Period of the Project
Oct. 2014 to Sep. 2017
Free measurements took place from the start of the project
to the end of January 2017. Since then, measurement laboratories
have been charging a flat fee of 2,000 yen (about
$18 USD) per measurement.
17 Prefectures in Eastern Japan
Aomori, Iwate*, Akita, Miyagi, Yamagata, Fukushima, Ibaraki, Tochigi, Gunma, Saitama, Chiba, Tokyo, Kanagawa, Yamanashi, Nagano, Shizuoka, Niigata. (Iwate Prefecture measurements began in 2012 by a group called “Soil Research Project Iwate”)
Background of this Project
What prompted Minna-no Data Site to initiate this laborintensive project? It is not as if there was no data issued by the government and other authorities, which measured the quantity of becquerels in the soil using a standardized process.
However, most of this data was not useful to citizens because of the way it was collected. For example, much of the data came from limited areas, such as one sample taken every several kilometers. In addition farm soil samples were taken at a depth of 15 cm, which does not show the contamination at the surface of the ground. Furthermore, much of the data was merely estimated using a formula which referenced air dose rates measured by airplane.
Citizens wanted answers to questions such as “Where is it safe for our children to play?” or “What is the actual level of contamination around our homes?” The lack of answers to these questions made many people uneasy, and led to the decision to carry out the “East Japan Soil Becquerel Measurement Project” while it was still possible to detect Cs-134, which has a relatively short half-life. By doing so, we were able to determine the amount of contamination brought about
by the Fukushima Daiichi NPP accident.
Soil Research Project Iwate as a Model Project
When initiating the “East Japan Soil Becquerel Measurement Project”, Data Site referenced research which had been extensively
conducted by “Soil Research Project Iwate” from 2012 to 2013 in Iwate Prefecture.
In this project, a laboratory based in Nagoya called C-Labo, and a citizens’ group based in Iwate called “Protect Children from Radiation Exposure Iwate” planned and promoted the project together with the cooperation of three citizens’
measurement laboratories, “SAVE CHILD iwate”* from Iwate Prefecture, “Kanegasaki” from Iwate Prefecture, and “Chiisaki Hana” from Miyagi Prefecture.
The aim of the project was to get at least one sample from each and every municipality in Iwate Prefecture. The mothers involved in the project chose locations which were of concern to them, such as parks in the southern part of the prefecture, and in total they carried out soil measurements in three hundred sixteen different locations. In the end, they compiled a color-coded map which was entitled “Radiation Contamination Map of All Iwate Prefecture”
*“SAVE CHILD iwate” withdrew from Data Site in May 2018.
Standardizing the Sampling Method became the Key to Success
Before the start of the “East Japan Soil Measurement Project”, citizens brought in many soil samples, and the various participating laboratories carried out numerous measurements.
However, it soon became apparent that the soil samples had been taken from different depths, and that details about where the samples were taken from were not necessarily clear. For this reason, it was not possible to widely compare the results with each other.
With the start of the project we insisted on standardizing the sampling method, and by doing so it became possible to obtain valid data which could be compared with the data collected by MEXT (Japanese Ministry of Education, Culture, Sports, Science and Technology) or data which had been collected after the Chernobyl nuclear accident. Thus, only soil samples taken using the following standardized method were admitted as part of the project sample.
Our Standardized method to collect the project sample.
(1) How to Select a Sampling Spot
If you have an air dosimeter, check the air dose of the surrounding area. Avoid hotspots, where
the air dose is extremely high, and select a sampling point where the soil has not been replaced,
covered, or cleaned.
(2) Be Sure to Make Notes in Your “Field Notebook”
Make detailed notes about the landscape, geographical condition and surrounding environment.
When examining the data at a later date these notes will be the only clues available.
(3) Measure the Air Dose (if possible)
Measure the air dose of the sampling point at two points (5 cm above ground and 1m above ground) and record this data in your field notebook
along with the model type of your air dosimeter.
Obey the Unified Sampling Depth of 5 cm
(4) Take the surface soil at a depth of exactly 5 cm, and collect slightly
more than 1 liter of soil. This is the same depth used in samples in Chernobyl and by MEXT. You will get a higher figure if you take only highly contaminated surface soil, whereas if you take deeper uncontaminated
soil the figure will be relatively lower. After collecting the soil, place it inside two plastic
bags and insert a ‘control slip’ with the sampling location written on it in between the two bags.
(5) Sift and Dry the Soil before Measurement
Before measuring the soil, either the person taking the sample or someone at the measurement laboratory
must sift and dry the soil to remove any impurities.
Ensuring Everyone Takes Accurate Samples
When seeking the assistance of average citizens, we published and made available the following tools so that everyone collected soil in the same manner, and from suitable spots.
- Sampling manual complete with photos
- Comic book version of the sampling manual, complete with questions and answers
- Video showing the correct sampling method
- Courses (held over one hundred times in various locations) to explain the sampling method
Working to Improve the Accuracy of Soil Measurement
Most of the citizen measurement laboratories use NaI Scintillation Detectors (using Sodium Iodine).
When using this type of detector, depending on the make of the detector, the measurement results can be affected if there are low levels of radioactive cesium and high levels of naturally present radioactive materials. Therefore, for the implementation of this project we developed and implemented an accuracy control method in order to ensure the accuracy of the soil measurements.
First, a test sample was prepared by mixing together contaminated soil from Fukushima Prefecture with uncontaminated soil from the
Chugoku Region of southern Japan which contains high amounts of natural radioactive materials such as uranium, thorium, and their daughter radionuclides. Then this test sample soil was measured using all of the detectors and the measurement data was analyzed so as to determine a method to judge whether or not the natural radioactive materials were intervening in the measurement results. Over the course of a year the judgement criteria for when to carry out data correction was established with the goal of publishing more accurate
How to Deal with Hotspots
In the project, hotspots were excluded from the collection target in order to compare the relative contamination of each area on the map.
On the other hand, interspersed hotspots from various places could not be ignored.
So, a sub-project entitled “Environmentally Concentrated Becquerel Measurement Project” was established and we requested the assistance of a citizen’s group called “Hotspot Investigators for Truth” (HIT) to carry out hotspot measurements.
The results of this project have been categorized into twelve different patterns of hotspots and the actual measurement results have been published on our website: