Bericht zu den Nahrungsmittel-Meßgeräten

NCC Japan - Tohoku HELP

September 20, 2012
Sendai/Iwaki Food Radiation Measurement Project
Supporting Documentation for Application

 

Report and Future Prospects

Produced by:
Food Radiation Measurement Project Joint Steering Committee

With the support of a worldwide Christian network via NCC-JEDRO, we have established Food Radiation Measurement Centers in Sendai and Iwaki, and are actively walking alongside disaster victims who are facing fear, anxiety, and distress about radiation. Through this activity, we have become convinced that working to bring peace of heart to radiation disaster victims is essential. We would like to express our heartfelt gratitude for your support, and to give you a report of our activities and future prospects below.

1.Spiritual Care

Unlike other radiation measurement centers run by citizen's groups, we have actively been measuring levels in breast milk and urine, which measure internal exposure to radiation. We have been greatly encouraged by the words of gratitude posted on social networks such as Facebook and Twitter by people who have come to us for measurements. They have been especially grateful for the fact that while doing our best to provide accurate measurements, we have also been trying to walk alongside radiation victims and hear their anxieties and grief.

The Food Radiation Measurement Centers also provide venues for clinical pastoral care (CPC), where professional staff and chaplains have been available to listen to the anxieties and grief of the people who come to us for measurements. They have counseled 81 people over the past few months, and the number is increasing. Many of the visitors have returned several times. This is one of the distinctive characteristics of our measuring stations, and we regard this as an activity befitting radiation measurement centers supported by the worldwide church.

2.Radiation Measurements

a. Measurements and Analysis

Since the opening of the Sendai Food Radiation Measurement Center, 409 samples have been brought in, and measurements lasting at least 3600 seconds have been performed, with the exception of a few cases in which the person bringing the sample has requested otherwise. Measurements that take less time than this can only detect amounts that are higher than European standards, and can therefore only be used for screening. We have endeavored to explain measured values to the people requesting them by minimizing the margin of error. Consequently, when N.D. (Not Detected) is recorded in a report from our measurement stations, it does not mean that the value is below an arbitrary limit (set by someone else), but that it is below the threshold of detection.

We carried out 255 measurements of food alone, excluding cases of soil, water, and human-derived materials, which have different standards from those for food. Levels exceeding the Japanese standard of 100 Bq/kg (April 2012) for radiation in food were found in 12 samples (3.9%). If Ukrainian standards were applied, however, the level would have exceeded the standard in 16 samples (6.2%), and in 26 samples (10.1%) if European standards were applied. When compared with the world's strictest standard, the ECRR standard, levels would have exceeded the standard for adults in 33 samples (12.8%) and for children in 50 samples (19.5%). Because of the high regulatory limit for radiation in Japanese food of 100 Bq/kg, food that would be regarded as not meeting standards in other countries is being distributed without its radiation levels being regarded as a problem, and this food is being fed to children in Japan.

Particularly high levels of radiation were found in shiitake and other mushrooms, bamboo shoots, kiwi fruit, and river fish such as trout. The values detected from these exceeded 500 Bq/kg, levels even higher than the provisional standard imposed immediately after the nuclear accident.

Moreover, these foods containing very high values of radioactive contamination were not only produced in Fukushima Prefecture, but were also brought from as far away as northern Miyagi Prefecture and northern Tochigi Prefecture. As the people who come to this station to request food measurements are probably carefully choosing what they eat with some degree of awareness of radiation risk, the potential risk to those who do not act in this way must be recognized.

Dried foods are believed to contain higher levels of radiation by weight, both because of the loss of mass due to evaporation of water and because shelf-shielding (absorption) by water also decreases. This is true of substances such as tea leaves, which are normally diluted unless eaten dry, and should not be judged on simple radiation measurements alone. This is also indicated in the radiation measurement guidelines issued by the Ministry of Health, which recommend dilution before measuring. We have not adopted this method, however, since it does not take absorption by water into account.

At the Food Radiation Measurement Centers, we have measured 72 urine samples and three breast milk samples to investigate internal radiation. No other private group is performing urine measurements, and measurement of a single sample at a research institute costs up to ¥20,000. Because our centers offer comparatively accurate measurements free of charge, we have therefore dealt with a large number of requests. Urine measurement requires 10 hours for background measurement and 10 hours to measure the actual sample. The equipment is extremely susceptible to lightning, meaning that in seasons when thunderstorms were common measurements were frequently interrupted and staff had to come in to work at weekends. We are overwhelmingly grateful for the strong sense of mission felt by staff members.

To ensure accurate measurements, not only must the dosimeters themselves be shielded, but double and triple shielding with water and lead blocks is also required. The effort involved in ensuring such highly accurate measurements was also reflected in the accuracy of measurement of ordinary food.

No significant radiation was detected from any of the three samples of breast milk. Radiation exceeding 2 Bq/kg was detected in one of the 72 urine samples. This sample contained 8 Bq/kg. Because water absorbs radiation itself (self-shielding), it is more difficult to measure than ordinary food. Since water self-shields radiation, it is more difficult to measure than ordinary food. However, as lake water from Koriyama, which is within the contaminated area, has been measured as containing 40 Bq/kg, the level of 8 Bq/kg detected in urine is obviously abnormal. The urine of two other people who lived together with the person who provided the abnormal sample, however, did not contain any detectable radiation. These two women had been eating different food from the person who provided the sample containing high radiation levels, and had consistently worn face masks. We therefore believe that this exposure was caused by the person having continued to eat contaminated home-grown vegetables from immediately after the nuclear accident, and not having tried to avoid exposure via the respiratory organs by wearing a mask. The half-life of cesium in the adult body is approximately 90 days, and we therefore recommended that she be careful of what she ate and inhaled and be measured again in three months.

b. Measurement Techniques

It took a long time for us to get used to the idiosyncrasies of the dosimeters we used, both before starting measurement activities and even afterwards.

This project uses two dosimeters, the LB2045 and TN300B. Their characteristics are described below.

(1) LB2045

Advantages:

(i) Only requires very small samples.

(ii) Capable of measuring X-rays in the 32 keV low-energy region emitted by Ba137m.

Disadvantages:

(i) Thin shielding (40 mm Pb), meaning it may measure gamma rays from outside.

(ii) Small sample size (420 cc) may cause variation in measured values.

We succeeded in counteracting its disadvantages by adding an extra wall of shielding with water and extending the measurement time to minimize variation in measured values.

We also succeeded in distinguishing other isotopes such as Rn through the detection of radiation (32 keV) from Ba137m, a daughter nuclide of Cs137. This has enabled us to present measurements with confidence even on rainy or snowy days. This achievement is mainly thanks to the efforts of Mr. Sugimoto. We have informed other private measuring stations of our results, and the use of devices capable of measuring 32 keV emissions (such as the FNF401) has now been adopted by many other measuring stations.

(2) TN300B (3-inch NaI scintillation method gamma-ray spectrometer)

Advantages:

(i) Capable of measuring liquids such as urine and water more accurately than the LB2045.

(ii) Manufactured by a Japanese company, this device is very easy to use, with excellent operability that eliminates the possibility of mistaken measurements.

(iii) Has the capacity to hold a 1-liter Marinelli beaker, meaning it can measure specimens more twice as large as the LB2045. A simple calculation shows that this makes it 2.88 times more accurate than the LB2045.

Urine contains only a very small amount of Cs, which is difficult to detect owing to self-shielding. This means, however, that if 1Bq is detected this is extremely significant. Internal exposure is calculated by multiplying the amount of radiation measured in urine by individual constants (80–140), which vary greatly by age and weight. We introduced this device with the aim of enabling better measurements of liquid samples such as urine. However, this is not going as well as we had hoped.

The LB2045 shows the count per second (CPS) of gamma rays as raw data, and Mr. Sugimoto was therefore able to carry out repeated calculations and analyses himself on the basis of these values. The TN300B, however, only displays calculated results, with no way of finding out the intermediate calculations. This means that the limits for detection and quantification are both higher than those of the LB2045. This measuring device is also incapable of measuring 32 kEV emissions from Ba137m, and the spectrum must therefore be verified on the LB2045 if there is a possibility that it may also contain Rn. This equipment is perfectly acceptable as an entry-level device, as it is easy to use and is constructed to prevent mistakes being made during measurements. On the other hand, it contains a "black box," and its specifications are somewhat unsatisfactory for the expert. We must hope the manufacturer will improve this device in future.

For the time being, therefore, rather than using the TN300B for urine and milk measurements, we use it to measure items regarded as likely to contain comparatively higher levels of radioactivity, making use of the fact that it can easily provide comparatively accurate measurements in a short time.

3.Speaking Engagements

Since setting up the Food Radiation Measurement Centers, we have been sending staff to talk about food and how to protect children from radiation. In concrete terms, we have given three talks on nutrition and protecting the body against radiation, and provided nutritional instruction by participating in "Starting Here: Tea-Time Talks for Mothers." We have published Eiyō nyūzu ("Nutrition News") 13 times for users of the Food Radiation Measurement Centers. Eiyō nyūzu can be freely downloaded from the Web site of the Food Radiation Measurement Centers. We intend to continue stay in contact with people who are anxious about radiation (especially parents of small children), and to stand alongside them, as this has become an extremely effective place for doing so.

Rev. Chihiro Saigusa, Director of Tohoku HELP and a member of the Steering Committee of the Food Radiation Measurement Project, also gave six speaking engagements.

4.Issues and Problems to be Solved

Many private radiation measurement stations have been established in the Kanto and Tohoku areas. This can be seen as expression of dissatisfaction on the part of members of the public, who are not convinced by the radiation levels announced by government institutions and want to protect themselves by bringing food samples and measuring radiation levels for themselves. However, there have been cases of doubtful values, which may have resulted from inexperience with processing technology or misreading of values and should probably not have been published, taking on a life of their own.

On the other hand, there are some public measurement stations established by government bodies that take only 15 minutes to measure samples. Such short measurement times may not even be capable of detecting radiation at a detection threshold of 50 Bq/kg. This was also viewed with suspicion at the national Citizens Radiation Measurement Center Network Conference, and has been referred to as hakaru hakaru sagi, "measurement fraud" [a play on words on ore-ore sagi, a type of fraud in which criminals defraud elderly people by pretending to be their relatives over the telephone].

Radiation measurement centers, which should be repositories of public trust, have in fact inflamed public anxiety by publishing measurements on very flimsy grounds. Or else they are being managed by the government under conditions in which it is impossible for them to provide values that can in any sense be described as reliable. In order to prevent this situation from happening, they must both provide technical training for measurement staff, and also provide opportunities for users to request cross-checking by private radiation measurement centers. However, there are only three private radiation measurement centers belonging the national Citizen's Radiation Measurement Center Network that possess germanium-detection (Ge) gamma-ray spectrometers, which provide overwhelmingly the most accurate results. Two of these centers also use liquid nitrogen cooling systems, which entail high maintenance costs, and there is therefore almost nowhere to request cross-checking at a reasonable price. This means that many private radiation measurement centers are losing both the opportunity for cross-checking and public trust, meaning that their valuable efforts are all going to waste.

If possible, we would therefore like to be the first private radiation measurement center in Tohoku to install a Peltier-element system Ge-detection dosimeter in the next financial year.

As the Food Radiation Measurement Project being implemented by Tohoku HELP and CERS Net already uses a Ge-detection dosimeter and has a detection center in Sendai, where atmospheric radiation dose is low, we do not need to look for new premises to install this equipment. We also have excellent members of staff, who have experience of carrying out experiments using Ge-detection dosimeters at national research institutions. The TG150B Techno AP Ge-detection dosimeter we are currently hoping to install uses Peltier elements (electric) to cool the Ge counter, meaning it has lower

running costs compared with devices that use a liquid nitrogen system. This device is currently used at the Ichinose Laboratory in Nagano Prefecture, and is proving to be of great use in the Kanto area. If we could install this model, we would not only be able to carry out highly accurate measurements of breast milk and urine, but also to provide opportunities for cross-checking results from other private radiation measurement centers across a wide area, enabling us to support more accurate measuring activities. This would be very good news for the people caught up in the maelstrom of radiation damage and trying to protect the lives of their loved ones. Measurement centers with the ability to make the best use of this device will benefit massive numbers of people.

If we are only talking about providing temporary peace of mind for those people who come to our measurement centers with fear and grief in their hearts, our current devices would be sufficient. However, if we are to offer true peace of mind to the many people connected with other private radiation measurement centers, we judge that we require the same type of system as that used in public institutions.


 

   

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