRA-II"

Takeyasu, Masanori; Iida, Takao*; Watanabe, Hitoshi; Takeishi, Minoru; Yamamoto, Asao*

Journal of Radioanalytical and Nuclear Chemistry, 275(1), p.43 - 54, 2008/01

 Times Cited Count:1 Percentile:88.77(Chemistry, Analytical)

The performance of the computer code system "SIERRA-II" for calculating the environmental radiation dose due to an accident was assessed using the environmental monitoring data around the coastally located Tokai Reprocessing Plant (TRP) when $$^{85}$$Kr was discharged during its operation. The agreement within a factor of 5 between the calculated and observed air concentrations of $$^{85}$$Kr in areas of a few km from the TRP was achieved in 57% of the comparison data, and the agreement within a factor of 2 was obtained in 29%, disregarding the internal boundary layer. According to the vertical profile of atmospheric temperatures, the internal boundary layer was modeled in the SIERRA-II and the agreement became better than when the internal boundary layer was not considered.

Journal Articles

Development of three-dimensional numerical model for $$^{222}$$Rn and its decay products coupled with a mesoscale meteorological model, 1; Model description and validation

Nishizawa, Masato; Nagai, Haruyasu; Chino, Masamichi; Moriizumi, Jun*; Yoshioka, Katsuhiro*; Okura, Takehisa; Yamazawa, Hiromi*; Iida, Takao*; Mukai, Hitoshi*; Tojima, Yasunori*; et al.

Journal of Nuclear Science and Technology, 44(11), p.1458 - 1466, 2007/11

 Times Cited Count:4 Percentile:66.18(Nuclear Science & Technology)

A three-dimensional Eulerian numerical model for $$^{222}$$Rn and its decay products coupled with a mesoscale meteorological model has been developed and applied to the reproduction of the daily and monthly variations of $$^{222}$$Rn concentration, the monthly variation of $$^{210}$$Pb deposition in Japan and the temporal variation of $$gamma$$ dose rate after the cold front passage in the coastal area of the Japan Sea for the verification of model capability. The results are as follows: (1) The model reproduced the monthly variation of surface $$^{222}$$Rn concentration in remote islands, but underestimated inland concentration due to coarse vertical resolution near the surface of the model. (2) The model reproduced the seasonal variation of the observed and the long-term yearly averaged $$^{210}$$Pb depositions as long as precipitations are predicted precisely. (3) The model reproduced the rise of $$gamma$$ dose rate in precipitation accompanied with the cold front passage. In particular, $$^{222}$$Rn decay products in melted snow and graupel contributed the rise of $$gamma$$ dose rate.

Journal Articles

Ratio of aerosol and gases of radioactive chlorine and particle size distribution of aerosol formed by high-energy proton irradiation

Yokoyama, Sumi; Sato, Kaoru; Manabe, Kentaro; Noguchi, Hiroshi; Kaneko, Hirohisa; Oki, Yuichi*; Iida, Takao*; Tanaka, Susumu*

Radiation Protection Dosimetry, 127(1-4), p.392 - 397, 2007/11

 Times Cited Count:0 Percentile:100(Environmental Sciences)

To estimate internal doses due to the inhalation of radionuclides produced by the nuclear spallation of the air nuclei in high-energy proton accelerator facilities, the physicochemical properties of radionuclides are very important. However, there is not enough information of the properties for airborne radioactive chlorine formed from argon gas in the air of a high-energy proton irradiation field. Thus we have measured the ratio of aerosol and gases of radioactive chlorine which are formed by irradiating argon gas-added air with a 48 MeV proton beam. In addition, the particle size distribution and chemical form of non-radioactive aerosol were examined. It was found that Cl-38 and Cl-39 exist as aerosol, acidic and non-acidic gases. The percentages of Cl-38 and Cl-39 aerosols are more than 70%. In total radioactive chlorine gas, about 30% and 70% are acidic and non-acidic gases, respectively. The concentration of non-radioactive aerosol had a peak at an aerodynamic diameter of 20-30 nm in the early irradiation period. The particle size of non-radioactive aerosol shifted to larger with time. After 10 min, the aerosols grew very slowly and many of the non-radioactive aerosols were distributed widely under 200 nm. This suggests that the diameter of the radioactive chlorine aerosol formed by the attachment of the radioactive chlorine to the non-radioactive aerosol around a beam line of the accelerator is much smaller than the default value adopted in ICRP Publication 66.

Journal Articles

Epidemiological studies on indoor radon risk; A Review and current issues

Yonehara, Hidenori*; Ishimori, Yuu; Akiba, Suminori*; Iida, Takao*; Iimoto, Takeshi*; Kai, Michiaki*; Shimo, Michikuni*; Tokonami, Shinji*; Yamada, Yuji*; Yoshinaga, Shinji*; et al.

Hoken Butsuri, 42(3), p.201 - 213, 2007/09

The pooled analysis recently carried out in European countries and North American countries showed the excess relative risk of lung cancer increased by 10-20% per 100 Bqm$$^{-3}$$ increase in indoor radon concentration. The Scientific Committee on Indoor Radon Risk and Response to the Issue established by the Japan Health Physic Society reviewed the scientific evidence on the indoor radon risk obtained so far and evaluated the pooled analysis results from the viewpoint of estimating the risk coefficient in Japan. The committee concludes that the risk shown by the pooled analysis results has the consistency from miners risk analysis, and that it is probably not low in the reliability and validity, although the value may include the uncertainties caused from the correction of radon concentration measured, from the effect of thoron on measurement results, from the differences of environmental parameters in exposure, and so on.

Journal Articles

Suppression of radon exhalation from soil by covering with clay-mixed soil

Ota, Masakazu*; Iida, Takao*; Yamazawa, Hiromi*; Nagara, Shuichi; Ishimori, Yuu; Sato, Kazuhiko; Tokizawa, Takayuki

Journal of Nuclear Science and Technology, 44(5), p.791 - 800, 2007/05

 Times Cited Count:12 Percentile:32.79(Nuclear Science & Technology)

A study on the effectiveness of clay-mixed soil as a barrier against radon exhalation from soil surface was carried out at a closed uranium mine in Japan. Continuous observations of radon flux at a clay-covered soil surface and a bare soil surface, radon concentration in soil air and soil moisture content were carried out for 80 days. The mean of radon flux of the clay-covered plot was one fifth of that of the bare plot. This result indicates that clay-mixed soil worked effectively for reduction of radon exhalation from the soil surface. A numerical analysis with a one-dimensional radon transport model for unsaturated soil was carried out to evaluate the effectiveness of the barrier under dry weather conditions. Calculation results suggested that the barrier works effectively even under the dry condition.

Journal Articles

A New digital autoradiographical method for identification of Pu particles using an imaging plate

Koarashi, Jun; Saito, Fumihiro; Akiyama, Kiyomitsu; Rahman, N. M.*; Iida, Takao*

Applied Radiation and Isotopes, 65(4), p.413 - 418, 2007/04

 Times Cited Count:23 Percentile:15.49(Chemistry, Inorganic & Nuclear)

no abstracts in English

Journal Articles

Diurnal and seasonal variations in $$^{222}$$Rn concentration profile in soil

Iskandar, D.*; Yamazawa, Hiromi*; Yamasoto, Kotaro; Ota, Masakazu*; Koarashi, Jun; Moriizumi, Jun*; Bunawas*; Iida, Takao*

Hoken Butsuri, 42(1), p.98 - 104, 2007/03

The $$^{222}$$Rn concentrations in soil and $$^{222}$$Rn flux were measured at 6 depths in soil to analyze the seasonal- day-to-day and diurnal variations. The variations of $$^{222}$$Rn concentrations in soil were larger in shallow depths. It seems that the $$^{222}$$Rn concentration in soil during night-time was slightly lower than day-time especially at depth of 15 cm. The precipitation may have affected the concentration insoil differently depending on its amounts. The large decrease in air pressure during one day increased the concentration in soil at shallow soil layers. The effect of soil water content on $$^{222}$$Rn concentration in soil was also observed.

Journal Articles

Evaluation of aerosol sizing characteristic of an impactor using imaging plate technique

Rahman, N. M.*; Iida, Takao*; Saito, Fumihiro; Koarashi, Jun; Yamasaki, Keizo*; Yamazawa, Hiromi*; Moriizumi, Jun*

Radiation Protection Dosimetry, 123(2), p.171 - 181, 2007/02

 Times Cited Count:11 Percentile:35.52(Environmental Sciences)

no abstracts in English

Journal Articles

Analysis of Rn-222 concentration in the upper atmosphere during rainfall using the wet scavenging model for its decay products

Takeyasu, Masanori; Iida, Takao*; Takeishi, Minoru

Proceedings of 2nd Asian and Oceanic Congress Radiological Protection (AOCRP-2) (CD-ROM), p.754 - 757, 2006/10

The atmospheric Rn-222 concentration in rain clouds was estimated using the wet scavenging model of Rn-222 decay products with the observed data of the environmental $$gamma$$ ray dose rate. In this method, the pattern of the increase of the dose rate calculated by the model was adjusted to the observed one, in order to estimate the atmospheric Rn-222 concentration which was one of parameter of the model. The Rn-222 concentration was estimated for the rainfall event on Dec. 27, 2003, when a large increase of the dose rate was observed in Tokai-mura. The concentration was estimated to be 24 Bq m$$^{-3}$$, which was higher than the measured one at a height of a few kilometers around central Japan by aircraft. From a back trajectory analysis, the origin of Rn-222 atoms for the events on Dec. 27 was back-tracked to the northeastern part of China, and it was guessed that the large amount of Rn-222 was transported by the Eurasian continental air mass.

Journal Articles

Concentrations and their ratios od $$^{222}$$Rn decay products in rainwater measured by $$gamma$$-ray spectrometry using a low-background Ge detector

Takeyasu, Masanori; Iida, Takao*; Tsujimoto, Tadashi*; Yamasaki, Keizo*; Ogawa, Yoshihiro*

Journal of Environmental Radioactivity, 88(1), p.74 - 89, 2006/00

 Times Cited Count:21 Percentile:52.02(Environmental Sciences)

The concentrations of $$^{214}$$Pb and $$^{214}$$Bi in rainwater was measured by a low background Ge detector. The concentrations of $$^{214}$$Pb and $$^{214}$$Bi were inverse relations with rainfall rate in some rainfall events, and the concentration ratio of $$^{214}$$Bi to $$^{214}$$Pb would be a weak inverse relation with rainfall rate. The model was considered about the scavenging effects of rainfall to Radon decay products, and those results were discussed with the model.

Journal Articles

Measurement of radiolytic yield of nitric acid in air

Kanda, Yukio*; Oki, Yuichi*; Yokoyama, Sumi; Sato, Kaoru; Noguchi, Hiroshi; Tanaka, Susumu*; Iida, Takao*

Radiation Physics and Chemistry, 74(5), p.338 - 340, 2005/12

 Times Cited Count:5 Percentile:62.18(Chemistry, Physical)

The operation of high-energy accelerators leads to the production of radiolytic noxious gases, such as ozone and nitrogen compounds in the air of the beam-line tunnels. Among nitrogen compounds, nitric acid is a principal radiolytic compound produced in large quantities. In the high-intensity proton accelerator, such as J-PARC, a very strong radiation environment leads to an abundant production of nitric acid. A quantitative assessment of the damage due to corrosion with nitric acid is essential for machine maintenance and information concerning the formation of nitric acid is a requisite for that. In this work, the G-value for nitric acid production was measured by irradiating atmospheric air with 48MeV-protons. The G-value was obtained to be 1.46$$pm$$0.12. The G-value for nitric acid production obtained in this experiment was larger than the estimated value, but very close to the value of 1.5 given by irradiating the air with Co-60-$$gamma$$rays.

Journal Articles

Characterization of radionuclides formed by high-energy neutron irradiation

Yokoyama, Sumi; Sato, Kaoru; Noguchi, Hiroshi; Tanaka, Susumu; Iida, Takao*; Furuichi, Shinya*; Kanda, Yukio*; Oki, Yuichi*; Kaneto, Taihei*

Radiation Protection Dosimetry, 116(1-4), p.401 - 405, 2005/12

 Times Cited Count:1 Percentile:88.68(Environmental Sciences)

The physicochemical property of radionuclides suspended in the air is an important parameter to evaluate internal doses due to the inhalation of the airborne radionuclides and to develop the air monitoring system in high-energy proton accelerator facilities. This study focuses on the property of radioactive airborne chlorine ($$^{38}$$Cl and $$^{39}$$Cl) and sulfur ($$^{38}$$S) formed from Ar gas by irradiation with high-energy neutrons. As a result of the irradiation to a mixture of Ar gas and dry air, $$^{38}$$Cl and $$^{39}$$Cl existed as non-acidic gas and $$^{38}$$S was present as acidic gas. Further, it was found that in the high-energy neutron irradiation to aerosol containing-Ar gas, the higher the amount of radioactive aerosols becomes, the lower that of radioactive acidic gas becomes.

JAEA Reports

Study on the measurement method of diffusion coefficient for radon in the soil (VII)

Iida, Takao*

JNC-TJ6400 2004-002, 49 Pages, 2005/01

JNC-TJ6400-2004-002.pdf:1.78MB

To evaluate radon exhalation from the ground surface of a soil-covered landfill for waste rock from a uranium mine, the followings were carried out: (1) continuous measurement of radon concentration in soil air, radon exhalation from ground surface and soil moisture content, (2) experimental evaluation of the effect of bentonite-mixed cover soil to radon exhalation, and (3) numerical simulations on these items. According to the measurement results, the radon exhalation rate varied in the rage from 0.004 to 0.351 Bq m-2s-1 with an average value of 0.010 m-2s-1. These values are considerably smaller than those obtained in the measurements in previous years. This can be attributed to wetting of the ground surface due to precipitation much greater than that in the previous years. The radon exhalation from the cover soil surface, on the other hand, was measured to be as small as 0.0015 to 0.0030 Bq m-2s-1 for the variation range and 0.0020 Bq m-2s-1for the average. The radon concentration in soil air was 200 to 400 kBq m-3 and varied in accordance with the exhalation. Therefore, it can be concluded that the soil cover effectively and sufficiently reduce the radon exhalation. The numerical simulations showed results pertinent to the observational results except for some short-term variations. By summarizing the results obtained in the series of studies (I to VII), it was concluded that main parts of radon transfer in the surface soil were understood and the reduction of radon exhalation by cover soil was effective. The remaining issues are development of soil radon monitor which is applicable to nearly saturated soils, measurement of physical properties of cover soils, and study on maintenance of soil cover soundness.

Journal Articles

Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest

Koarashi, Jun; Iida, Takao*; Asano, Tomohiro

Journal of Environmental Radioactivity, 79(2), p.137 - 156, 2005/00

 Times Cited Count:15 Percentile:63.57(Environmental Sciences)

To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions were measured for bulk, acid-insoluble and base-insoluble organic matter fractions separated by a chemical fractionation method. The measurements also made it possible to estimate indirectly radiocarbon (14C) abundances of chemically soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of 14C abundances showed that bomb-derived 14C has been penetrated into the first 16 cm mineral soil at least, whereas a significant amount of it has been still preserved as the acid-soluble organic matter around litter-mineral soil boundary. In contrast, no or little bomb-derived 14C was observed for the base-insoluble fraction in all sampling depths, indicating that this recalcitrant fraction, accounting for approximately 15 % of total carbon in this temperate-zone forest soil, plays a role as a long-term sink in the carbon cycle. These results suggest that bulk soil organic matter can not provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.

JAEA Reports

Study on the measurement method of diffusion coefficient for radon in the soil (IV)

Iida, Takao*

JNC-TJ6400 2004-001, 66 Pages, 2004/03

JNC-TJ6400-2004-001.pdf:3.16MB

The aim of this study is to clarify the radon behavior in the soil at the waste rock yards of uranium mine. We have developed an apparatus for measuring radon diffusion coefficient in soil under the control of soil temparature. The radon diffusion coefficients changed suddenly around the soil temperature of 0 degrees centigrade. The radon diffusion coefficients in dry soil have little temparature dependency, and were comparable coefficients obtained by empirical formula of Rogers & Nielson. To study the restraint effect of radon exhalation by covering with bentonite on soil, we carried out the measurements and the calculations by using one-dimensional transport model of atmosphere and soil. The decrease of radon exhalation rate was 2.9 Bq m-2 s-1 when soil covered with the bentonite of 5 cm thick. The radon consentrations in snow cover and the radon flux from the snow surface were measured at the waste rock yard in Ningyo-toge Environmental Engineering Center. The simulation of the radon transport in snow also carried out using measured snow parameters. The radon concentrations in snow cover ranged from 500 to 3,000 Bq m-3, and the radon flux from the snow surface was about 9 mBq m-2 s-1. The small radon flux results mainly from the wet condition of soil surface caused by melting of the snow.

Journal Articles

Development of a Real-Time Environmental Radiation Dose Evaluation System for the Vicinity of a Nuclear Facility; A Study of a Real-Time Environmental Radiation Dose Evaluation System

Takeyasu, Masanori; Takeishi, Minoru; Shimizu, Takehiko; Iida, Takao*

Hoken Butsuri, 39(4), p.382 - 390, 2004/00

A computer code system was developed to evaluate a real-time environmental radiation dose when radioactive substances were accidentally released from a nuclear facility. The examination of the system was performed by using the data of air absorbed dose rate observed at monitoring stations and monitoring posts around the Tokai Reprocessing Plant when $$^{85}$$Kr was discharged during its normal operation.

Journal Articles

Measurements of concentrations and its ratio of radon decay products in rainwater by gamma-ray spectrometry with a low background germanium detector

Takeyasu, Masanori; Iida, Takao*; Tsujimoto, Tadashi*; Yamasaki, Keizo*

International Congress Series, 1276, p.289 - 290, 2004/00

The each concentration of $$^{214}$$Pb and $$^{214}$$Bi in rainwater was measured by a low background Ge detector. The concentration of$$^{214}$$Pb was a inverse relation with rainfall rate in some rainfall events, and the concentration ratio of$$^{214}$$Bi to$$^{214}$$Pb was a weak inverse relation with rainfall rate in all rainfall events. These relations were the same as these obtained by the removal model of radon decay products from stratiform cloud.

49 (Records 1-20 displayed on this page)