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To use the information got from the dosimeter right, there is general information about radiation given below.
Radioactivity and its attendant radiation exist on Earth long before the life birth on it. That’s why life development on Earth is always occurs in the presence of environment background radiation. Every person is exposed to irradiation from natural radiation sources. Radioactive materials may be outside the body and is exposed from outside; in this case we speak of external irradiation. Or they may be in the air that man breathe, in the food or water and get inside the body. Such way of irradiation is called internal.
The picture shows the distribution of the average annual dose from natural radiation sources and their average contribution to the external and internal exposure of the human body.
The radiation background produced by cosmic rays, gives a little less than half of the external exposure. Cosmic rays are coming to us from the depths of the Universe, as well as from the Sun during solar flares. Exposure due to cosmic radiation depends on latitude because of the radiation belts of the Earth at the equator – it is less (0,35 µSv/year), at the poles – it is more (0,5 µSv/year), and mostly it depends on the altitude because of a decrease in the amount of air, which serves as a protective screen. Thus, if on the sea level power dose that influences on people is 0,3 µSv/h or 3 McR/h, then at 4000 m is 0,2 µSv/h (20 McR/h), and at an altitude of 12000 meters is already 5 µSv/h (500 McR/h). However, it should be noted that finding the man at the height is relatively short and contribution to the annual dose even from a transatlantic flight, is small.
Earth's radiation levels vary for different places of the globe and depend on the concentration of radionuclides in some parts of the Earth's crust. In residence places of the general population, they are almost identical. The main isotopes found in rocks of the earth and food – is potassium-40 and two components of the “radioactive families”, originating respectively from the uranium-238 and thorium-232, of which the most “practical” significance (3/4 of internal exposure ) is radioactive gas radon (it is 7,5 times heavier than air and has no taste or smell). Radon is released from the crust everywhere, but most of the radiation dose from radon people receives while in the closed not-ventilated area (radon concentration in non-ventilated areas at about 8 times higher than in outdoor air). The use of some building materials and some ores processing waste in the construction of buildings or site areas backfill can significantly increase the release of radioactive radon gas and increase the levels of external radiation background.
Over the past few decades, man has learned to use the atom energy for different purposes, which led to increase in radiation dose both for the whole population, and individuals. Herewith, on the average, the share of man-made radiation sources (formed as a result of human activity) in the irradiation of the world's population is about 20% of the total dose received. The main contribution to man-made radiation of people is made by medical treatments and treatment modes (x-ray examination and treatment of oncological patients, etc.).
“Average” doses, that we previously discussed, are very small, but actually received doses for certain population groups may differ significantly from the average, and for individuals they can simply represent significant value for health.
Nuclear weapons testing, work of nuclear power engineering plants, radiochemical plants can cause air pollution and pollution of the areas with artificial radionuclides (iodine-131, cesium-137, strontium-90, etc.). The Chernobyl nuclear power plant accident led to high population exposure of some BSSR, USSR and RSFSR areas. Local pollution focuses in some places of SSSR European part and Transcaucasia. Therefore, the population self-assessment of the radiological situation on contaminated as a result of an accident territories or near the radiation-hazardous facilities is justified rational by the National Committee on Radiation Protection (NCRP) of the Russian Health Department
Your dosimeter is intended for measure of the dose rate per time unit. Remember that the effects of irradiation are not determined by a dose rate, but total dose received, i.e. dose rate multiplied by the time during which a person is irradiated.
For example, if the dose rate of external radiation is 0.11 µSv/h (11 McR/h), the exposure during a year (880 hours) creates a 1000 µSv/h or 1Sv (100 mR) dose.
The dose rate of natural background is usually 0,1-0,2 µSv/h (10-12 McR/h) and, as it was said before, according to the local conditions can change in two or even more times.
There are areas where the dose of radiation from natural radionuclides reaches 0,6 µSv/h or more (for example, in the areas of the rocks outlet to the earth's surface, or some granites), but it’s usually insignificant to area.
Allowable levels of dose rate values are derived from the dose, which is controlled by sanitary regulations. This way, allowable irradiation dose for professional workers is set to 50 µSv/h. For population that lives near nuclear power stations and other plants National Committee on Radiation Protection (NCRP) set the limit of annual dose – that is 5 Sv/h. This limit corresponds to a constant dose during the year, the dose rate in open areas is 0,6 µSv/h (60 McR/h). In consideration of the fact that buildings weaken radiation to two or more times, the dose rate in open areas can be 1,2 µSv/h.
If the dose rate exceeds 1.2 µSv/h, it is advisable to move off this place or reduce the time spent.
Evaluation of radiation environment using a dosimeter will allow you to always have an idea about the real impact of radiation dose, and if necessary, to choose the place (to protect) with less background radiation.
If you purchased a dosimeters, and you know (according to local radio, press, etc.) that the level of background radiation in the place of residence is "normal", it is recommended to conduct a series of "baseline" measurements.
To do this, select several points of measurement: indoors, outdoors, in the garden. In each of the selected points make 3-5 measurements. Make sure that the readings on the liquid-crystal display of the dosimeter at the level of background radiation for the area. The results for each selected point are to be averaged. These results in µSv/h (McR/h) are helpful to be write down.
Hereafter, periodically control the level of radiation background at these points. In changes of dosimeter measurement results, you may find the change of radiation situation at the expense of the additional appearance of man-made sources of radiation.
Increase in the average measurement results twice should be considered authentic. Using doses from 0,6 to 1,2 µSv/h, you should inform the local radiology lab (group), Sanitary & Epidemiological Service, and for large values to assume additional protective measures. Such measures might include: finding a room with the help of a dosimeter with a lower level of background radiation, tightly close windows and doors of rooms where you are. Listen carefully to local radio. In the case of message given by radio of the appropriate iodine prophylaxis take 2-3 drops of iodine tincture, dissolving them in a glass of milk, jelly, etc. Later strictly follow the guidelines for the behavior of the population that are given by local broadcasting centers.
If you are on the territory of which it is known that it is contaminated with radionuclides due to accidents :
2.1. Follow all instructions on radiation protection of the population given by the local radio center!
2.2. With a dosimeter find a place where radiation levels are less and try, if possible, to spend more time at such places. When you come to the room from the street or other polluted areas make pollution control of your shoes, clothes, hands, hair, holding the device to the inspected area, focusing on the results of measurements or changes in the intensity of sound signals (listening, not counting them). If you find radioactive pollution, do a simple decontamination by shoes washing, clothes cleaning (both best done outdoors), hand and hair washing. After making a decontamination, do pollution assessment with a dosimeter and check the effectiveness of measures taken.
2.3. If decontamination hasn’t given proper effect, take off contaminated items, put them in a plastic bag and turn to the radiology lab (group), Sanitary & Epidemiological Service for advice on their further use.
Staying on the contaminated territory inevitably leads to a gradual contamination of the premises. DO NOT STAY INDOORS IN THE SHOES WHICH YOU ARE WALKING OUTDOORS! CHANGE SHOES WHEN ENTERING THE HOUSE OBLIGATORY! PROTECT DOSIMETER FROM RADIOACTIVE CONTAMINATION!
Check premises regularly with a dosimeter. If you notice a significant increase in frequency on hearing sounds, do a "wet" cleaning, wash linens. If washing the linens does not lead to a positive effect (which is to be judged on dosimeter), replace linens, consult the nearest dosimetric station or Sanitary & Epidemiological Service about the possibility of its use.
It should be remembered that the radiation control of things, etc. after decontamination should be carried out in places with minimal background - it increases the credibility and effectiveness of controls.
2.4. You should not eat milk and meat produced in the area, which the pollution has reached or exceeds the level of gamma rays exposure rate 1,2 µSv/h (120 McR/h). The possibility of using animal products produced in the area, which level of dose is less than 1.2 µSv/h, is solved by Sanitary & Epidemiological Service.
It should be remembered that after the accident radioactive contamination of the territories is initially superficial and simple sanitization of fruits and vegetables (washing and cleaning) is almost completely decontaminate these products. Later, when radioactive isotopes as a result of natural biological processes get inside of fruits and vegetables, washing of these products does not give positive effect.
2.5. With the help of the dosimeter you can control not only the radiation situation in the environment, but also assess radioactive contamination of food by their external gamma radiation . The minimum level of contamination that requires attention, as recommended by the NCRP is 4 kilobecquerel per kilogram (litre) – 4 kBq/kg (l) or 1 . 10-7 Ci/kg (l).
Currently, the contamination is mainly due to the cesium-137 isotope, which concentrates in milk and meat products. Contamination of other food has no significant effect (exposure) on human body, although, for example, contamination of mushrooms can cause a significant increase in dosimeter readings.
To control the contamination level of milk or meat products dosimeter must be placed close with the back cover to the container with 1 liter of milk or 1 kg of meat (can be through plastic lamina or paper). If the contamination of controlled product reaches 4 kBq/kg, the dosimeter readings should increase to 0,15 µSv/h (15 McR/h) above the background. If such contaminated food is found, it is recommended to abandon their consumption or limit consumption to twice its normal ration. If the radiation of food increases the dose rate from 0,3 µSv/h above the background level, the consumption of such products must not be more than a quarter of the usual ration, for 1 µSv/h – less than one-tenth, etc.