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Radioactively-hot Particles Detected in Dusts and Soils from Northern Japan by Combination of Gamma Spectrometry, Autoradiography, and SEM/EDS Analysis and Implications in Radiation Risk Assessment

Authors:

Dr. Marco Kaltofen – Nuclear Science and Engineering Program, Dept. of Physics, Worcester Polytechnic Institute

Arnie Gundersen – Chief Engineer, Fairewinds Energy Education, Community Research Fellow University of Vermont 

Complete Methodology: 

The purposes of the study were to identify and collect samples with a high potential to contain radioactively-hot particles for microscopic examination, to determine if local hot spots of contamination existed at the time of the Fukushima Dai-ichi meltdowns, and finally to document whether any hot spots persisted five years after the accidents.

Samples of 180 Japanese house dusts, car engine filters, HVAC filters, street dusts and fine surface soils were collected and shipped to Worcester Polytechnic Institute for radioisotope analysis. A total of 235 US and Canadian samples of similar matrices were collected between 2011 and 2015. Of these 180 Japanese particulate matter samples, 57 were automobile or home air filters, 59 were surface dust samples, 29 were street dusts (accumulated surface soils and dusts) and 33 were vacuum cleaner bag or other dust samples. All filters were in service on or after March 11, 2011, the date of the initial releases from the Fukushima Dai-ichi reactors.

Of the 180 samples from Japan, 108 were collected in Japan during 2016 while the remaining 72 samples were collected during 2011. These samples included fine surface soils, sediments from drainage areas, and soils from floor mats. Dusts were collected from bulk and surface dust accumulations; including air handling fans, residential air filters, vacuum cleaner bags, automobile air filters, public restroom ventilation fans and from surfaces at public transportation points throughout northern Japan. This study used a mix of samples submitted by volunteers and by the authors. There were controls on the volunteers’ methods used to select samples, however direct sampling oversight was limited. Fifteen scientists and volunteer citizen-scientists collected these samples in areas across Japan, but predominantly in Fukushima Prefecture and Minamisoma City. Sampling locations were in publicly-accessible areas such as bike paths, roadways, sidewalks and public buildings. Permits were received to sample in restricted areas where post-Fukushima meltdown decontamination work was in progress. A majority of these samples were collected from locations in decontaminated zones cleared for habitation by the National Government of Japan.

Sample collection

Sample collection was biased by performing a preliminary visual survey to facilitate collection from areas where fine particulate matter can accumulate, such as low spots on roads or rooftops, air handling fan blades, floor mats and rooftops. For the 2016 sample set (108 of 180 samples), an International Medcom Inspector Alert surface contamination monitor (radiation survey meter) was used to identify samples from within low lying areas and on contaminated outdoor surfaces. Screening introduces a bias to the soil sample set allowing for maximum probability of collecting particulate matter that might contain hot particles. Indoor dusts, HVAC system dusts and auto air filters were randomly selected and no survey meters were used nor were surface radiation measurements taken prior to dust sample collection.

At the time of the 2016 sampling campaign, mapped surface activity data was available from Safecast, an open citizen-led group that collected activity data via a standardized device of their own design, the bGeigie. Uncontaminated areas in Japan (as mapped by safecast.org) have bGeigie-measured activities on the order of 0.08 uSv/hr. or less. Areas of known contamination are on the order of 0.16 uSv/hr. and higher. More than 90 percent of the samples in this study come from the areas Safecast-mapped as 0.16 uSv/hr. and higher (Figure 1). This indicates that the data are more representative of the contaminated zone, rather than of Japan as a whole. Mapping via the Safecast bGeigie proceeds with a plastic alpha and beta shield around the detector element. This makes the device essentially a gamma activity monitor. Thirteen of the 2016 samples from Japan were measured by the primary instrument (Ortec NaI well gamma photon detector) and the bGeigie. With the shield present on the bGeigie so that both devices measured gamma energy only, the R2 value between the two sets was 0.97, a good fit (Figure 2). Without the shield the bGeigie also accumulated beta and alpha energy, so the fit was poorer, with R2 = 0.15. The strong correlation between the bGeigie in gamma mode and the Ortec spectrometer is added evidence that the sampling methodology provides data that is more representative of the contaminated areas in northern Japan, and less so for Japan as a whole.

For each 2016 sample collection location point, a photograph was taken to provide an image of where the sample was collected as well as a record of the GPS location. All Japanese samples were air dried at ambient temperature prior to analysis, then shipped internationally to Worcester Polytechnic Institute in Worcester, MA, USA, for analysis.

Motor vehicle engine air filters process large volumes of air. In Japan private vehicles average 65 liters of gasoline use per month. (Schipper 2009) This fuel requires approximately 638 cubic meters of air for complete combustion. This is about 30 cubic meters per day, which is in the same order of magnitude as a working adult tidal air volume of 10 to 20 cubic meters per day. It was hypothesized that engine air filters in routine use and first installed prior to March 11, 2011 would provide an approximation of the amount of radioactive dusts present in ambient air for each driving region.

Bulk dust and street dust/soil samples were air dried at ambient temperatures prior to analyses. Dust samples containing macroscopic objects and excessive pet hair were sieved to pass a 150 micron brass ASTM #100 screen. Samples were divided and separately screened by gamma spectroscopy to determine if activity was heterogeneously distributed within samples. Samples were sequentially divided if necessary, based on gamma-screening results.

Dust was mechanically removed from automobile and HVAC filters. Motor vehicle air filters varied in usage from nearly new to as much as 55,000 logged kilometers of use. Sample results for dust samples were reported on a kBq kg-1 basis. Eight filter samples with detectable activities but with dust that could not be quantitatively removed from filter media were assigned a dust mass of 1.0 g. This introduced a low bias to these samples. Nine samples had activities greater than 0.25 MBq kg-1. To ensure safe transport, these samples were mass-limited to 3 grams before shipping from Japan.

Included in this set of nine atypically-radioactive samples, was a 300 mg sample of street dust received from a location about 10 km from the Fukushima-Dai-ichi accident site in Namie-machi, Futaba-gun, Fukushima Prefecture. This is in the restricted zone, close to but just outside of the exclusion zone. A very similar sample was collected from Iitate. The particulate matter samples were analyzed by sodium iodide gamma spectrometry. One vacuum bag received from a home in Nagoya, Japan, yielded subsamples with no detectable radioactivity above background, despite a sizable amount of activity for the bag as a whole. (Nagoya is 433 km from Fukushima Dai-ichi). By sample division and hot particle isolation with a pancake detector, a single 1 cm by 2 cm glass slide was prepared, with a small number of microscopic dust particles (with activity > 1 MBq ug-1) mounted via double sided adhesive tape.

Analyses of the samples proceeded sequentially by NaI gamma spectrometry, autoradiography of high activity samples, and scanning electron microscopy / energy dispersive X-ray analysis (SEM/EDS) of individual radioactively-hot particles identified by autoradiography (Moody 2015). Autoradiographs were prepared from the highest specific activity samples using blue-sensitive X-ray film, followed by SEM/EDS analysis of autoradiographically positive portions of the sample. Air filter media that had positive gamma spectrometry results were mounted in a single layer onto double sided adhesive paper sheets. These sheets with dusts were then attached to 3 mm thick copper plates. Vehicle and HVAC air filters were prepared by cutting the filter media from their frames, and mounting the filter media on 3 mm thick copper plates. A sheet of blue-sensitive Xray film was sandwiched with the mounted filters, and exposed in a dark photographer’s box for seven days. The autoradiographs used MidSci® classic blue autoradiography film BX and D76 processing.

All gamma spectrometry data are corrected for geometry, and were standardized against a known activity of 137Cs. Gamma photon analyses used Ortec® NaI and Canberra® GeLi flat plate photon detectors. An Ortec® NaI well detector and 1K MCA were also used. Counting efficiency @ 662 keV was found to be 30% based on use of a certified calibration standard from an Eckert & Ziegler Isotope Products standard source, manufactured and certified on Sept. 12, 2011, with 40.12 nCi of 137Cs. The 137Cs in the standard used for quantitation and any Fukushima-related 137Cs in the samples were of the same approximate age, therefore no 137Cs decay correction is warranted in this five-year study. Nuclides not amenable to gamma spectrometry, such as strontium, were not analyzed in this study.

Samples with evident gamma spectral peaks for uranium, thorium or plutonium were selected for SEM/EDS analyses. All particles were mounted as a monolayer on a 25 mm OD Ted Pella, Inc., PELCO® tape tab-covered aluminum SEM stub. If necessary to improve particle conductivity, the samples were carbon or gold coated prior to SEM/EDS analysis. SEM/EDS work was tested commercially at Microvision Laboratories of Chelmsford, MA, using a Bruker® X-Flash® Peltier-cooled silicon drift detector (SDD). The electron beam current was 0.60 nAmperes, accelerated at a voltage of < 0.5 to 60 keV.


Want to look at the numbers? Click below to download the complete data sheet of our samples (.xlsx). 

Activities as radio-cesium

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Maps of Safecast data and sample sites in Japan

july 27 2017 2.jpgAbove-left) Safecast map with dark blues representing low contamination

(Above-right) Map of study sample areas using same Safecast color scheme

Boat tracks and other clutter have been removed from this graphic.

Japan Radiation Interactive Map

https://www.google.com/maps/d/viewer?mid=1SisuJIoEisdEcdieMsml2iT_pJk&ll=38.477934360996386%2C135.87120000000004&z=6

(Above) Browse the location, supplementary info and photographs of samples taken in Japan with our interactive sample map created by Ben Shulman-Reed, Fairewinds Energy Education program researcher. 

Safecast bGeigie data vs. Ortec NaI gamma spectroscopy data

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Japanese dusts and sediments presented by specific activity in kBq kg-1

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Distribution of total radiocesium activities in particulate matter samples from Japan

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Gamma spec Ibaraki Prefecture, analyzed April 11, 2011

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Tokyo vehicle air filter image (Left) and 7 day exposure autoradiograph (Right) Corresponding auto exposed points on the X-ray film are connected by red lines.

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SEM image of hot particle, magnification 5000 X.

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(Top) SEM/EDS spectrum showing one nodule of hot particle with 15.6% Cs, 16.7% Te, 1.2% Rb, 0.61% Po.  (Bottom) second nodule with 48% Te, 1.2% Po, 0.18% Dy (analyzed 12/18/2013).

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To read more at :

http://www.fairewinds.org/stoten-methods/

http://www.sciencedirect.com/science/article/pii/S0048969717317953

July 27, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

East Japan Soil Measurement Project of Minna no Data, Dec.2015 to Sept. 2016

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Source: http://www.minnanods.net/soil/pref17_colored/map17.html

September 26, 2016 Posted by | Fukushima 2016 | , , | Leave a comment

East Japan Soil Measurement Project of Minna no Data Site

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About This Project

It’s time to cooperate

When we started up MDS (Minna no Data Site, Everyone’s Data Site) we constructed inclusive and shared system on measuring data of food as the first stage, as there were many people who were concerned about food intake.

However, we planned to launch the measuring data of soil as a second stage after intensively equipped the system on food.

In autumn 2014, after one year from opening of MDS, we start up to platform soil measurement data. We, as citizens, try to start to map the status of soil contamination spread over East Japan.

The following is the reason why we stand up to start the East Japan Soil Becquerel Measurement Project. Objectives, outline and methodology of the project is explained.

Outline

In the Project, the method of collection is standardized in order to make comparison of data from multiple measurement laboratories. The Manual for Collection is developed by considering the easiest method of measurement within the limits of keeping accuracy, because many citizens conduct collection and measurement by themselves.

Collected soil is measured by the participating measuring laboratories of MDS. The result becomes open to the public and the report is sent to the collector.

Objectives

Radioactivity contamination by the accident of Tepko Fukushima Nuclear Power Plant is long term lasting.
The soil contamination map of broader areas is needed to understand contamination of neighborhood by measurement and comparison of data.

Though central and local governments conduct soil researches, those researches are insufficient because the value is lower by measuring deep place, or they measure only air dose.
As they decide the spot of measurement by mesh, the data what citizens want to know is lacking.

In our Project, we aim to grasp status of contamination where citizens make living every day. For example, place where children frequently play, where people pick wild grass, or where farmers work is being measured.

The Project aims that people can access necessary information as much as possible by utilizing data and database and by accumulating information which one can find at a glance and can search at ease.
We hope the result would be used as a tool for action for everyone.

Methodology

The depth of collection is from 0 to 5 cm, because most of cesium stays within 5 cm from surface of the earth.

Collection of soil should be conducted when it does not rain for several days, in order to avoid weight error caused by water. Less than 10 percent of moisture content is desirable.

Spot for collection is set at higher dose spot by measuring rate of air dose (1m5cm).
The extreme high spot such as micro hot spots and concentrated environment are excluded.

Collection is made by a method to compare results of each place.

Samples are measured at the participating laboratories of MDS.

  ・Measurement accuracy of those laboratories is ensured by the MDS original examination.

  ・The results are accumulated in the common database.

The result sof measurement are open to public on MDS. MDS has Japanese and English site.

Mapping of data is planned after gathering enough results.

Trial calculation of amount of radioactivity by a square meter is planned to be conducted. (Becquerel/ Kg →Becquerel /square meter)

Target areas17prefectures in east-Japan

Tohoku : Aomori Iwate Akita Miyagi Yamagata Fukushima

Kanto : Ibaragi Tochigi Gunma Saitama Chiba Tokyo Kanagawa

Chubu : Yamanashi Nagano Shizuoka Nigata

* In Iwate, the Soil Project Iwate had implemented measurement at more than 300 spots in 2012 and 2013.

The project activity will be made starting from requested districts. Individuals, groups and any organization such as school and daycare can participate in measurement of proposed spots. Proposing more than 5 spots are desirable.
The measurement spots will be decided after consultation basically in the same municipality.

How to support us: 
Collection of samples, payment of 2,000yen for measurement of one sample, payment of actual postage for samples.

How to feed back :
Sending result of measurement of the spots including spectrum, Reading and downloading data at MDS.

Support our site and project!
To those of you who are viewing this site from overseas, Thank you for visiting ”Minna no Data Site” (Combined Database of Independent Radioactivity Measurement Labs) .

MDS has stacked the data measured by the independent radioactivity measurement laboratories in response to the Fukushima Daiichi nuclear power plant accident, As of September 2014, the number of the food data became nearly 10,000.

For the benefit of those who worry about radioactive contamination of Japan from overseas, we opened the English site. We have started “East Japan soil measurement project” since October 2014 in addition to the food data.

From the fact that government has not done the adequate soil contamination survey for the citizens, this project promotes measuring soils of the places like parks, vacant lots, and educational facilities which are closely related to children’s daily life.

This project is based on the method of “Iwate soil measurement project “(2012- 2013) by citizens of Iwate Prefecture. If the method for collecting the soil is different, the results of monitoring vary greatly.

By using an easy-to-understand manual of the standardized method, you are able to compare, review and analysis the data from different locations. We will publish the measurement results of soil on this site.


We record the status of the radioactive contamination of Japan carefully from the standpoint of citizens, and hope that it will help people who are living with anxiety. For the people overseas, we are preparing the English version of data to show where and how much radioactively contaminated.

To run this project, big budget for measurement cost and update cost of web systems are required. There are 300 locations in each 17 prefectures in Eastern Japan, and each place costs about 4,000 yen.
Although it is planned to reduce costs and to ask for volunteers as much as possible, still the costs such as measurement costs, project management costs and Web systems costs are expected to some extent also.

It is a project of the scale that no one even challenged yet. We rely on your generosity to help funding for this project. We would appreciate your support from abroad. Thank you for your cooperation and support.


The information page of “East Japan soil measurement project” is currently in preparation. It will be published shortly.

◎Donate by the bank transfer
Postal Transfer:
Postal Transfer Account : 10090-85754261
Account Name: Minna no data site Unei Iinkai

Bank Account
Yuucho Bank Branch : Zero Zero Eight (Branch 008):
Interim : 8575426
Account Name: Minna no data site Unei Iinkai

Remittances in either USD or EUR can be made from overseas banks,.  
Please note that remittances to Japan cannot be made from certain financial institutions.
For details, please ask your local bank.

http://en.minnanods.net/#mds_indx_srch

http://en.minnanods.net/soil/soil_support.html

http://en.minnanods.net/support/supportourproject.html

Japanese Site

Contact

September 26, 2016 Posted by | Fukushima 2016 | , , , , | Leave a comment