Radiation is everywhere. There is she in Moscow. And I was walking my own home-made scintillation radiometer (there will probably be a detailed publication about it soon) to find out which places are the most radioactive in Moscow, what is the source of this radiation and how bad it all is.
Instruments and Techniques
I carried out basic measurements with a homemade scintillation radiometer codenamed Envi RAD
100. The basis of the radiometer is a detector based on a CsI (Tl) crystal measuring 8x8x50 mm and a SiPM photodiode. The owners of Atom Fast must have seen something familiar in this and they will be right - the detector is from it. The radiometer was calibrated using a Cs-137 model source of known (about 100 kBq) activity, lead “house” to reduce and stabilize the background and the ruler and was confirmed by comparison with a verified dosimeter.
The measurements were carried out in the direct pulse counting mode. In this mode, the scintillation radiometer has a significant course with rigidity. However, there is probably no significant contamination by technogenic radionuclides in Moscow (with the exception of certain local places - Kolomna, Shchukino), and the average energy of gamma-quanta of the natural background is just close to the energy of gamma-quanta of cesium, and the error associated with this - for this is small and amounts to no more than 15%.
When measuring the dose rate on the ground, the radiometer was positioned a meter from the ground surface. In all other cases, I will stipulate 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 arrangement is 4 pulses/min, while the count rate from a natural background is approximately 600 imp/min). In principle, this does not change anything, and the level of cosmic radiation is the same everywhere (except for deep-laid underground stations) and almost does not change with time. If you want, you can add 3.5 μR/h to all my figures.
Radiation in nature
To begin, I decided to measure the natural background, minimally exposed to the city. To do this, I walked around the outskirts of the town of Pushkino - near the river Ucha and the Uchinsk reservoir. For a start, I chose an open place, remote from possible man-made radiation sources (such were the railway embankment and bridge, as well as asphalt roads containing crushed granite), as well as from radiation-shielding objects (forest, river). A noticeable variation in the background dose rate from point to point, as well as its fluctuations (apparently due to the release of radon from the soil), was established; therefore, 25 measurements were made at different points with subsequent averaging. The average value was 6.4 μR/h with variations from point to point in the range of 4.5 to 10 μR/h. A “hot spot” was also found with a dose rate of 15–18 μR/h without any visual signs, possibly associated with the presence of moraine origin at a certain depth of granite boulder.
I considered that I received a representative background value until I entered the forest. And I discovered a curious phenomenon: in the forest
the dose rate is stable and statistically significantly higher than near not in the forest
. And it is the fact of the presence of the forest that matters, not the geochemical characteristics of the soil — the radiation level at the site of the felled forest is also lower. With what it can be connected? I don't know.I can only assume that lead-210 is deposited on the leaves from under the radon daughters and shines from everywhere, or the forest interferes with the blowing of radon and its DPR accumulates on the soil, or there is a mechanism similar to that which causes hard x-rays to appear rain - due to the interaction of secondary cosmic radiation with drops (and in this case - with branches and leaves).
The second curious phenomenon is a clear correlation between the radiation level and the soil moisture. As the soil underfoot turns from dry to wet first and then to viscous nyasha, the dose rate over it sharply, up to two times (3-5 μR/h above nyashi), decreases. Here the nature of the phenomenon is clear - with an increase in the water content, the amount of solid matter with which activity is associated decreases.
Similarly, the level drops when approaching the water. If you go with the device to the waist in the water, moving a few meters away from the coast, it simply “forgets to count” - on the display is 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 the parties in nature on Sunday, dividing the difference in readings before and after a walk outside the city by its duration. The result was equal to 8.21 μR/h.
... and in the city
Radiation levels in Moscow are mostly slightly higher than the values prevailing in the open field. In some places, the excess is quite significant.
Almost all of the identified places with a high background are confined to large masses of granite cladding. The greatest 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), steps at the entrance to the Vorobyovy Gory metro station and the stairs leading to ul. Kosygin, on the stairs leading from the lobby of Yaroslavl Art. Komsomolskaya to the platform Komsomolskaya-Radialnaya, underpass stairs under the Pushkino station. Higher levels found in the underpass from the area of the Kursk railway station on the street. The earthen shaft opposite the exits from the Kurskaya-Koltsevaya and Kurskaya-NPS subways. In this transition, the dose rate exceeds 50 μR/h and the highest levels are again on the stairs.
The reason for such a high activity of the stairs, apparently, in the thickness of the granite steps in comparison with the facing tiles.
The screenshot is a typical picture, if you walk along Komsomolskaya from the underground entrance from the trains of the Yaroslavsky railway station through the turnstiles and the red line.
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 in different periods of time, or separated from each other by curbs and curbs.
A high level of radiation is noted on Red Square, where at certain points the alarm set at 50 μR/h was stably activated (the device was not removed in order to avoid unnecessary curiosity of people in shape.
Radiation levels on lawns and in parks outside the lanes 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 average level is exceeded in 5-8 second counting intervals, it is unlikely that it has a statistical nature, so I assume the role of cloud-like clusters of radon, which move with the decay products in the wind.
Being aware of the presence of a radiation dysfunctional zone in Kolomenskoye, I visited him too.Unfortunately, I was unable to penetrate the “zlachny” coastal slope (where an acquaintance found a pebble, from which “Terra” signaled in the meter - I gamma-spectrum I spread it in one of the articles on radiation), and in the park itself there are no no anomalies were found. But in a completely unexpected place - in the courtyard of one of the houses near the Kursk railway station at the radiometer steadily, in three measurement cycles in a row, suddenly an adaptive alarm system triggered, the threshold of which is automatically set two sigma above the average minute level. The source was able to locate immediately, and then I discovered it visually - it was the clock's hand, apparently covered with SPD! True, the arrow taken out of the ground turned out to be almost inactive - the entire SPD crumbled and remained in the ground.
Technogenically ... reduced levels of radiation
Oddly enough, it 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 earth and us. Approximately in vehicles there is a twofold decrease in the background radiation level in comparison with the “street” one. The greatest - threefold - weakening was noticed in double-decker trains on the second floor.
Very low levels of radiation - on some runs in the subway, where the dose rate often drops below 1 μR/h (at stations, the background usually increases due to the abundance of granite).
However, you need to treat these figures with caution because of the course with rigidity. Metal barriers most weaken the soft gamma radiation, which leads to a strong underestimation in these cases.
As a rule, building materials (with the exception of wood, glass and metal) contain a trace of uranium and thorium, which leads to the fact that the indoor radiation level is higher than on the outside. Measurements have shown that the level of radiation inside houses varies greatly, and it can be completely different in different rooms. At the same time, local anomalies can be detected.
So, in my institute the level of radiation varies from 8 to 20 μR/h in different rooms and corridors. At the same time, the thorium-232 decomposition products dominate the gamma-spectra of the background of the “glowing” rooms. On the contrary, at home at a somewhat lower level (17 μR/h), uranium-radium predominates.
In two identical houses built at the same time, the radiation situation can also differ dramatically. Thus, in two adjacent “Khrushchev” houses along Leninsky Prospekt in Voronezh: radiation from under 30 μR/h is measured in one of the walls when measured close to it (15-25 μR/h in the room), plus signs of radon infection are observed: wavelike changes in radiometer readings, their decrease after airing. In the other - everywhere stable 10 μR/h, plus or minus two sigma.
Radioactive ... people
Sometimes you walk down the street or in the subway and suddenly - the radiometer flashes with all three "alarms" at once. I took it out, turned on the screen - and there are completely unhealthy numbers in a couple of hundred micro-roentgens, if not higher, and the graph has not gotten into the screen several times and redrawn to a new scale. Usually you should not look for the ampoule from the flaw detector under your feet - the source of radiation walks nearby.
These are people who have recently been examined with radiopharmaceuticals - PET, scintigraphy, etc., as well as treatment with radioactive iodine. Within a few hours or days after the procedure, they emit fairly intense radiation. After radioiodine therapy of patients, before letting go home,
they relax in the pool.
They are kept in the hospital for several days until the radiation level drops to reasonable numbers at which they can be released to people. After examinations with radiopharmaceuticals, this is usually not necessary, but patients are advised to limit close contact with children for some time.
Everything else (these people and so difficult for their diagnoses ...) the fact that these patients are constantly “slowed down” at the entrance to the subway is added - “Yantar” works (the radiation monitoring complex, the sensors of which are installed usually above the entrance doors in the metro lobbies) and they have to prove that they are not taking with them. ” dirty bomb. Its sensitivity is such that after radioiodine therapy, triggering is still possible within a few weeks.
The screenshot shows the peak drawn on the device when the subway train passed by such a radioactive person.
Integral Dose Per Day
And in conclusion, we will estimate what dose per day we will receive from Moscow radiation and how far it fits into the standards.
For this, I again used the integral 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 weekend, carried out entirely in Pushkino, of which 9 hours - at home, 2 hours - in the city, the rest - in nature (forest, beach).
3.289 μSv - the dose per day of the working day, spent in the mode - 9 hours at home, hour (total) on the street of Pushkino, 2 hours (total) on the train, hour (total) on the subway, the rest - in Moscow (work, rehearsal base, shops, street).
From technogenic sources (and we will be everything that goes beyond the natural background from building materials, asphalt and other things as such, although NRB-99 disagrees with us - but the DNA of our cells does not know what the developers of this document thought there) for a year type no more than 1 mSv over natural background
. Multiplying the values obtained by 365 and subtracting the natural background, we get an additional dose in terms of a year:
- on weekends - 330 µSv/year (with a hike in nature);
- for the working day - 481 µSv/year.
As can be seen, the additional dose of radiation received in the city, although in my case did not reach the maximum permissible value, but makes up a significant proportion of it (from a third to a half).
* * *
Moscow and the Moscow region do not belong to the affected areas of radiation accidents, there are no significant radioactive contamination (with the exception of the local fruits of activity of some enterprises and scientific institutions), there are no nuclear facilities. However, the urban environment here is a source of additional exposure beyond the natural background, which, although not unacceptably large, nevertheless represents a significant contribution to the total annual dose.