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The News That Matters about the Nuclear Industry Fukushima Chernobyl Mayak Three Mile Island Atomic Testing Radiation Isotope

May 7 Energy News

geoharvey

Opinion:

¶ “Long Island’s energy future may be blowin’ in the wind” • Earlier this year, final agreement was reached between the Long Island Power Authority and Deepwater Wind, which had developed the Block Island offshore wind farm, to provide power to Long Island’s South Fork. It is one more in a series of developments. [Newsday]

Block Island (Photo: AllIslandAerial | Kevin P Coughlin)

¶ “Noah Smith: Climate skeptics always assume risks are overhyped” • Bret Stephens of the New York Times made a splash with a column questioning the scientific consensus on climate change. He didn’t cite any skeptical research papers or alternative theories. His doubt was based purely on distrust of scientific consensus. [WatertownDailyTimes.com]

Science and Technology:

¶ The amount of dissolved oxygen in the water of the world’s oceans, an important marker of overall oceanic biological health/livability, has been declining at a notable…

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May 7, 2017 Posted by | Uncategorized | Leave a comment

Anthropogenic noise pollution is threatening wild spaces

GarryRogers Nature Conservation

GR: Earth’s wildlife decline is caused by construction, invasive species, climate change, and many other human impacts. For instance, scientists have shown that the sounds coming from our industry, airplanes, cars, and even our voices are harmful. The story below reports the results of a new study of the effects of sound on wildlife.

“Wild spaces are important for many reasons. For us humans, they give us peace and energy, provide places for recreation and connection with nature, and teach us about the life around us. But wild places are not only necessary for humans – for flora and fauna and the land itself, protected areas are reserves where nature can run its course without as much interference from humans. They provide critical places for the earth to heal itself and resume its organic processes; they also give homes to many endangered species. Yet unfortunately, protected areas may not…

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May 7, 2017 Posted by | Uncategorized | Leave a comment

May 6 Energy News

geoharvey

Opinion:

¶ “Rising Tides Will Create The World’s Next Refugee Crisis” • Experts say climate change poses the greatest security threat and mass displacements will soon be normal. With human-caused climate change, sea levels will rise, storms will grow stronger, floods more violent, and draughts harsher, increasing risk to human beings. [Huffington Post Canada]

Brooklyn, the morning after Hurricane Sandy’s landfall.

¶ “Missing EPA Webpage Could Be Violation of Federal Law” • When EPA’s climate change pages were shuttered for revisions reflecting the administration’s views, users are told they can check out a snapshot of the entire EPA site from the day before Trump took office. But in the archived snapshot, pages relating to climate change are missing. [Seeker]

Science and Technology:

¶ Decades of increasing temperatures in Alaska have lengthened the fire season and dried out vegetation, especially in the forest floor, and created conditions for…

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May 7, 2017 Posted by | Uncategorized | Leave a comment

Firefighters faced with wildfire in radioactive area near Fukushima Nuclear Power Plant

FukushimaFire.jpgAbove: wildfire near the Fukushima Nuclear Power Plant. Screengrab from KYODO News video.

 

Firefighters are struggling to contain a wildfire in an area that is contaminated with radiation near the Fukushima Nuclear Power Plant that melted down after the 2011 earthquake and tsunami off the coast of Japan (map).

The blaze, estimated at about 50 acres, started April 29 near the town of Namie. The video below shows helicopters dropping water on the fire.

 

http://wildfiretoday.com/2017/05/06/firefighters-faced-with-wildfire-in-radioactive-area-near-fukushima-nuclear-power-plant/

May 7, 2017 Posted by | Fukushima 2017 | , , | 1 Comment

Group creates film and story series based on interviews with Fukushima evacuees

n-fukushima-a-20170506-870x580.jpgHidenobu Fukumoto (right), head of a group that produces picture-story shows, visits the home of Yoko Oka in Namie, Fukushima Prefecture, in January. Namie was a restricted zone until the government lifted an evacuation order in March.

 

Six years ago in March, a firefighter in the town of Namie in Fukushima Prefecture couldn’t save tsunami victims in the wake of the Great East Japan Earthquake, because he himself had to evacuate due to the nuclear crisis at the Fukushima No. 1 power plant.

His anguish has been illustrated in the animated film “Munen” (“Remorse”), which was shown in France at Maison du Japon of Cite Internationale Universitaire de Paris on March 25 this year following screenings at various places in Japan.

The film begins with a scene in which the wife of the firefighter explains to her niece why her husband puts his hands together everyday and looks toward Namie.

He is apologizing to lives that he could not save,” she tells her niece.

At the screening in Paris, the audience of about 100 people stared at the screen. The crowd erupted in applause when the film ended.

France depends heavily on nuclear power, which produces 75 percent of its electricity.

I could understand clearly the seriousness (of nuclear power). I want many French people to watch this,” said a male university professor.

A citizens’ group that created the film has also produced about 40 illustrated story performances in the last five years, featuring experiences of evacuees of the nuclear disaster and a folk tale set in areas that have emptied of people. The shows have also been screened at various locations.

One story called “Mienai Kumo no Shita de” (“Under the Unseen Cloud”) depicts the life of a female evacuee from Namie.

Another called “Yuki-kun no Tegami” (“Yuki’s Letter”) features an autistic boy who struggles in an evacuation center, while a work titled “Inochi no Tsugi ni Taisetsuna Mono” (“The Precious Thing Next to Life”) is based on a story from the disaster that a manager of an inn heard from a fisherman.

Munen” was also based on an illustrated story.

An illustrated story show is easy and inexpensive (to produce). It tends to win the sympathy of the audience as it stimulates their imagination,” said Hidenobu Fukumoto, who heads a group called Machi Monogatari Seisaku Iinkai (Town Story Production Committee).

The 60-year-old former official of the Hiroshima Municipal Government was born in Hiroshima and graduated from Hiroshima Shudo University.

At the city office, he was involved in publishing a public relations magazine and event planning, with many opportunities to create illustrations. He retired in March.

What prompted him to create the shows was a book about the relationship of the atomic bombing of Hiroshima and the nuclear plant in Fukushima operated by Tokyo Electric Power Company Holdings Inc. He read the book when he was engaged in volunteer activities in Fukushima after the disaster.

The book by Hisato Nakajima, titled “Sengoshi no Nakano Fukushima Genpatsu” (“The Fukushima Nuclear Power plant in Postwar History”), includes the story of a Tepco employee who was involved in the construction of the Fukushima No. 1 power plant.

The man, who lost his older brother in to the atomic bombing, also helped rescue atomic bomb survivors. In around 1964, he was assigned to work in the town of Okuma in Fukushima and talked to local people who were concerned about hosting a nuclear plant.

I saw the B-29 bomber that dropped the atomic bomb and the mushroom cloud that soared in the sky afterward. I know the fear more than you all do, and that’s why I studied nuclear power seriously,” the man is quoted as saying. “I believe nuclear power is safe enough, as it is put under extremely thorough safety measures.”

Fukumoto was shocked to learn that the man’s atomic bombing experience was used to convince people to accept the construction of a nuclear power facility.

Meanwhile, the book also tells about a landowner in Namie — where Tohoku Electric Power Co. had planned to build a nuclear power facility — refusing to sell his land because he witnessed the devastation following the atomic bombing of Hiroshima.

In the 1960s when I was in elementary school, atomic bomb survivors in Hiroshima refrained from talking about the bombing over fear of being discriminated against,” Fukumoto said.

If the horror of the atomic bombing had been conveyed better, people in Fukushima might have become suspicious about being persuaded, and nuclear power plants would not have been built,” he said, adding that if Fukushima becomes silent, the silence could be used as an excuse for maintaining nuclear power.

In order to prevent that outcome, Fukumoto is determined to convey the stories of remorse triggered by the meltdown disaster, the stories of evacuees, and the individual personalities of the victims.

Every month, Fukumoto makes a round trip of around 800 kilometers between Hiroshima and Fukushima to hold interviews to create new stories.

On Jan. 31, he visited the Namie home of 56-year-old Yoko Oka. Oka evacuated to the city of Fukushima, as her home was in a restricted zone which allowed only daytime access. The restriction was lifted at the end of March this year.

Her home was almost empty after she threw away everything but a chest, which she brought after getting married. There were many holes in the paper doors because they were devastated by masked palm civets, which also scattered feces in the home.

Oka stood in front of a pillar marked with the heights of her two daughters.

This is the only proof that we lived here,” she said.

Fukumoto listened carefully to Oka and photographed her. Based on such interviews, he uses his computer to make illustrations for new stories and write scripts.

The production group currently has around 10 members, including a hibakusha from 72 years ago. The survivor continues to contact Fukushima evacuees, believing it is not someone else’s problem as they both were exposed to radiation.

There are also many evacuees who perform similar shows in various places.

Hisai Yashima, 51, who evacuated to the town of Kori, Fukushima, belongs to a group of around 15 storytellers.

I could not have talked about (the nuclear disaster) if I were in my 20s … waiting to get married or expecting a baby,” she said. “Our generation can talk about it and young generations can succeed after they get older.”

After hearing the experiences of those who survived the atomic bomb in Hiroshima, Yashima thought the prejudice echoes the discrimination suffered by the Fukushima nuclear disaster evacuees.

But she is proud that the group was able to visit some 500 locations to screen shows.

We are able to send out (our message). We will never let people become silent like in Hiroshima,” Yashima said.

http://www.japantimes.co.jp/news/2017/05/06/national/group-creates-film-story-series-based-interviews-fukushima-evacuees/#.WQ7pomG-ihB

 

May 7, 2017 Posted by | Fukushima 2017 | , | Leave a comment

First On-Site True Gamma-Ray Imaging-Spectroscopy of Contamination near Fukushima Plant

Abstract

We have developed an Electron Tracking Compton Camera (ETCC), which provides a well-defined Point Spread Function (PSF) by reconstructing a direction of each gamma as a point and realizes simultaneous measurement of brightness and spectrum of MeV gamma-rays for the first time. Here, we present the results of our on-site pilot gamma-imaging-spectroscopy with ETCC at three contaminated locations in the vicinity of the Fukushima Daiichi Nuclear Power Plants in Japan in 2014. The obtained distribution of brightness (or emissivity) with remote-sensing observations is unambiguously converted into the dose distribution. We confirm that the dose distribution is consistent with the one taken by conventional mapping measurements with a dosimeter physically placed at each grid point. Furthermore, its imaging spectroscopy, boosted by Compton-edge-free spectra, reveals complex radioactive features in a quantitative manner around each individual target point in the background-dominated environment. Notably, we successfully identify a “micro hot spot” of residual caesium contamination even in an already decontaminated area. These results show that the ETCC performs exactly as the geometrical optics predicts, demonstrates its versatility in the field radiation measurement, and reveals potentials for application in many fields, including the nuclear industry, medical field, and astronomy.

Introduction

Following the accident in Fukushima Daiichi Nuclear Power Plants on 11 March 2011, a huge amount of radionuclides was released to the atmosphere. As in 2016, 137Cs and 134Cs, which radiate gammas mainly from 600 keV to 800 keV, still remain in Fukushima, and many areas are still contaminated as a result1. Operations of decontamination are called for in a wide area in Fukushima and its surroundings to satisfy a legal limit for the maximum exposure of 0.23 μSv/h at any publicly-accessible open spaces2. An effective method to measure and monitor gamma-ray radiation is essential for efficient decontamination work, and as a result there has been a surge of demand for gamma-ray instruments with a wide field of view (FoV) which quantitatively visualize Cs contamination.

Many gamma cameras have been developed to make imaging observations to help decontamination, based on the Compton camera (CC)3,4,5,6,7, pin-hole (PHC)8, and coded-mask technologies. However, none of them has detected more than a limited number of hot spots, or has reported any quantitative radiation maps, let alone imaging spectroscopy. The CC is the most advanced among these three, yet has an intrinsic difficulty in imaging spectroscopy, which is related to its Point Spread Function (PSF)9,10.

So far, the most successful evaluations for the environmental radiation in contamination areas have been made by backpacks11 and unmanned helicopters12,13. Although these methods are, unlike gamma cameras, non-imaging measurements, in which measurements at each point are made with either a spectrometer or conventional dosimeter, quantitative and reliable 2-dimensional distributions of radiation have been successfully obtained after several measurements with overlapping fields of view are combined. The downside is that they require a considerable amount of time and efforts, and thus are not practical to be employed in a wide area.

Another fundamental problem with all these methods is that they do not directly measure the radioactivity on the ground, but measure the dose at 1 metre high from the ground (hereafter referred to as “1-m dose”) instead, and hence require complex analyses to convert the measured dose to the actual radioactivity on the ground. Indeed, we show that the 1-m dose does not always agree well with that measured immediately above the ground, which suggests an intrinsic difficulty in obtaining an accurate radioactivity distribution on the ground from the 1-m dose.

After a few pilot experiments of decontamination were conducted in Fukushima, it turned out that the amount of reduction of the ambient dose by decontamination was limited. The reduction ratios, defined by the dose ratio compared between before and after decontamination, were approximately 20% only in lower ambient-dose areas (<3 μSv/h)2, while >39% in higher ambient-dose areas (>3 μSv/h). When a (high) dose is measured at a point, gammas that contribute to the dose can originate anywhere a few radiation lengths away (~100 m) from the point. The goal of decontamination is to somehow identify and remove those radiation sources. However, none of the existing instruments can identify them, i.e., none of them can tell where or even in which direction the radiation source is located. To untangle the sources of a dose of contamination, the directions of all the gammas, as well as their energies if possible, must be determined. It means that the brightness distribution around the point must be obtained.

To address these issues of existing methods and visualize the Cs contamination, we have developed and employed an Electron-Tracking Compton Camera (ETCC). ETCCs were originally developed to observe nuclear gammas from celestial objects in MeV astronomy14, but have been applied in wider fields, including medical imaging15 and environmental monitoring16,17. An ETCC outputs two angles of an incident gamma by measuring the direction of a recoil electron and hence provides the brightness distribution of gammas with a resolution of the PSF9,10. The PSF is determined from the angular resolutions of angular resolution measure (ARM) and scatter plane deviation (SPD)9,18. The ARM and SPD correspond to a resolution of the polar and azimuthal angles of an incident gamma, respectively. Since a leakage of gammas from their adjacent region to the measured point is correctly estimated with the PSF, quantitative evaluation of the emissivity anywhere in the FoV is attained.

The most remarkable feature of the ETCC is to resolve the Compton process completely; the ETCC does not only provide the direction of a gamma, but also enables us to distinguish correctly reconstructed gammas from those mis-reconstructed9. Thus, the ETCC makes true images of gammas based on proper geometrical optics (PGO), as well as energy spectra9 free of Compton edges10. The PGO enables us to measure precise brightness (or emissivity) at any points in an image using an equi-solid-angle projection, such as Lambert projection, without the information of the distance to the source, as shown in Fig. 1. The obtained emissivity can be unambiguously converted into the dose on the ground (hereafter the E-dose), of which the procedure is identical with that described in the IAEA report19, but without need of the fitting parameters. We find the E-dose to be consistent with the dose independently measured by a dosimeter, and thus confirm that remote-sensing imaging-spectroscopy with the ETCC perfectly reproduces the spatial distribution of radioactivity10.

gfglm.jpg

 

Results

We performed the field test of gamma measurement in October, 2014 in relatively high-dose locations with the averaged ambient dose ranging from 1 to 5 μSv/h in Fukushima prefecture, using the compact 10 cm × 10 cm × 16 cm ETCC with a FoV of ~100°ϕ17. The SPD and ARM of the ETCC were measured to be 120° and 6° (FWHM), respectively, for 662-keV 137Cs peaks, which correspond to the PSF (Θ~15°), i.e., the radius of the PSF of 15° for the region that encompasses a half of gammas emitted from a point source9. It uses GSO scintillators and has an energy resolution of 11% (FWHM) at 662 keV. We chose the three different kinds of locations for measurements: (A) decontaminated pavement surrounded with not-decontaminated bush, (B) not-decontaminated ground, and (C) decontaminated parking lot. Figure 2a,c and d show their respective photographs.

hghglkml.jpg

 

We have found that the doses at 1-m and 1-cm measured with a dosimeter do not agree with each other, as demonstrated in Fig. 2a and b in the location (C). The 1-m dose, which is practically the emissivity averaged over the adjacent region of ~10 m, is the standard in the radiation measurement, presumably because it is useful to estimate potential health effects to the human body. The 1-cm dose, on the other hand, better reflects the emissivity on the ground at each grid point, of which the size is likely to be similar to the spatial resolution of the ETCC, and hence is useful to locate radioactivity on the ground for decontamination work. For these reasons, we adopt the 1-cm dose to compare with the emissivity measured with the ETCC in this work.

Figure 3a shows the photograph of FoV, overlaid with 1-cm dose at nine points and the E-dose map by ETCC, where the brightness (equivalent to the E-dose) is defined as the count rate of reconstructed gammas per unit solid angle (here 0.014 sr), corrected for the detection efficiency including the angular dependence of the ETCC9. Figure 3b shows the energy spectrum accumulated for the entire FoV, whereas Fig. 3c–e display those accumulated for the sky, the decontaminated pavement, and the not-decontaminated bush, respectively. The E-dose at the maximum brightness in Fig. 3a is estimated to be 2.6 μSv/h, which is consistent with the average of the 1-cm dose (0.9–4.3 μSv/h) around the centre of the FoV.

ghgkjlklm.jpg

jmkmmùù.jpg

 

The spatial distribution of the E-dose is found to be consistent with that of the 1-cm dose, which was independently measured. The spectrum in Fig. 3e shows prominent peaks of direct gammas of Cs, which implies the contamination from the bush area, whereas the spectrum of the decontaminated pavement (Fig. 3d) shows much weaker Cs peaks, which implies the effect of the decontamination. The latter is dominated with low-energy scattered gammas, which emanate from inside of the ground and the adjacent areas. The spectrum of the sky (Fig. 3c) is clearly dominated with Compton-scattered gammas from Cs peaks (with the expected energy ranging from 200 to 500 keV) in the air. We should note that the spectra free of Compton scattering components enable us to make the unambiguous identification of the sources of radiation.

The results of imaging-spectroscopy in the two contrasting locations (B and C), in which no and thorough decontaminations, respectively, have been conducted, are shown in Figs 4 and 5. The exposure times are 80 min and 100 min, respectively. The ETCC gives spatially-resolved spectra, and accordingly the detailed condition of contamination at each point, similar to Fig. 3. In the contaminated location (B), although the energy spectrum of the FoV shows strong and direct gamma emission from Cs, Cs is found to be concentrated in the limited area of spot 1 (Fig. 4e), whereas little Cs is found in the other regions in the FoV (Fig. 4f). As such, imaging-spectroscopic measurement is a reliable method to unravel the state of contamination quantitatively. Even in the decontaminated location (C), both the image (Fig. 5a) and spectrum (Fig. 5f) reveal the existence of a “micro hot spot”, where some Cs remains on the ground and the spectrum has the dominant Cs peak (Fig. 5f), whereas the spectra for other regions (Fig. 5e) show that the main component is scattered low-energy gammas. Both the maps of 1-cm dose (Fig. 5a) and E-dose (Fig. 5b) show a hint of a small enhancement originating from a micro hot spot, although it is at a similar level to the fluctuation of the scattered gammas. The E-doses at the points of the maximum brightness in (B) and (C) are 5.0 and 1.3 μSv/h, respectively, which are also consistent with the 1-cm dose at the corresponding points.

gvjhkk.jpg

 

klkmmù.jpg

 

Finally, we check consistency about a couple of properties of the ETCC and conventional dose measurements. First, we plot the total gamma counts obtained with the ETCC as 1-m doses at the position of the ETCC in Fig. 6a, and confirm a good correlation. Then, we plot the correlation between the 1-cm dose measured by the dosimeter and by the ETCC (E-dose) at the locations (B) and (C) in Fig. 6b. Except ~3 points adjacent to the hot spots in (B), the discrepancy between them is limited within ± ~30%. Considering the difference in the conditions, such as the size of the measured areas (~100 cm2 for a dosimeter and ~1 m2 for ETCC) and the energy range (>150 keV for a dosimeter and 486–1000 keV for ETCC), as well as the fact that a large dispersion in the accuracy of commercial dosimeters (±several 10%) has been reported, this amount of discrepancy is more or less expected. We conclude that good consistency between them is established for the wide range of the dose (0.1–5 μSv/h), and this is another proof that the ETCC achieves the PGO. In addition, the PGO gives the brightness of the sky over the hemisphere, and we find it to be comparable with that from the ground, after the difference in their solid angles is corrected (see the bottom row in Table 1). This means that roughly a half of the 1-m dose at any points originates from the sky. It then implies that the wide-band energy balance of gammas between the ground and the sky is in equilibrium and contribute to the ambient dose, presumably because the air is thick enough to scatter most of gammas emanating from the ground. It is consistent with the fact that the spectra of the sky (Figs 3c, 4c and 5c) are dominated with Compton scattering for Cs gammas (200–500 keV). This could not have been identified without spectra free of Compton edges. Our results also explain the reason why the amount of the reduction of the ambient dose was limited to often no more than 50% after decontamination work2 had been conducted in Fukushima, it is because a significant amount of radiation still comes from the sky in equilibrium.

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Discussion

Firstly, let us convert the emissivity to the 1-cm dose, using only the brightness measured by the ETCC. Figure 1b schematically shows the dosimeter configuration for the measurement of 1-cm dose. Since the top and the upper sides of the dosimeter are shielded with tungsten (W) rubber, it detects gammas emanating from the ground to the lower hemisphere only. The count density of the gammas which pass through the plane of the dosimeter (indicated as P in Fig. 1b) is estimated to be approximately 2πΣ · (1 − cos(θ = 80°)) = 5.2Σ, where Σ is emissivity on the ground. Then we convert the count density of gammas at the dosimeter position into doses in units of μSv/h with the conversion factor of 1 μSv/h = ~100 counts · sec−1 · cm−2 for 662-keV gammas in the dosimeter, based on the IAEA report19 (in page 85).

In the not-decontaminated location (B), 135 gammas were observed with the ETCC (dB) at the maximum brightness point in Fig. 4a, where the unit solid angle is 0.014 sr. The brightness of the gamma is calculated to be 135 counts · sec−1/(0.014 sr · 100 cm2) = 96 counts · sec−1 · sr−1 · cm−2, and then we get, from the relation Σ = dB, 5.2Σ = 500 counts · sec−1 · cm−2, which corresponds to the dose of 5.0 μSv/h (the two points indicated as 5.0 and 5.7 [μSv/h] in Fig. 4a). For the location (C), 35 gammas were observed at the maximum brightness point in Fig. 5a, and then dB (=Σ) = 35 counts · sec−1/(0.014 sr · 100 cm2) = 25 counts · sec−1 · sr−1 · cm−2 and 5.2Σ = 130 counts · sec−1 · cm−2, which corresponds to 1.3 μSv/h. The 1-cm dose at this point is found to be roughly equal to the average of 1.0–2.2 μSv/h in Fig. 5a. For the location (A), dB is calculated in the similar manner to be dB = 70 counts · sec−1/(0.014 sr · 100 cm2) = 50 counts · sec−1 · sr−1 · cm−2 and 5.2Σ = 260 counts · sec−1 · cm−2, which corresponds to the dose of 2.6 μSv/h. The 1-cm dose at this point is ~3 μSv/h, and is roughly equal to the average of 1–4.3 μSv/h in Fig. 3a.

For comparison, we also applied the simple method described in pages 96–101 in the IAEA report19, calculating the doses with a conversion coefficient of 8.7 × 10−3 (μSv/h)/(Bq/cm2) for θ~80° for the 1-cm dose, which is estimated by accumulating gamma-flux at each point from the ground with the tungsten rubber shield. This method is the one described in pages 96–101 in the IAEA report19. For the location (A), a gamma flux on the ground is calculated to be 2πΣ/0.85 = 369 (Bq/cm2) and then the dose is 369 × 8.7 × 10−3 = 3.1 μSv/h. For the locations (B) and (C), the doses are estimated to be 5.9 and 1.6 μSv/h, respectively. Thus, we confirmed that the results deduced by the two independent methods are consistent with each other.

Decontamination work in Fukushima faces serious difficulty; it is hard to pin down which region is badly contaminated from which radiation source without investing massive resources like wide-scale backpack measurements. The capability of the ETCC to measure the emissivity (or dose) independently of the distance would enable us to propose a novel approach to it. If a mapping of the brightness of 137Cs on the ground was carried out over the wide area with the ETCC by aircraft with the similar way conducted in 20122, we could visualize variation of the doses across the area, and could tell where decontamination work would be required most and how much.

As a different application, if multiple ETCCs are installed at various places in a nuclear plant to carry out a continuous three-dimensional brightness monitoring, we could not only detect, for example, a sudden radiation release by accident, but also make a quantitative assessment of where and how the release has happened. This would provide vital initial parameters to computer simulations to estimate the later dissemination of radioactivity over a wide area after an accident. In fact, simulations for this purpose faced a great difficulty in the past due to lack of reliable observed parameters of radio activity, because radiation monitoring was performed solely by repeated simple dose measurements. These simple dose measurements are unable to provide sufficient information over the wide area where the gamma radiation comes from, unless a huge amount of resources of manpower and hence budget are invested. Given that governments in many countries are confronted with the reactor dismantling issue, detailed and quantitative mapping of the radiation emissivity on the surfaces of reactor facilities, which would be well achievable with the ETCC, would be beneficial. The ETCC has immense potentials for immediate applications to various radiation-related issues in the environment.

Prospects

Some scientists assert that the detection efficiency of gas-based gamma detectors would be too low. However, we have found that some types of gas have sufficient Compton-scattering probability with the relevant effective areas of 110 cm2 and 65 cm2 at 1-MeV gammas with a 50-cm-cubic ETCC using CF4 gas and Ar gas at 3 atm, respectively9. Our prototype 30 cm-cubic ETCC with the effective area of a few cm2 at 300 keV was proved to perform expectedly well in MeV gamma-ray astronomy.

Now, we are constructing two types of more advanced ETCCs: one is a compact ETCC with the similar size and weight to the current model, but having a 20 times larger effective area (0.2 cm2 at 662 keV; type-A) and the other is a large ETCC aimed to be completed in 2018, which has a 1000 times larger effective area (10 cm2 at 662 keV; type-B). The details of Type-B are described elsewhere10.

Type-A has the similar size to the current ETCC, but has an increased TPC volume from 10 cm × 10 cm × 16 cm (rectangular solid) to 20 cm ϕ (in diameter)× 20 cm (cylinder), installed in the similar-sized gas vessel. It has a 5 times larger gas volume and 2.5 times wider detectable electron energy band with the TPC than the current model. In addition, if the mixed gas with Ar and CF4 (50%: 50%) at 2 atm is used, as opposed to the current Ar gas (~90% and some cooling gases) at 1.5 atm, the detection efficiency will be improved by a factor of 29. Then, the resultant detection efficiency (or effective area) will become 20 times larger than that of the current model, while keeping the similarly compact size and weight. The development of Type-A will be completed in 2017.

Type-B will provide the same detection limit for 6 sec exposure. If we perform a survey with Type-B from some aircraft at the altitude of 100 m, we will be able to make a spectroscopic map of a 1 km2 area with a 10 m × 10 m resolution for 1200 sec exposure to achieve the same detection limit, taking account of the absorption of the air. An unmanned airship is a good candidate for the aircraft, it flies slowly for an extended period and hence would enable us to do the precise imaging-spectroscopic survey. Then, the whole contamination area in Fukushima prefecture (roughly 20 km × 50 km) can be mapped with the same resolution as mentioned above in a realistic timescale of ~2 months, assuming 8 hours of work per day. Some of the spectra obtained in our aircraft-based survey might be found out to be generated by the gammas scattered by something, such as trees in woods, within the grid. Our survey will efficiently detect a hint for those areas, which can be then studied in more detail with on-site measurements, such as ones by backpacks11. No successful large-scale survey has been yet performed to monitor the radioactivity in Fukushima. Our upgraded ETCC will be capable of revolutionizing the decontamination work and more. We summarized the specifications of the current ETCC, type-A and type-B in Table 2.

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Methods

Instruments and Measurements

The ETCC was mounted at 1.3 m high from the ground at its centre, tilted 20° downwards beneath the horizontal plane. The average distance to the ground in the FoV is ~4 m, which corresponds to the spatial resolution of ~1 m at the ground for its PSF. As a reference, we also made a mapping measurement of the dose at two heights of 1 m and 1 cm with every 1-m square grid in the FoV (except for the location (A), where the points of the measurements were sparser and irregular) with the commercial dosimeter (HORIBA, Radi PA-1100, http://www.horiba.com). In the dose measurement at the latter height (~1 cm), the top and four sides of the dosimeter were covered by tungsten rubber to shield it from the downward radiation (Fig. 1b).

We have developed a compact ETCC with a 10 cm × 10 cm × 16 cm gas volume, based on the 30-cm-cubic SMILE-II for MeV astronomy9. The ETCC is, like CCs, equipped with a forward detector as a scatterer of nuclear gammas and a backward detector as a calorimeter for measuring the energy and hit position of scattered gammas. The forward detector of the ETCC is a gaseous Time Projection Chamber (TPC) based on micro-pattern gas detectors (MPGD), which tracks recoil electrons. The TPC of the ETCC is a closed gas chamber, and thus can be used continuously for about three weeks without refilling with the gas5. The backward detector is pixel scintillator arrays (PSAs) with heavy crystal (at present we use Gd2SiO5: Ce, GSO). It is noted that, at the time of writing in 2016 after the survey work presented in this paper, we have been developing the Ethernet-based data handling system to replace the existing VME-based system. The latest ETCC available for field measurements is much more compact, which is built in the 40 cm × 40 cm × 50 cm base frame with the weight of 40–50 kg, and operated with a single PC with 24 V portable battery.

The contamination area in Fukushima is the similar environment to the space in the background dominated condition, where the radiation spreads ubiquitously. It is understandable that gamma cameras with the Compton method became the first choice to be employed for the decontamination work in Fukushima, following the precedents in MeV astronomy, even though it is clearly not the ideal instrument especially in the background-dominated environment.

Analytical method for deriving an emissivity from the measured distribution of gammas

Here, we explain how we measure the emissivity (or brightness) based on the proper geometrical optics (PGO) by the ETCC and how we estimate the dose on the ground from the emissivity measured by the ETCC. The following are the reason why no gamma camera but the ETCC can take a quantitative nuclear gamma image with the similar principle to that of optical cameras. According to the well-known formulas in PGO, the relation between emissivity Σ on the ground and detected brightness of the gamma in ETCC (dB) for solid angle Ω is given as Σ · A1 · dΩ1 = dB · A2 · dΩ2. and the relations dΩ1 = A2/D2, dΩ2 = A1/D2 hold, where A1 and A2 are the observed areas on the ground and the detection area in the ETCC (A2 = 100 cm2), respectively, and D is a distance between the ground and the ETCC. Figure 1a gives a schematic demonstration of it. These relations are then reduced to Σ  = dB, which means that the emissivity is equal to the obtained brightness and is independent of the distance D in this optics. In practice, dB is calculated simply from the number of the detected gammas per unit solid angle corrected for the detection efficiency9. We should note that when the distance between a source and the ETCC (L) is comparable with, or longer than, the radiation length in the air (~70 m), dB in a unit solid angle must be corrected for the expected absorption, using the absorption coefficient (α) in the air for gammas with the relation dBcorrect = dB/(1 − exp(−L/α)).

Estimation of the emissivity and the detection limits

We estimate the detection limit using the sensitivity from the calibration data with a point source (137Cs, 3 MBq) in the laboratory17. We detected 662-keV gammas from the point source with a significance of 5σ at a distance of 1.5 m with the exposure time of 13 min. The point source increases the dose at the detector front by 0.015 μSv/h from a background dose. If the same amount of gammas entered the ETCC over the whole FoV, the significance would decrease by  = 0.5σ, assuming that the background gamma increases proportionally from 1 to 100 to the number of pixels. The current ETCC comprises 100 pixels and one pixel is defined as an area of the unit solid angle in the FoV. In the case of a 100 min observation under the dose of 2 μSv/h at the detector front (assuming the case of Location (C), i.e., low dose), the total number of gammas increases by . The expected significance per pixel is then calculated to be 16σ/ = 1.6σ, which is consistent with the observed significances of (1.2–2.5σ) in the low-dose area (see the error bars in Fig. 6b). Similarly, the expected significance for the high-dose area is calculated and is found to be also consistent with the observed values of (3–5σ). Thus, our results of the on-site measurements are well consistent with the expected significances estimated from the calibration in the laboratory.

We also estimate the emissivity within the PSF and the detection limit to check consistency with the calibration data. As shown in Fig. 7 the covered area by the PSF for the distance L between a target and the ETCC is given by L · sinΘ. Since the number of gammas (brightness) within the PSF is conserved along the line of sight, the sensitivity in the PSF is independent of the distance L if absorption in the air is not taken into account. For example, for the distances L of 10 m and 100 m, the sizes of an area corresponding to a detector pixel are estimated to be 1 m and 10 m, respectively, when the same detection limits for both the distances are used. The detection limit for the ~2σ level of the ETCC is 0.5 μSv/h at a unit solid angle for an exposure of 100 min (see the distribution of red points in Fig. 6b). Note that the limit is proportional to , and hence can be easily scaled for different exposures and effective areas.

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Additional Information

How to cite this article: Tomono, D. et al. First On-Site True Gamma-Ray Imaging-Spectroscopy of Contamination near Fukushima Plant. Sci. Rep. 7, 41972; doi: 10.1038/srep41972 (2017).

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

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    Povinec, P. P., Hirose, K. & Aoyama, M. Fukushima Accident: Radioactivity Impact on the Environment. Elsevier, New York (2013).

 

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Takeda, S. et al. A portable Si/CdTe Compton camera and its applications to the visualization of radioactive substances. Nucl. Instr. Meth. Phys. Res. A 787, 207–211 (2015).

 

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    Jiang, J. et al. A prototype of aerial radiation monitoring system using an unmanned helicopter mounting a GAGG scintillator Compton camera. J. Nucl. Sci. Technol. 53, 1067–1075 (2016).

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    Kataoka, J. et al. Handy Compton camera using 3 position-sensitive scintillators coupled with large-area monolithic MPPC arrays. Nucl. Instr. Meth. Phys. Res. A 732, 403–407 (2014).

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    Vetter, K. Multi-sensor radiation detection, imaging, and fusion. Nucl. Instr. Meth. Phys. Res. A 805, 127–134 (2015).

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    Kagaya, M. et al. Development of a low-cost-high-sensitivity Compton camera using CsI (Tl) scintillators (γI). Nucl. Instr. Meth. Phys. Res. A 804, 25–32 (2015).

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    Okada, K. et al. Development of a gamma camera to image radiation fields. Prog. Nucl. Sci. Tech. 4, 14–17 (2014).

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    Tanimori, T. et al. An electron-tracking Compton telescope for a survey of the deep universe by MeV gamma rays. Astrophys. J. 810, 28 (2015).

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    Tanimori, T. et al. Establishment of Imaging Spectroscopy of Nuclear Gamma-Rays based on Geometrical Optics. Sci. Rep. 7, 41511 (2017).

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Cresswell, A. J. et al. Evaluation of forest decontamination using radiometric measurements”. Journal of Environmental Radioactivity. 164, 133–144 (2016).

 

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    Sanada, Y. & Torii T. Aerial radiation monitoring around the Fukushima Dai-ichi nuclear power plant using an unmanned helicopter. Journal of Environmental Radioactivity. 139, 294–299 (2015).

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    Martin, P. G. et al. 3D unmanned aerial vehicle radiation mapping for assessing contaminant distribution and mobility. International Journal of Applied Earth Observation and Geoinformation 52, 12–19 (2016).

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    Takada, A. et al. Observation of Diffuse Cosmic and Atmospheric Gamma Rays at Balloon Altitudes with an Electron-Tracking Compton Camera. Astrophys. J. 733, 13 (2011).

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    Kabuki, S. et al. Electron-Tracking Compton Gamma-Ray Camera for small animal and phantom imaging. Nucl. Instr. Meth. Phys. Res. A 623, 606–607 (2010).

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Mizumoto, T. et al. A performance study of an electron-tracking Compton camera with a compact system for environmental gamma-ray observation. J. Instrum. 10, C01053 (2015).

 

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    Mizumoto, T. et al. New readout and data-acquisition system in an electron-tracking Compton camera for MeV gamma-ray astronomy (SMILE-II). Nucl. Instrum. Meth. Phys. Res. A 800, 40–50 (2015).

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Source: https://www.nature.com/articles/srep41972

 

 

May 7, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Wildfires in Fukushima: reliable data or disinformation?

The forest fire in the Ide area of Namie in Fukushima prefecture, which occurred on April 29, has been going on for almost a week.
See video 消火活動動画
Video and photo sources 写真と動画の出典 : 陸上自衛隊第6師団; JGSD 6th Division
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The major media reported it at the time of the outbreak, but except for some local television news, the fire has not been covered much. Furthermore, the news does not pop out immediately on web sites, and we have to make a considerable effort to find the information. Let’s keep in mind that most of the nuclear accident victims have only cellphones, and not PCs, which makes it very difficult to search for the information if it involves several clicks and the opening of PDF documents.
The danger of the secondary dispersion of the radioactive substances is not mentioned at all in the announcement of Fukushima prefecture (see the picture below).
Equally, no mention is made about the danger on its homepage.
This is the announcement from Fukushima prefecture. The danger of the secondary dispersion of radioactive substances is not given to the residents, though it’s said that there is the possibility of repression of the fire.
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As for the media, about the secondary dispersion of the radioactive substances that accompanies the fire, they say that there is no change in the radioactivity measurement values at present, and that there is nothing to worry about. The local newspaper Fukushima Minyu (in Japanese) calls for attention to the hoax about radiation risk.
The information source of the risk of secondary dispersion of radioactive substances used by the media is the data of airborne radioactivity measurements by monitoring posts and the airborne dust measurement published on the Fukushima prefecture website.
For those who have difficulties to open the PDF files, please look at the pictures below.
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Are these data reliable?
In addition, the public relations of Fukushima prefecture as well as the major media say that there is no influence on inhabitants’ life and health because there is little variation in the airborne radioactivity measurements. Do the measurement values of the individual dosimeters or of the nearby monitoring post help the residents to judge the situation?
Currently, the “Fukuichi (Fukushima Daiichi) Area Environmental Radiation Monitoring Project” group and “Chikurin-sha” are collecting the data of airborne dusts by setting up linen and dust samplers.
We have received comments from Mr Yoichi Ozawa of the “Fukuichi Area Environmental Radiation Monitoring Project”, that we are reporting below.
A. Airborne radioactivity measures in terms of sievert are not appropriate.
“The problem is of that of the increased radio-contamination”
-The sievert is a measure of the health effect of ionizing radiation on the human body, and not a unit of measure of the environmental contamination (becquerel).
-It evaluates how much pollution has come in with the radioactive plume.
-The representative measuring device is a monitoring post (MP) that measures the radiation dose at one meter from the ground. The monitoring posts are installed after the decontamination work of the surrounding environment.
-MP measures only gamma rays, beta and alpha rays are not covered, and thus it is not suitable for environmental contamination evaluation.
-MP gives an average of 10 minutes measurements. Consequently, the result cannot reflect the passage of radio-contaminated plumes of a few seconds.
-Even if the dose is high, if there is less contamination, the fear of internal irradiation is less.
B. Reliability of the data on airborne dust published by Fukushima.
-The time period of the plume collecting in the environment is too short. The air is flowing.
In normal nuclear facilities, dust sampling takes about 20 minutes. It is because all air in the sealed room is absorbed in this time. However, it is not possible to absorb all air in the open environnent. Therefore, it takes a long time to collect the dust and to measure it. In our case, it takes us a week for sampling and from 2 to 4 days for measurement.
-The measurement time is too short. They should continue measuring until cesium 134 is detected.
-The result should be compared to the data before the accident.
-We cannot help thinking that all data are organized in such a way that they are either under the lowest limit (marked as ND – Non Detected) or they conform to the new standards.
We have installed linen cloths at 10 locations and air dust samplers in 2 places. The installation of linen surrounds the fire scene, like in the case of usual measurements of “Fukuichi Area Environmental Radiation Monitoring Project”. They are installed in Namie Town, Futaba Town, Okuma Town, Tamura City, Katsurao village, and Minami Soma City, surrounding the scene of the forest fire (Mount Jyuman in the map).
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It is premature to draw conclusions about the secondary dispersion of radioactive materials.
I think that the peak will come after three to four days after the extinction of the fire. But then, the contamination will continue to move with the wind and rain.
In addition, a summary of the measurement results of the fallen leaves is underway. They are from the border between Namie Town and Katsurao Village, which is 4-5km west of the fire site. The contamination is lower than that of the fallen leaves collected at the Ogaki dam. We are also measuring the burnt ash.
We are working with Mr. Kazuhide Fukada, another member of “Fukuichi Area Environmental Radiation Measuring Project”, living in Miyakoji District, Tamura city. When we burn the fallen leaves measuring 5,710 Bq/kg, we obtain the ash of 19,500 Bq/kg that is, 3.4 times more densly contaminated in terms of weight. We can concentrate the contamination up to about 30 times artificially, but I think this is about the value in the natural environment.
In about two weeks, the data on airborne dust by the citizen groups will come out. We will publish the information as soon as it is known.
However, it is likely that the the environmental contamination fluctuation will become different by this fire, and we need long-term rather than short-term monitoring.
It would be most dangerous to stop monitoring and paying attention after the fire is extinguished. The current media reports seem to be leading us to that direction.
Just after the Tepco Fukushima Daiichi accident, the central government repeated many times that “there is no immediate risk on health”. The major media fled from Fukushima, and they diffused the news from Tokyo, saying that there was nothing to worry about in Fukushima.
We have not forgotten.
Fukuichi Area Environmental Radiation Monitoring Project web site (in Japanese)

May 7, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment