Soil Sample Results for Plutonium 238, 239+240 and 241 within the 80 km Radius from Fukushima Dai-ichi NPP. ( September 2013 )
- This data was created based on soil deposition densities of plutonium 238, plutonium 239+240, and plutonium 241 as measured in "Establishment of A Comprehension Approach of Long Term Effects by Radioactive Substances Due to Fukushima Daiichi Nuclear Power Plant Accident" lead by the Secretariat of the Nuclear Regulation Authority.
- In order to elaborate the soil concentration map, soil sampling points were selected around the prior sampling points of the first, second and third soil surveys where plutonium 238 and 239+240 were detected (100 locations).
- The soil sampling was conducted from September 10 to September 12, 2013.
- The soil sample was taken using a metal cylindrical sampler of a diameter of 5 cm and a height of 5 cm by hammering the shaft of lid of the sampler. Sampling was conducted at two approximated points to each prior sampling point of the first , second and third soil surveys where plutonium 238 and 239+240 were detected and where was bare soil without grasses and stones. The soil sample was put in the 500 mL container, mixed well with a Teflon rod, and then the container was sealed as analysis sample for plutonium 238, plutonium 239+240, and plutonium 241.
- Of the above soil samples, regarding plutonium 238 and 239+240, radiochemical analysis was conducted for 100 g of each of the collected soil samples, using a silicon semiconductor detector after separating the plutonium. The measurement was carried out for nearly 20 hours. The detection limit was set at about 0.6 Bq/m2.
- Of the above soil samples, regarding plutonium 241, radiochemical analysis was conducted for 100 g of each of the collected soil samples. After separating the plutonium, a liquid scintillation counter was used to measure beta-ray for plutonium 241. The measurement was carried out for nearly 500 minutes. The detection limit was set at around 30 Bq/m2 for plutonium 241.
- Regarding plutonium 238 and plutonium 241, unlike the third survey, analysis of this survey was conducted without considering half-life (plutonium 238: 87.7 years, plutonium 241: 14.36 years) adjustment as of June 14, 2013 that is the base date of the soil concentration map project. Instead, radioactivity concentration of plutonium 241 was adjusted as of the sampling date. Regarding plutonium 239 and plutonium 240, the analysis was conducted for the total of these two nuclide without considering half-life adjustment because their half-lives (plutonium 239: 2.411×104 years, plutonium 240: 6564 years) were extremely long and also the regular analysis method for alpha-ray emitting nuclides cannot distinguish the amounts of plutonium 239 and 240 that have almost the same alpha-ray energies.
- The analysis results were written to two significant figures. In the case when the count value was equal to or below three times the counting error, "ND" (Not detected) was stated with the detection limit.
Soil Sample Results for Plutonium 238, 239+240 and 241 within the 80 km Radius from Fukushima Dai-ichi NPP. ( September 2012 )
- This data was created based on soil deposition densities of plutonium 238 and plutonium 239+240 as measured in "Establishment of A Comprehension Approach of Long Term Effects by Radioactive Substances Due to Fukushima Daiichi Nuclear Power Plant Accident" lead by the Ministry of Education, Culture, Sports, Science and Technology in Japan.
- In order to elaborate the soil concentration map, soil sampling points were selected around the prior sampling points of the first and second soil surveys where plutonium 238 and 239+240 were detected (97 locations).
- The soil sampling was conducted from September 19 to September 21 and from September 25 to September 28, 2012.
- The approximately 200 g soil sample was taken using a cylindrical sampler of a diameter of 5 cm and a height of 5 cm at each sampling point selected around the prior sampling points of the first and second soil survey where plutonium 238 and 239+240 were detected. After mixing each sample well, approximately 100 g was used for analyzing plutonium 238 and 239+240, and then another 100 g was used for analyzing plutonium 241.
- In order to lower the detection limit, the weight of soil sample for analysis was doubled (approximately 100 g) from approximately 50 g of the second soil survey.
- Of the above soil samples, regarding plutonium 238 and 239+240, radiochemical analysis was conducted for 100 g of each of the collected soil samples, using a silicon semiconductor detector after separating the plutonium. The measurement was carried out for 80,000 seconds (nearly 22 hours). The detection limit was set at about 0.6 Bq/m2.
- Of the above soil samples, regarding plutonium 241, radiochemical analysis was conducted for 100 g of each of the collected soil samples. After separating the plutonium, a liquid scintillation counter was used to measure beta-ray for plutonium 241. The measurement was carried out for nearly 500 minutes. The detection limit was set at around 30 Bq/m2 for plutonium 241.
- Regarding plutonium 238 and plutonium 241, similar to the second survey, the results of this survey were adjusted in consideration of the half-life period (plutonium 238: 87.7 years, plutonium 241: 14.36 years) as of June 14, 2011 - the base date for the first survey's soil concentration map for plutonium. Regarding plutonium 239 and plutonium 240, the analysis was conducted for the total of these two nuclide without considering half-life adjustement because their half-lives (plutonium 239: 2.411×104 years, plutonium 240: 6564 years) were extremely long and also the regular analysis method for alpha-ray emitting nuclides cannot distinguish the amounts of plutonium 239 and 240 that have almost the same alpha-ray energies.
- The analysis results were written to two significant figures. In the case when the count value was equal to or below three times the counting error, "ND" (Not detected) was stated with the detection limit.
Soil Sample Results for Plutonium 241 in Eastern Japan ( From March 2012 to May 2012 )
- This data was created based on results of soil deposition densities of plutonium 241 measured in "The Second Survey on the Distribution Condition of Radioactive Substances by MEXT due to the Accident at TEPCO’s Fukushima Dai-ichi NPP".
- Regarding plutonium 241, we have analyzed plutonium 241 mainly by reusing the following samples (total 62 samples) where plutonium 238 and 239+240 had been detected in the first soil survey (collection date: first period:June 6 to June 14, second period:June 27 to July 8).
- (1) Samples that had been analyzed for plutonium 238 and 239+240, where plutonium 238 and 239+240 were detected in the first soil survey (54 samples).
- (2) Samples that had been analyzed for plutonium 238 and 239+240 for soil samples that had been newly analyzed for plutonium 238 and 239+240 in this survey and collected from the areas within 80-100 km from the Fukushima Dai-ichi NPS (8 samples).
- Of the above soil samples, regarding plutonium 241, through re-using the sample (electrodeposited plate) that was used to measure the alpha-rays for plutonium 238 and 239+240, and after chemically separating it, a liquid scintillation counter was used to measure the beta-rays for plutonium 241. The measurement was carried out for nearly 500 minutes. The detection limit was set at around 50 Bq/m2 for plutonium 241. (Note that in this survey, the detection limit may become higher due to the fact that samples used to measure alpha-rays for plutonium 238 and 239+240 were reused for analyzing plutonium 241.)
- Deposition density, error and detection limit at time of measurement.
- "ND" in the column "Deposition density", "-" in the column "Error", and detection limit value as reference in the column "detection limit": The peak of relevant nuclide was not clearly detected or calculated deposition was equal to or below 0.0.
- Reference value in the column "Deposition density" smaller than the detection limit in the column "detection limit": The peak of the relevant nuclide was detected even though the calculated deposition was below detection limit.
Soil Sample Results for Plutonium 238 and 239+240 in Eastern Japan ( From January 2012 to March 2012 )
- This data was created based on results of soil deposition densities of plutonium 238 and plutonium 239+240 measured in "the Second Survey on the Distribution Condition of Radioactive Substances by MEXT due to the Accident at TEPCO’s Fukushima Dai-ichi NPP".
- Regarding plutonium 238 and plutonium 239+240, of the soil samples collected in the first soil survey (collection date: first period:June 6 to June 14, second period:June 27 to July 8), the following soil samples where nuclide analysis was not conducted were analyzed:
- (1) Soil samples that were collected from areas within 80-100 km from the Fukushima Dai-ich NPS (8 samples).
- (2) Soil samples that were collected from grids adjoining the grid where plutonium 238 and 239+240 that were thought to have originated from the accident at Fukushima Dai-ichi NPS accident were detected in the first soil survey (54 samples).
- Of the above soil samples, regarding plutonium 238 and 239+240, radiochemical analysis was conducted for 50 g of each of the collected soil samples, using silicon semiconductor detectors to measure alpha-rays. The measurement was carried out for nearly 20 hours. The detection limit was set at around 0.5 Bq/m2 both for plutonium 238 and plutonium 239+240.
- Deposition density, error and detection limit at time of measurement.
- "ND" in the column "Deposition density", "-" in the column "Error", and detection limit value as reference in the column "detection limit": The peak of relevant nuclide was not clearly detected or calculated deposition was equal to or below 0.0.
- Reference value in the column "Deposition density" smaller than the detection limit in the column "detection limit": The peak of the relevant nuclide was detected even though the calculated deposition was below detection limit.
