From Professor Koide

Original text from Blog of Koichi Oyama in Minamisoma City 11.07.2012 http://mak55.exblog.jp/16318274/

2012 June 29 

A note on measurement of "black substances" 

Hiroaki Koide, Kyoto University Nuclear Reactor Laboratory 

1. Introduction 

More than a year has gone by since the accident in Fukushima. 

About hundred thousand people evacuated from the highly contaminated area of northeast of the plant, which measures the radiation level of  600.000 Bq/m2. 

However, according to the laws of Japan, the extensive areas over Tohoku and Kanto,  which measures the radiation level of  40.000 Bq/m2, should be designated as radiation controlled area and the people should evacuate. 

The government decided the extensive land couldn't be given up, therefore abandoned the people there. These people have no option but evacuating home if they want to protect themselves from radiation, however, the government intends not to pay any compensation. 

Some people evacuated by their own. In other cases, fathers stay home while evacuating children and mothers. 

However, for farmers, daily farmers or breeders, the land is the life itself, so it's hard for them to leave the place. 

At the moment, about a million people live in radiation controlled area, have babies and bring them up. 

The government try to make us believe conducting a decontamination operation will reduce the amount of radiation exposure, but human being are not able to conjure away radioactivity. 

"Decontamination" in Japanese consists of two characters, which are "remove" and "contamination", however, it's impossible to remove radioactivity. 

Only what we can do is move the radioactive materials to other place. 

Therefore, I prefer this word, "Moving contamination". 

Apart from the decontamination work conducted by human, nature also moves the contamination. 

Fallout on mountains run down toward lower, and the rivers carry them to the oceans. 

Also, Cesium, which is the biggest source of exposure, get attached to the dirt and thus enriched. 

I heard about the "black substances" long time ago, found in the areas where people are abandoned and children have normal life. 

Prof. Tomoya Yamauchi of Kobe University quickly began to examine the substances, and found they were dead algae (blue-green algae) that measure the high radiation level of Cesium. 

I also got an opportunity to measure the algae. I would like to report the result. 

2. Samples and Measurement 

I received the samples from two different routes. One is from downtown in Tokyo and Tama district, while the other from Minamisoma. 

Minamisoma is highly contaminated and the Cesium radiation level there is over 100.000 Bq/m2, while the part of Tokyo near Chiba, such as Katsushika or Edogawa, measures the radiation level over 40.000 Bq/m2. 

The following figure is the sample list. 

Fg.1　"black algae" sample list 

Sample name/collected place/amount/container

Tokyo 1 Higashi Murayama City, School 0 (1/2) 100cc, polyester container 

Tokyo 2 Higashi Murayama City, School 0 (2/2) 100cc, polyester container 

Tokyo 3 Katsushika,  Minamoto Park  3100cc, polyester container 

Tokyo 4 Katsushika,  Minamoto Park  4100cc, polyester container 

Tokyo 5 Katsushika,  Minamoto Park  5100cc, polyester container 

Tokyo 6 Katsushika,  Minamoto Park  6100cc, polyester container 

Minamisoma Fukushima 1 Kawafusaoku01, polyester bag 

Minamisoma Fukushima 2 In front of a shop "Kanatani" 07, polyester bag 

Minamisoma Fukushima 3 In front of a shop "Kanatani" 08, polyester bag 

Minamisoma Fukushima 4 in a dish

I made a measurement of the samples using gamma spectrometry with Ge semiconducting detector. As described in the next chapter, the samples contained high concentration of Cesium, so opening the containers or replacing the samples to measurement vessel was restricted as much as possible. However, regarding some samples collected in Minamisoma, the amount of radioactivity was too much and dead-time of the measurement system sometimes exceeded 90%, so that I had to take a portion of the samples to make a measurement. I made some measurements in a container just as it was received. In such cases, a vessel that efficiency calibration has been done wasn't used, therefore, please note that the results might have about 10% of margin of error. Considering these are environmental samples, I think the results are certainly acceptable. 

Fig.2.　"black algae" condition of measurement etc. 

Sample name/measuring state/measuringt date/weight/measuring time

Tokyo 1/100cc in a polyester container/2012May3/05476.2

Tokyo 2/100cc in a polyester container/2012May3/057100.7

Tokyo 3/100cc in a polyester container/2012May3/0618.1

Tokyo 4/100cc in a polyester container/2012May3/05111.3

Tokyo 5/100cc in a polyester container/2012May3/0729.55

Tokyo 6/100cc in a polyester container/2012May3/0659.93

Minamisoma 1 /a portion in a big dish/2012Jun7/0.686.28

Minamisoma 2 /a portion in a big dish/2012Jun7/1.09.8

Minamisoma 3 /a portion in a big dish/2012Jun7/1.016.7

Minamisoma 4/in a dish/2012Jun7/1209.95

Results of measurement 

Fig.1 shows a typical spectrum. 

Fig.1 is the result of "Tokyo 1"sample replaced to a vessel that efficiency calibration has been done, and measuring time was 982 minutes (from the evening till the following morning). Since it was a long-period measurement, natural K-40 and Bi-214 as a background of measuring system also appear on the spectrum. However, the high concentration of Cesium 137 and 134 are contained, which appears as a clear peak. 

The samples of Minamisoma contained much higher concentration of Cesium. When I measured gamma dosage rate on the surface, the radiation level exceeded 100 microSV/h. I applied the samples to Ge detector, but the dead-time of the detector exceeded 90 % so that I could no longer make a normal measurement. I took a portion of less than 1 gram of the samples, and spread it as a thin layer in a large dish (50cmφ) which efficiency calibration had been done to make a measurement. The measured spectrum (of the sample of Minamisoma 1) is shown in Fig. 2. Though I measured only 0.68 gram of the sample for 6.3 minutes, Gamma ray of Cs-137 and Cs-134 achieve a clear peak and the natural nuclides as the back ground of measuring system are not seen at all. 

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Fig.3 shows the concentrations of Cs-134 and Cs-137 contained in each sample, 

Fig.3　Cesium concentrations in "black algae" (Bq/kg) 

Cs-134+Cs-137

Tokyo 1　　　　14,000±8,500±59　　　　22,000±140

Tokyo 2          　13,000±8,400±51　　　　22,000±120

Tokyo 3 170,000±870110,000±720　280,000±1,600

Tokyo 4 180,000±860110,000±640　290,000±940

Tokyo 5 150,000±68089,000±500　　240,000±1,200

Tokyo 6 120,000±59074,000±470　　190,000±1,100

Minamisoma 1

3,800,000±21,0001,900,000±14,000　5,700,000±35,000

Minamisoma 2 1,500,000±8,800760,000±6,100　2,300,000±15,000

Minamisoma 3 1,900,000±7,600990,000±5,400　2,900,000±13.000

Minamisoma 4　　　　6,700±79　　　　　　4,300±63　　　11,000±140

The black algae collected in Minamisoma contain 2.000.000-6.000.000 Bq/kg of Cesium. The samples collected in Minamoto Park in Katsushika, a downtown of Tokyo, contains 200.000-300.000 Bq/kg of Cesium, and the sample collected in a school in Higashi Murayama contains more than 20.000 Bq/kg of Cesium. 

According to the laws of Japan, Cs-137 and Cs-134 over 10.000 Bq/Kg is radioactivity. Such materials are supposed to be strictly controlled and not allowed outside of radiation controlled area. However, today, they exist where the people are living. 

4. Things to be done

Due to the fallout from Fukushima, in the extensive area covering Tohoku and Kanto, the levels of cesium radiation exceed the standard of radiation controlled area (40.000 Bq/m2). The government are aware they abandoned the people in the contaminated areas. At the moment, more than one million people including children are forced to live in the areas. As I reported, some substances (or living beings) that have high concentration of Cesium are scattered as "micro hot spots" everywhere in these area. Those micro hot spots were found even in a place like Higashi Murayama, that doesn't get as much damage as the standard radiation controlled area. These are supposed to be controlled as radioactive materials. 

If the Japanese government intends to follow its own law, it is required to remove and control the algae, especially from the place such as a park where children come to play. 

Lastly, I express my gratitude to the many people who struggled to collect the samples. 

Courtesy : Koichi Oyama