Information about the effects of the reactor disaster in Fukushima on the worldwide networked

Transcription

1 We make radiation measureable! Information about the effects of the reactor disaster in Fukushima on the worldwide networked economy Detect radiation in a reliable way

2 The reactor disaster of Fukushima and its effect on global trade The reactor disaster of Fukushima began on March 12th, Together with the reactor disaster of Chernobyl, it is the biggest nuclear accident in the world. The disaster in the reactor blocks of nuclear power plant Fukushima, caused by the destroying earthquake and the following tsunami, will have worldwide radioactive consequences. Radiation protection and radiation measuring equipment When measuring radiation, several tasks and measuring units have to be observed: contamination dose and dose rate activity Contamination measurement A contamination is in general a pollution. Due to the reactor disaster, the release of radioactive material through the air and water (both sea and drinking water) have lead to large-area contamination, still getting larger and larger. Directly, the Japanese population is in danger by the radiation coming out of the destroyed reactor building, by contamination trough the air as a result of the explosion and by large quantities of contaminated water in the sea. The concerned radioactive material (Cesium-137, Iodine-131, Strontium-90, Plutonium-238) are spread all over the world via different exposition paths in the next weeks and months. The concentration of the radioactive material will decrease, but cannot be avoided completely. Apart from natural diversion by air and sea, radioactive contamination is also forwarded by our worldwide economy. Though the quantity of food coming from Japan to Europe is relatively low, Japan is one of the most important manufacturers of electronic components and instruments. From the smallest condenser to an LCD screen, the Japanese industry supplies their products all over the world. In Europe, these electronic components are used in televisions, cars, aircrafts, measuring instruments etc. For this reason it is extremely important to check all products manufactured and transported after the reactor disaster for contamination. We would like to give you some clearly understandable hints regarding the possibilities of radiation measuring equipment. Like the oil during the disaster in the Gulf of Mexico, which was spread over the whole region, the radioactive contamination is spread in a similar way. Depending on the nuclides, we distinguish between alpha (α) contamination or beta (β) and gamma (γ) contamination. To measure these contaminations, contamination monitors with so-called large area detectors are used, like for example modern plastic scintillation detectors. One of the most modern instruments of this kind is the CoMo 170, a digital, portable contamination monitor with a detector surface of 170 cm² (picture 1). This instrument has a plastic scintillation detector which works completely without gas, contrary to older monitors with gas-operated detectors. picture 1: mobile contamination monitor

3 Contamination is measured in Becquerel (Bq) or Bq/cm². Becquerel means: decay per second. A measuring value in Bq or Bq/cm² is always based on a radioactive material (nuclide), for example iodine (I-131) or cesium (Cs-137). The detector in a contamination monitor has different efficiencies for each nuclide. This efficiency depends on several physical factors, for example the radiation type (α, β, γ) and the energy of the nuclide. In table 1, some data are summarized. Radionuclide efficiency Average values from measurements with 100 cm³ test sources Sr-90 / Y-90 (based on Sr-90) approx. 42 % I-131 approx. 21 % Cs-137 approx. 35 % Pu-239 α approx. 18 % U-238 α approx. 22 % table 1: efficiencies CoMo 170 Summary With a contamination monitor you can measure α- and β-/γ-contamination. The contamination is measured in counts per second (cps) or nuclide-related in Becquerel (Bq) or Bq/cm². A contamination monitor has a planar detector which is protected by a very thin foil (mylar foil). This foil may not be damaged during measurement, i.e. whilst scanning a surface. If you want to measure for example complex machines or machine parts with many edges and corners, it can be better not to carry out the measurement directly, but to measure indirectly by means of a smear test (also called wipe test). In case of a smear test, the surface of the object (for example a machine) is wiped with a small swab, often made of cotton, and this swab is used as a smear test sample to be measured in a smear test counter (picture 2 and 3). Our contamination monitors, for example the CoMo 170, are used by institutions like the German wetter services, customs, harbour authorities, federal institutes for environment, forwarders and logistics companies. The basic measuring unit of radiation is Counts Per Second (cps). This means: The detector and its electronics measure the counts generated in the detector by radiation. If this count rate is multiplied by the nuclide-related efficiency, you get the corresponding measuring value in Becquerel (Bq). In case of the CoMo 170, the detector has a surface of 170 cm². This means that the measuring value in Bq can be divided by 170 cm² in order to get a measuring value in Bq/cm². According to the advisory results of the crisis management group from the German Commission on Radiological Protection (SSK), the following contamination limit values apply to cargo, goods and persons: 4 Bq/cm² surface contamination with β- and γ-radiation, measured over 300 cm² picture 2: CoMo 170 in a smear test station 0.4 Bq/cm² surface contamination with α-radiation A nuclide-specific measurement of radionuclides is not required. With the contamination monitor CoMo 170 you can measure α- and β-/γ-contamination at the same time. In order to measure α-contamination, the detector foil must be very, very thin (only some micrometers!), as α-radiation is already shielded by a sheet of paper. This could make you think that α-radiation is not dangerous. That however is not true at all. α-radiation as a very high energy. If this radiation is coming into the body a so-called incorporation the high energy of α-radiation needs just a very short way to reach the cells and destroys these (which can lead to cancer). Furthermore, some α-nuclides also have a high toxic (poison) effect. picture 3: WIMP 60 M mobile smear test counter

4 Professional instruments like the CoMo 170 also have their price and are often too complex and too expensive for private use. There are however also more simple, cheaper contamination detection instruments. These systems work with an end window detector or a so-called pancake detector. Theirdetectors have for example a surface of cm² and a thin mica window. This makes it possible to measure α- and β-/γ-contamination with low comfort. It means for example that the distinction between α- and β-radiation has to be made by means of two measurements after each other. During the first measurement, α- and β-radiation is measured. The second measurement is made with a sheet of paper between detector and measuring object in order to shield the α-radiation and only measure the β-radiation. The difference between the two measuring results is the α-part of the radiation. An example of such a simple contamination meter is the MiniTRACE β (picture 4). Dose and dose rate The dose (radiation dose) is an indication for the radiation absorbed by the body. Dose is measured in Sievert (Sv). The limit values for dose permitted by law are different for several person groups, for example common people and radiation workers. Based on the whole body, the following dose limit values are valid inside the EU: Common people Radiation workers category A Radiation workers category B 1 msv per year 6 msv per year 20 msv per year table 2: dose limit values The dose is measured with dosimeters (integrally over a certain time period) or with dose rate meters (measuring the actual dose rate level at a certain place (for example 1 µsv/h)). The environmental, natural radiation (coming from the earth (terrestrial radiation) and from the universe (cosmic radiation)) in Germany has a dose rate value of nsv/h = µsv/h. This dose rate level means a dose of approx µsv/year = 1 msv/a. According to the current knowledges of research and economy, the total dose during a working life, for example 20 msv/a x years = msv = Sv, does not lead to verifiable damages. picture 4a: MiniTRACE β front side Dosimeter With an electronic personal dosimeter, the γ-radiation working on the body is measured and indicated on an LCD, for example in µsv. The DoseGUARD S10 is a battery-operated dosimeter (picture 5). Additionally it has the possibility to set alarm thresholds for dose and dose rate. In this way the dosimeter warns in case of a high dose rate or when the maximum allowed dose is reached. A dosimeter is carried close to the body, for example in a breast pocket. picture 4b: MiniTRACE β backside picture 5: personal dosimeter DoseGUARD S10

5 Dose rate meter With a dose rate meter, the currently present dose rate level on the place where you stay is measured. The measuring value is expressed in µsv/h. For example: In case of a dose rate level of 2 µsv/h, you will get a dose of 2 µsv if you stay there for 1 hour. Dose rate meters with a Geiger-Müller counter tube can measure current dose rate levels starting from approx µsv/h in a reliable way. The simple, cheap dose rate meter GammaTwin offers a double function. It shows on its display: the current dose rate, measuring range 0.5 µsv/h - 70 msv/h, and in addition at the same time the accumulated dose, that means you can sum the dose over a day, a week or a month. Dose rate meters with a scintillation detector (for example sodium-iodine (NaI) detector) are definitely more sensitive, but also more expensive. With a scintillation detector you can measure from 40 nsv/h, so you can start from environmental background and detect changes / increases of background in a fast and reliable way. Therefore, high-sensitive dose rate meters with NaI-detectors are very good to detect γ-contaminations. Compared to a contamination monitor, measuring instruments with an NaI-scintillator are mechanically more robust. The German Commission on Radiological Protection (SSK) recommends to use the double background value as a limit value for a γ-contamination. In this point of view the SSK follows the practice of for example customs and practical radiation protection. The double background value is depending on the location, normally approx nsv/h ( µsv/h). As an example for dose rate meters we would like to present the GammaTwin and the SCINTO (picture 6 and 7). picture 7: GammaTwin Pallet monitor PaIMo To control incoming goods for the presence of radioactive contamination, articles packed in cardboard boxes or on EUR-pallets have to be checked in fast and reliable way (pict. 8). With the pallet monitor PalMo, only γ-contamination can be detected. α- and ß-contamination of the goods cannot be checked from the outside, as these kind of contaminations are shielded by the packing material. The pallet truck with measuring object(s) has to be moved through the PalMo slowly. picture 6: SCINTO picture 8: pallet monitor

6 RAMBO IIn global trade, the container is nowadays the standard transport and packing unit for all kinds of goods transport. Outside radioactivity monitoring of closed containers can only be done for γ-radiation with large-area plastic scintillation detectors. α- and β radiation cannot go through the metal sides of the container. The RAMBO system is installed as a gate and checks the container and its content for the presence of γ-radiation and/or γ-contamination whilst driving through the detector pillars (picture 9). With this high-sensitive measuring method, increases in radiation level by approx. 100 nsv/h can be detected in a reliable way. If a radioactive cargo is detected by the RAMBO, a mobile instrument (CoMo 170 and/or SCINTO) can be used to check the container s content in detail. Since many years, the RAMBO system has proven itself as a high-sensitive radiation monitor in daily practice in the scrap and recycling field, border-crossing goods transport etc. For smaller transport units, but also for person control, the RAMON radiation monitor pillar (picture 10) or the very flexible FAMO-system (picture 11) can be used. picture 11: FAMO The high-sensitive measuring SCINTO system (pict. 6) uses an NaI-crystal as detector. To check for example a container of packed objects / machine parts for the presence of radioactivity, the SCINTO is the right measuring instrument. For γ-radiation, the SCINTO has an excellent detection sensitivity. Even a slight increase of background is detected in a fast and reliable way. picture 9: RAMBO Food monitoring Due to the emission of radioactive material, food can be polluted by this. The unit for activity is Becquerel (Bq) or, based on volume / weight Bq/l or Bq/kg. The EU has determined limits for activity in food. The limits for foodstuff (imports from Japan) according to the new EU ordinance are as follows: Foodstuff Iodine Nuclide swith isotopes T1/2 > 10 days e.g. Cs-137 Baby food 150 Bq/kg 400 Bq/kg Milk products 500 Bq/kg 1000 Bq/kg Other food 2000 Bq/kg 1250 Bq/kg Liquid food 500 Bq/kg 1000 Bq/kg picture 10: RAMON The activity in foodstuff is measured and monitored by several accredited laboratories. For self-monitoring, activity counters like for example the ANNA-system can be used (pict. 12).

7 Summary We hope this overview has helped you to get a better understanding of radiation protection and radiation measuring equipment. We are happy to help you in case you have any questions. We make radiation measureable! For more detailed and up-to-date information please look at picture 12: ANNA With the ANNA activity counter, solid and liquid food can be checked. The system is calibrated for Cs-137 and I-131. The measuring values are displayed in Bq, Bq/l or Bq/kg. An integrated multi-channel-analyzer shows the radiation spectrum. At the moment we are developing a small, cheap food counter type EL25 (pict. 13). This counter is also very suitable for private use or for restaurants. The price is approx. 40% of the ANNA system price. picture 13: food counter EL25

8 Subject to technical changes 05/11 Headquarters: D Dülmen Ostdamm