Radiation: the most radioactive places in Moscow and not only


    Radiation is everywhere. There is she in Moscow. And I walked my new home-made scintillation radiometer (there will probably be a detailed publication about it soon) to find out which places in Moscow are the most radioactive, what is the source of this radiation and how bad it all is.

    Devices and techniques

    I made the main measurements with a self-made scintillation radiometer under the code name Envi RAD 100. The basis of the radiometer is a detector based on a CsI (Tl) crystal with a size of 8x8x50 mm and a SiPM photodiode. The owners of Atom Fast probably saw something familiar in this and they will be right - a detector from him. The radiometer was calibrated using an exemplary Cs-137 source of known (about 100 kBq) activity, a lead “house” to reduce and stabilize the background and ruler, and was confirmed by comparison with a trusted dosimeter.

    The measurements were carried out in the direct pulse counting mode. In this mode, the scintillation radiometer has a significant stroke with rigidity. However, there is most likely no significant contamination by technogenic radionuclides in Moscow (with the exception of certain local places - Kolomenskoye, Shchukino), and the average energy of gamma rays of the natural background is close to the energy of cesium gamma rays, and the error associated with this is due to -for this is small and does not exceed 15%.

    When measuring the dose rate on the ground, the radiometer was located a meter from the surface of the earth. In all other cases, I will specify the distance.

    Another point is the contribution of cosmic rays. The dose rate from the latter at sea level is about 3.5 μR / h, but my device practically does not see them (the approximate expected count rate from cosmic rays with a horizontal crystal is 4 imp / min, while the count rate from the natural background is approximately 600 cpm). Fundamentally, this does not change anything, and the level of cosmic radiation is the same everywhere (except for deep underground stations) and almost does not change in time. If you want, you can add 3.5 μR / h to all my numbers.

    Radiation in nature

    To begin with, I decided to measure the natural background, minimally affected by the city. To do this, I walked around the city of Pushkino - near the Ucha river and the Uchinsky reservoir. To begin with, I chose an open area, remote from possible man-made sources of radiation (such as a railway embankment and a bridge, as well as asphalt of the road containing granite gravel), as well as from radiation-shielding objects (forest, river). A noticeable variation in the background dose rate from point to point was established, as well as its fluctuations (apparently due to the release of radon from the soil), so 25 measurements were taken at different points with subsequent averaging. The average value was 6.4 μR / h with variations from point to point in the range from 4.5 to 10 μR / h. Also found a "hot" spot with a dose rate of 15-18 μR / h without any visual signs, possibly

    I thought I got a representative background value until I went into the forest. And he discovered a curious phenomenon: in the forest , the dose rate is steadily and statistically significantly higher than nearby not in the forest . Moreover, it is the fact of the presence of the forest that matters, and not the geochemical features of the soil - the radiation level at the site of the cut down forest is also lower. With what it can be connected? I don’t know. I can only assume that lead-210 from the radon "daughters" settles on the leaves and shines from everywhere, or the forest interferes with the blowing of radon and its DPR accumulate on the soil, or there is a mechanism like that which leads to the appearance of hard x-ray radiation during rain - due to the interaction of secondary cosmic radiation with drops (and in this case, with branches and leaves).

    The second interesting phenomenon is a clear correlation between the level of radiation and soil moisture. As the soil under the feet turns from dry, first to wet, and then to a viscous nyasha, the dose rate above it sharply, up to two times (3-5 μR / h above the nyasha), decreases. Here the nature of the phenomenon is understandable - with an increase in water content, the amount of solid substance with which activity is associated decreases.

    Similarly, the level drops when approaching water. If you go into the water waist-deep with the device, a few meters away from the shore, he simply “forgets to count” - the display shows 1.5-2.5 μR / h.

    In general, the level of radiation, even in the absence of its obvious sources, turned out to be quite variable. Therefore, for a more accurate assessment of the baseline, I used the total accumulated dose counter on the radiometer screen and got the average value for all outdoor activities on Sunday, dividing the difference in the readings before and after walking outside the city by its duration. The result was 8.21 μR / h.

    ... and in the city

    The radiation levels in Moscow are mostly slightly higher than the values ​​prevailing in a clean field. In some places, the excess is quite significant.

    Almost all identified areas with an increased background are confined to large masses of granite cladding. The highest levels were observed on the stairs. The characteristic level in these places is 25-35, sometimes up to 40 μR / h. This level was found on the steps of the native institute (GEOKHI RAS), the steps at the entrance to the Vorobyovy Gory metro and the stairs leading to ul. Kosygin, on the stairs leading from the Yaroslavl lobby of Art. Komsomolskaya on the Komsomolskaya-Radial platform, underpass stairs under the Pushkino station. Higher levels are found in the underpass from the area of ​​the Kursk station on the street. Zemlyanoy Val opposite the exits from the metro Kurskaya-Koltsevaya and Kurskaya-NPS. In this transition, the dose rate exceeds 50 μR / h and the highest levels again on the stairs.

    The reason for such a high activity of the stairs, apparently, in the thickness of the granite steps compared with the facing tiles.

    The screenshot shows a typical picture, if you go along Komsomolskaya from the underground entrance from the Yaroslavl train station via turnstiles and onto the red branch.

    Moderately elevated (up to 15-20 μR / h) levels were observed in some areas of asphalt. Moreover, the boundaries between the active and inactive asphalt often coincided with the visible boundaries of the asphalt laid at different time periods, or were separated from each other by curbs and curbs.

    A high level of radiation was noted in Red Square, where at certain points the alarm set at 50 μR / h worked steadily (the device was not removed to avoid unnecessary curiosity of people in uniform.

    Radiation levels on lawns and in parks outside of paths are usually 7-10 μR / h. In some places, a slightly elevated level was found, but most often it was not possible to localize the "hot spot". Since the excess of the average level is observed consecutively in 5-8 second counting intervals, it is unlikely that it has a statistical nature, so I assume the role of cloud-shaped accumulations of radon, which, together with the decay products, move in the wind.

    Knowing the presence of a radiation-disadvantaged zone in Kolomenskoye, I visited him. Unfortunately, it was not possible to penetrate the “miserable” coastal slope (where a friend found a pebble from which Terra signaled in the meter — I laid out the gamma spectrum in one of the articles about radiation), and in the park itself it was not beyond the scope described Anomalies could not be detected. But in a completely unexpected place - in the courtyard of one of the houses near the Kursk station near the radiometer, steadily, in three cycles of measurement in a row, suddenly an adaptive alarm went off, the threshold of which is automatically set two sigma above the average minute level. I managed to localize the source right away, and then I discovered it visually - it was a clock hand, apparently covered by SPD! True, the arrow taken out of the ground turned out to be almost inactive - the entire SPD crumbled and remained in the ground.

    Man-made ... low radiation levels

    Oddly enough, and this happens. Unnaturally low dose rates can be found in cars, buses, trains, elevators ... In general, wherever there is a thick, dense (usually metal) inactive barrier between the ground and us. Approximately in vehicles, there is a twofold decrease in the level of radiation background in comparison with the "street" one. The greatest - threefold - attenuation was seen in double-decker trains on the second floor.

    Very low levels of radiation - on some hauls and escalator tunnels in the metro, where the dose rate often falls below 1 μR / h (at stations the background usually grows due to the abundance of granite). On one of the escalators of the Culture Park, the radiometer completely forgets to count - for 10-15 seconds, the display showed zeros and did not sound a single click.

    However, you need to be careful about these numbers because of the move with rigidity. Metal barriers weaken soft gamma radiation to the greatest extent, which leads to a strong underestimation of the readings in these cases.

    Indoor Radiation

    As a rule, building materials (with the exception of wood, glass and metal) contain trace amounts of uranium and thorium, which leads to the fact that the indoor radiation level is higher than on the street. Measurements showed that the level of radiation inside the houses varies greatly, and can be completely different in different rooms. In this case, local anomalies can be detected.

    So, at my institute the radiation level varies from 8 to 20 μR / h in different rooms and corridors. Moreover, the decay products of thorium-232 predominate on the gamma-ray spectra of the background of “luminous” rooms. On the contrary, at a slightly lower level (17 μR / h), uranium-radium predominates.
    In two identical houses built at the same time, the radiation environment can also differ dramatically. So, in two adjacent “Khrushchev” houses on Leninsky Prospekt in Voronezh: radiation at 30 μR / h is measured in one of one of the walls when measured close to it (in a room 15-25 μR / h), plus there are signs of radon infection : wave-like changes in the readings of the radiometer, their decrease after ventilation. In the other - everywhere stable 10 μR / h plus or minus two sigma.

    Radioactive ... people

    Sometimes you walk along the street or in the subway, and suddenly - the radiometer beeped with all three “alarms” at once. He took it out, turned on the screen - and there are completely unhealthy numbers in a couple of hundred micro-roentgen, if not higher, and the graph has not fit into the screen several times and redrawn to a new scale. Usually you should not look for an ampoule from a flaw detector under your feet - a radiation source walks nearby.

    These are people who have recently been examined using radiopharmaceuticals - PET, scintigraphy, etc., as well as treatment with radioactive iodine. Within a few hours or days after the procedure, they emit rather intense radiation. After radioiodine therapy, patients are pooled in the exposure pool before being allowed to go home.they are kept in the hospital for several days until the radiation level drops to reasonable numbers, at which they can already be released to people. After examinations with radiopharmaceuticals, this is usually not necessary, however, patients are advised to limit close communication with children for some time.

    To everything else (these people are already having a hard time with their diagnoses ...), the fact that these patients are constantly “slowed down” at the entrance to the metro is added - “Yantar” (a radiation monitoring complex, whose sensors are usually installed above the entrance doors to metro lobbies) and they have to prove that they are not carrying a "dirty bomb." Its sensitivity is such that after radioiodine therapy, response is still possible for several weeks.

    The screenshot shows the peak that appeared on the device when the metro train passed such a radioactive person.

    Integral dose per day

    And in conclusion, we will evaluate what dose per day we will receive from Moscow radiation and how much it fits into the standards.

    To do this, I again used the integrated dose displayed on the radiometer screen, and for two days I carried the device constantly in my pocket or put it next to me. The following values ​​were obtained:

    1.970 μSv - the dose received in nature (in terms of the day);
    2.873 μSv - the dose per day of the day off, spent entirely in Pushkino, of which 9 hours were at home, 2 hours in the city, the rest - nature (forest, beach).
    3.289 μSv - dose per day of the working day, conducted in the regime of - 9 hours at home, hour (total) on the street of Pushkino, 2 hours (total) in electric train, hour (total) in the metro, the rest - in Moscow (work, rehearsal base, shops, street).

    From technogenic sources (and we will consider everything that comes from building materials, asphalt and other things beyond the natural background, although NRB-99 does not agree with us - but the DNA of our cells does not know what the developers of this document thought) the population is allowed for a year Recruit no more than 1 mSv over the natural background . Multiplying the obtained values ​​by 365 and subtracting the natural background, we get an additional dose in terms of the year:

    • on the day off - 330 μSv / year (with a trip to nature);
    • on the working day - 481 μSv / year.

    As you can see, the additional dose of radiation received in the city, although it did not reach the maximum permissible value in my case, is a significant fraction of it (from a third to half).

    * * *

    Moscow and the Moscow Region are not affected by radiation accidents, there are no significant radioactive contamination (with the exception of the local fruits of the activities of some enterprises and scientific institutions), and there are no nuclear facilities. Nevertheless, the urban environment here is a source of additional radiation in excess of the natural background, which, although not unacceptably large, nevertheless, represents a significant contribution to the total annual dose.

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