About two hundred KURAMA-IIs now serve continuous monitoring in residential areas with local buses as well as periodic monitoring in East Japan by the Japanese government. Based on the success of KURAMA, KURAMA-II was developed to perform continuous monitoring in residential areas. The KURAMA-II rests on the architecture of the KURAMA, but the interior of the vehicle is completely redesigned.
We then conducted a field test of continuous monitoring by KURAMA-II on a local bus in Fukushima City in cooperation with Fukushima Kotsu Co. in December 2011. MEXT started a car survey project in March 2012, in which 100 units of KURAMA-II were loaned to municipalities in eastern Japan [7]. The development of KURAMA-II is supported by the "Japan recovery grant program" of National Instruments, Japan.
The field tests of KURAMA-II on local buses are supported by Fukushima Kotsu Co.
Koyama and the staff members of the KURAMA operations team of the Fukushima Prefectural Government for their continued support of KURAMA's field testing in Fukushima. Maeno of the Graduate School of Science, Kyoto University; and the staff members of the KURAMA field test team from RRI, Kyoto University for their contributions to the Fukushima test operation. Takahashi and the staff of Matsushimaya Inn, Fukushima, for their heart-warming hospitality during the activities in Fukushima, regardless of their dire circumstances due to the earthquake and subsequent nuclear accident.
Open Access This chapter is distributed under the terms of the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
In Situ Environmental Radioactivity
Measurement in High–Dose Rate Areas Using a CdZnTe Semiconductor Detector
- Introduction
- Materials and Methods
- Results and Discussion
- Summary
A CZT detector with a small detector element is also less sensitive to gamma rays from radiocesium. This paper describes research on the adaptability of the CZT detector to in situ environmental radioactivity measurement. Before the measurements, we evaluated the energy dependence of the peak efficiency and the angular dependence of the peak efficiency for the CZT detector.
Figure 11.1 shows the appearance and cross-sectional drawing for the CZT detector assembly (Kromek GR1TM) used in this study. To acquire the pulse height spectra from the CZT detector and to provide power, a laptop computer was connected to the detector with a USB cable. The ambient dose equivalent rates at the measurement points were Table 11.1 Comparison of the characteristics of a conventional Ge semiconductor detector and a CZT detector.
The air kerma velocities at measuring points were estimated from the measured surface contaminant densities on the bottom by the CZT detector. The G(E) function for the CZT detector was derived from the calculated response matrix of the CZT detector to monoenergetic gamma rays ranging from 50 keV to 3 MeV. As basic characteristics of the detectors for in situ measurement of environmental radioactivity, the energy and angle dependence of the peak efficiency of the full energy absorption of the CZT detector were evaluated.
On the other hand, rather low values with energies above about 1500 keV show that the CZT detector has a lower sensitivity to energetic gamma rays from. This indicates that the CZT detector has a smaller angular dependence on gamma rays with energies between 662 and 1333 keV. The results shown in Figures 11.1 and 11.2 suggest that the CZT detector can allow us to correctly measure pulse height spectra in heavily polluted areas.
As shown in Figure 11.1, the CZT detector is less sensitive to energetic gamma rays than about 1500 keV. The CZT detector was unable to detect events enough to form the peak due to gamma radiation with an energy of 1460 keV from 40K. It would be a crucial disadvantage that the CZT detector would not be able to clearly identify peaks due to 40K gamma rays in the case of general measurements of radioactivity in the environment.
From this point of view, the CZT detector enables easy confirmation of the effect of the decontamination work with certain accuracy.
Safety Evaluation of Radiation Dose Rates in Fukushima Nakadori District
- Introduction
- Radiation Level of Fukushima Nakadori District
- International Support Activities
- IAEA’s International Expert Mission Team for Fukushima Remediation Issues [5]
- Community Dialog Forum for Residents of Fukushima Prefecture at Fukushima-shi [6]
- Risk Evaluation of 1 mSv/y for Public Radiation Exposure Limits
- Country-Averaged Annual Exposure Doses of Natural Radiation in the World
- Discussion
- Conclusion
The accident caused serious contamination by radioactive cesium isotopes in very large areas of Fukushima Prefecture and adjacent prefectures in the Tohoku and North Kanto regions. Remediation works are being carried out to reduce the ambient radiation level in the living areas of the areas where the additional annual radiation exposure doses for individuals exceed 1 mSv per year (i.e. 1 mSv/y). In the area where the work has been assigned to Fukushima Prefecture, approximately 70% of the remediation work plan up to FY 2014 (i.e., up to March 2015) has been completed for the residential sites [1].
12 Safety Assessment of Radiation Dose Levels in Nakadori District of Fukushima 135 received psychological support through the dialogue meeting with the residents of Fukushima Prefecture, mainly to discuss radiation issues regarding its impact on health and radiation protection in their daily lives. This data should be very helpful for residents to recognize that the current status of Fukushima Prefecture is safe and to assess how they will live there. It plays an important role in the government and economy, including industrial activities and agriculture of Fukushima Prefecture.
From the figure and table it can be said that radiation levels in the living space of the Nakadori district are generally below 0.23Sv/h so that the additional annual dose is expected to be below 1 mSv/y. The authors think that the non-objective explanation without comprehensible data that clearly shows a safety of the dose "1 mSv/y" is not effective in this case. It seemed that the higher values were not convincing because the Japanese did not know such local high radiation areas in India and China, nor the natural radiation levels in the European countries of the ICRP members.
On this basis, a risk in the order of 106 to 105 per year would probably be acceptable to any individual member of the public. The ICRP members repeatedly said during the dialogue meetings with the residents of Fukushima Prefecture that the annual exposure doses in Fukushima were as low as that of natural radiation in their countries in Europe. Accordingly, the authors evaluated the country average annual exposure doses to the world's natural radiation, based on the basic data on indoor radon concentration, external exposure both outdoors and indoors, cosmic radiation and the intake of food ingested. from reference [14].
The resulting additional annual dose is expected to be below 1 mSv/year in most parts of Nakadori District and an average of 2 mSv/year even in the three municipalities. A difficult problem is how to deal with the impact of the total dose of low radiation exposure that accumulates over a person's lifetime. Decontamination work is being carried out throughout the living space of Fukushima Prefecture, with a target in the 2018 fiscal year.
Recent measurements of the environmental radiation dose rates showed that the additional annual exposure dose was generally below 1 mSv/year in the majority of the Nakadori district and about 2.0 mSv/year in the special decontamination area of Tamura-shi, Naraka-machi, and Kawauchi - walls.
Indoor Deposition of Radiocaesium
- Introduction
- Methods
- Locations of Houses Investigated
- Measurement of Surface Contamination
- Results and Discussion
- Indoor Surface Contamination for Odaka Houses
- Effect of Surface Contamination on the Indoor Ambient Dose Equivalent
- Conclusion
To estimate surface contamination, a dry swab test was performed on the surface of materials in the rooms and in the roof space. The number of houses and samples collected for surfaces of wood, metal, glass and plastic materials in the rooms, of wooden structures in the roof space and of wooden columns in the rooms for each area are summarized in Table 13.1. The number of swab samples collected from surfaces of wood, metal, glass and plastic materials in the rooms, from wooden structures in the roof space and from wooden columns in the rooms for each room, which were above the detection limit and below the detection limit in each area summarized in Table 13.1.
Eighty-nine percent (729/815) of the swabs obtained in the rooms exceeded the detection limit, and a maximum value was estimated to be 1.54 Bq/cm2. Seventy-seven percent (95/124) of the smear samples taken from wooden structures in the roof space exceeded the detection limit, and a maximum value was estimated to be 1.14 Bq/cm2. This result indicates that the pollution is not only deposited in the interior of the house, but also in the structure of the roof space.
However, only some of the smear samples exceeded the detection limit for wood column in the rooms with a maximum value of 0.07 Bq/cm2. The median surface contamination with an interquartile range evaluated from surfaces of wood, metal, glass and plastic materials in the rooms for 27 houses in each area is shown in Fig.13.2a. In the same way, the median surface contamination with an interquartile range is evaluated from surfaces of wooden structure in the roof space for houses in each area shown in Fig.13.2b.
The order of indoor surface pollution was the same between in the rooms and in the roof space except a value for the house in Yoshina, as shown in Fig.13.2a,b. The houses of Kanaya and Mimigai show a difference in the median surface contamination with an interquartile range in Fig.13.2a, bare comparison. The value of median surface contamination with an interquartile range for each house in two areas is displayed in the left group and the right group, respectively.
13.2 (a) Median surface contamination with an interquartile range assessed from surfaces of wood, metal, glass and plastic materials in the rooms of 27 houses in each area. A large discrepancy in the values of surface pollution for each observed house, seen in fig. 13.3, is not seen in fig. 13.4.
![Fig. 10.8 A result of the continuous monitoring by KURAMA-II on local buses conducted by the Fukushima prefectural government [1]](https://thumb-ap.123doks.com/thumbv2/1libvncom/10208296.0/9.659.81.580.94.465/result-continuous-monitoring-kurama-conducted-fukushima-prefectural-government.webp)
![Fig. 10.9 Map of air dose rates on roads measured by KURAMA-II in the periodical survey conducted by NRA between August and October 2012 [9]](https://thumb-ap.123doks.com/thumbv2/1libvncom/10208296.0/10.659.84.578.88.797/rates-measured-kurama-periodical-survey-conducted-august-october.webp)
