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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Storozh-R is a device for continuous radiation monitoring. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Dosimeters Technogenic pollution of the environment is often viewed as an inevitable "price" for the conveniences of civilized life that scientific and technological progress provides us with. But if we ourselves can judge pollution, at least somehow manifesting itself, we can somehow minimize their impact on ourselves, then in relation to substances, fields, environments that are inaccessible to our senses, we find ourselves in a different position: not only to take any measures of self-defense, but we cannot simply learn about the appearance of such a danger, even its long-term existence. In such cases, it remains to rely entirely on certain centralized control services, realizing that, by the very nature of their activities, by their physical capabilities, they will at best monitor the average well-being of each of us and its compliance with the standards of their departments. All this fully applies to radiation pollution of the environment - to radioisotopes, to their penetrating radiation: invisible, inaudible, intangible, having neither smell nor taste, even in absolutely unacceptable doses. True, departmental services have recently lost their monopoly right to radiation monitoring in our country - the population has received personal dosimeters. But the "measurement of danger" - this fundamental principle of departmental control, which came to us together with personal dosimeters (mostly simplified models of professional ones), - only at first glance seems to be something that completely replaces organoleptic control. In the fact that none of the human senses can be classified as measuring, one can, of course, see only features of the evolution of living things that do not oblige us to anything. But the fact that the loss of any of them is not compensated by even the most perfect work of modern electronic technology makes us treat the organoleptic orientation - its very ideology, its scale of values - with due attention. As, accordingly, to devices capable of similarly orienting a person in new environments potentially dangerous for him. The technique of personal orientation of a person in the products and waste of modern civilization is designed to solve problems beyond the strength of professional specialists, regardless of their number, qualifications and equipment. Always - as it invariably turned out - insufficient. But what can be the functions of devices for "organoleptic" monitoring of the radiation situation? How, in fact, should they differ from conventional dosimeters? And in general - do we have sufficient funds for this? An organoleptic radiation monitoring device - a radiation technoreceptor - differs from a dosimetric device primarily in its purpose: it is obliged to inform its owner in a timely manner about its proximity to a radiation source, about the appearance of a still potential danger for it. The technical support of this mode of operation of the device affects almost all of its parameters. So, if the energy efficiency of a dosimeter is a rather secondary indicator for it, then for a technoreceptor it is one of the most important: a device that is not able to work continuously, requiring constant care for its energy supply, cannot be attributed to this category at all. On the other hand, the question of the accuracy of the technoreceptor almost loses its meaning. In any case, in the choice between the ability to "see" a wide spectrum of radiation and the accuracy of a quantitative assessment of only some of its varieties - only gamma radiation, for example - the spectral broadband of the device will have unconditional priority. These devices also differ in the form of information presentation. The radiation technoreceptor must include it in the human receptor space. That is, it must be able to inform its owner about the radiation situation and its changes without any request from him. The scoreboards and scales common in measuring technology obviously cannot help here.
Special requirements are also imposed on the reliability of the technoreceptor. It should not only be high, but also constantly checked - the failure of the device should be detected immediately. An organoleptic radiation control device must also have high radiation sensitivity, in any case, be able to control the natural radiation background and almost instantly respond to any noticeable changes in it. And, finally, all this would not be worth much if it were expensive ... In view of the foregoing, "Storozh-R" was designed - a radiation watchman - a device for continuous radiation monitoring. The main parameters
The schematic diagram of the device is shown in fig. 68. Geiger counter type SBM1* is used as an ionizing radiation sensor BD20. High, the voltage at its anode forms a blocking generator: voltage pulses from the step-up winding I of the transformer T1 through the diodes VD1, VD2 charge the filter capacitor C1. The load of the counter is the resistor R1 and the elements associated with the input 8 of the DD1 chip. On the elements DD1.1, DD1.2, C3 and R4, a single vibrator is assembled that converts the pulse coming from the Geiger counter and having a prolonged decline into a "rectangular" one with a duration of 5 ... 7 ms. A fragment of the circuit, which includes elements DD1.3, DD1.4, C4 and R5, is a sound generator controlled by input 6 DD1, excited at a frequency F@1/2·R5·C4@1 kHz, to the paraphase output of which (outputs 3 and 4 DD1) is connected piezo emitter HA1. An acoustic pulse-click is excited in it by a "package" of electrical impulses. On the elements VD4, R8 ... R10, C8 and C9, an integrator is assembled that controls the operation of a threshold amplifier made on a DD2 chip.
The voltage across the capacitor C9 depends on the average excitation frequency of the Geiger counter; when it reaches the unlocking potential of the field-effect transistor included in DD2, the HL1 LED turns on: the frequency and duration of its flashes will increase with increasing radiation levels. The device is mounted on a printed circuit board made of double-sided fiberglass 1,5 mm thick (Fig. 69, a). The foil of the reverse side is used only as a zero bus (it is connected to the "-" power source), in places where the conductors pass, circles with a diameter of 1,5 ... 2 mm are etched in it. The double-ended counter SBM20 is mounted on the printed circuit board with rigid brackets (steel wire with a diameter of 0,8 ... 0,9 mm). They are put on tight on the meter leads and soldered into the holes intended for them. A meter with soft leads (another design of the SBM20 meter) is attached to the body with thin brackets covering it (mounting wire with a diameter of 0,4 ... 0,6 mm), the holes for their soldering are "a-b" and "c-d". Transformer T1 is wound on an M3000NM ring core of size K16x10x4,5 mm. The sharp ribs of the core are pre-smoothed with sandpaper and the entire core is covered with electrically and mechanically strong insulation, for example, they are wrapped with lavsan or fluoroplastic tape. Winding I is wound first, it contains 420 turns of wire PEV-2-0,07. The winding is led almost turn to turn, in one direction, leaving a gap of 1 ... 2 mm between its beginning and end. Winding I is also covered with insulation. Next, winding II-8 turns of wire with a diameter of 0,15 ... 0,2 mm is wound in arbitrary insulation, and on top of it - winding III - 3 turns with the same wire. These windings should also be distributed over the core as evenly as possible. The location of the windings and their terminals must correspond to the printed circuit board drawing, and their phasing must be indicated on the circuit diagram (the common-mode ends of the windings are indicated by dots). It is recommended to cover the finished transformer with a layer of waterproofing - wrap, for example, with a narrow strip of sticky plastic tape. The transformer is fixed to the board with an MXNUMX screw between two elastic washers that do not push through the windings. When assembling the device, it is recommended to use the following types of capacitors: C1 - K73-9-630V, C2 - KD-26-500V, C8 and C9 - K10-17-26, C5 - K53-30 or K53-19; C7, C10 - K50-40 or K50-35. With possible replacements, it should be borne in mind that excessive leakage of capacitors C1 and C2 (as well as the reverse current of diodes VD1 and VD2) can dramatically increase the power consumption of the device. It can be markedly increased by an unfortunate choice of capacitor C5. Resistors: R1 - KIM-0,125 or C3-14-0,125, the rest - MLT-0,125, S2-23-OD25 or S2-33-OD25. As DD1, you can, of course, take the K561LA7 chip. Diode KD510A - replace with any silicon with a pulse current of at least 0,5 A. Almost any LED is suitable, the criterion here is sufficient brightness. The drum-type piezo emitter ZP-1 can be replaced by an emitter with an acoustic resonator - ZP-12 or ZP-22. It is possible to use other piezo emitters. The criterion here is sufficient volume. A fully assembled printed circuit board, a piezo emitter and a switch are installed on the front panel of the device, which is made of high-impact polystyrene 2,5 mm thick (Fig. 69, b). The case of the device, having the shape of an open box, is made of polystyrene 1,5 ... 2 mm thick; along the edge, on its inner side, a groove 2,5 mm deep is selected to fix the front panel of the device in it along its entire perimeter. The cover is fastened to the front panel with an M2 screw, the attachment point is a tide on the power compartment with a metal insert pressed into it, having a thread for the M2 screw. Since the power source in the device is changed very rarely, the sliding cover at the power compartment can be omitted. Since polystyrene can significantly attenuate ionizing radiation (see Appendices 6 and 7), a through cut is made in the case wall adjacent to the Geiger counter, which can only be covered with a rare grating. The same grilles cover the acoustic cutouts in the front panel and in the lid of the device. In "Watchman-R" you can use not only Geiger counters of the SBM20 type. Suitable, without noticeable changes in consumer properties and any alterations of the device, counters such as STS5, SBM32 and SBM32K. But there are Geiger counters that can significantly increase the overall and spectral sensitivity of the device. For example, SBT7, SBT9, SBT10A, SBT11, SI8B, SI13B, SI14B. All of them have thin mica "windows" and are highly sensitive not only to gamma and hard beta radiation, but also to soft beta radiation (and SBT11 also to alpha radiation). True, their configuration will require significant changes in the design of the instrument case, in its overall layout. Some of them will also require an alarm threshold adjustment. Information on domestic-made Geiger counters that can be used in home-made radiation monitoring devices is given in Appendix 4. Nothing, except for the growing dimensions and cost, can interfere with the installation of several Geiger counters in the Storozh-R (they are connected in parallel) - to increase the overall and spectral sensitivity of the device. The device does not require adjustment - correctly assembled, it starts working immediately. But there are two resistors in it, the values \u5b\u8bof which may need to be clarified. This is resistor R8, with the help of which the frequency of the sound generator is brought to the frequency of the mechanical resonance of the piezoelectric emitter (their significant discrepancy affects the volume of the click). And resistor R20, which determines the alarm threshold (the threshold rises with increasing resistance RXNUMX). Threshold correction may be required not only when using a counter that differs significantly from the SBMXNUMX in radiation sensitivity, but also when reconfiguring the device for operation in conditions of an increased background radiation, in conditions, for example, of already existing radiation contamination of the area. "Storozh-R" is easy to use and does not require any special training from the owner. A rare click of acoustic pulses following one after another without any visible order, the absence of an alarm signal (LED flashes) indicate that the device is in a natural radiation background. This background clicking is almost independent of the time of day; season and location of the device, slowing down somewhat only deep underground and accelerating in the highlands. An increase in the count rate when the device is moved, and even more so the appearance of an alarm, with a very high probability means that the device enters the field of an artificial radiation source. The reflex desire of a person to leave this place is a completely appropriate reaction here (moving away from the source is the best form of radiation protection, removing the source is the best decontamination). But you can do this a little later, having previously established the location of the source, its connection with one or another visible object. Since the Storozh-R has maximum sensitivity from its "window" - a cutout in the body wall adjacent to the Geiger counter, this procedure is reminiscent of radio direction finding. The direction to the source can also be determined by approaching it: the source is located in the direction in which the count rate increases as quickly as possible. When searching for sources that are much smaller than the Geiger counter itself, it is recommended to scan suspicious places: move the device, changing its direction of movement and orientation. Thus, the position of a "hot" Particle invisible to the naked eye, for example, is determined with an accuracy of 2...3 mm. However, all this may seem insufficient. It would be desirable to know - it is dangerously found out or not. Let's be clear: this question is not answered, cannot be answered, and probably never will be able to do this with dosimetric instruments of any type. The recipe for separating "dangerous" from "safe" in any complicated cases - and the relationship of living things with radioisotopes of pollution are among the most difficult - may not be at all, in any case - a simple recipe, the implementation of which could be entrusted to the device. But even this is if "safe" radiation exists at least in principle. Unfortunately, in many years of searching, she was never found. It was possible to speak only about its greater or lesser harm. And in civilized countries, the idea of the existence of subthreshold radiation - radiation, the impact of which would be completely compensated by some kind of protective mechanisms of the body - was abandoned. They refused a long time ago, in the USA, for example, in 1946. Minimization of human exposure is an ethical standard in dealing with sources of ionizing radiation. Various departmental standards that accept as acceptable levels significantly exceeding the natural radiation background should be treated as attempts to find a balance, weighing on the universal scales of the business executive the cost of protective measures - on the one hand - and the loss of society from radiation damage - on the other. "Storozh-R" differs from most of the now numerous varieties of household dosimetric devices primarily in that it almost completely eliminates the risk of accidental exposure of its owner. Working in a continuous mode, almost without interfering with other activities (any background, as a sign of a stable situation, easily "leaves" a person's subconscious), he instantly draws his attention to any noticeable change in the radiation situation (another, equally fundamental feature of our perception environment). Storozh-R is especially effective in detecting compact radiation formations - the initial phase of almost any radiation pollution. Unfortunately, in this phase of their existence (the most accessible, by the way, for decontamination), they fall into the field of view of radiation monitoring services only as an exception: even the most advanced, but remote equipment is physically unable to detect such sources. The alarm threshold in the device is set so that it would be under the natural radiation background with almost all possible deviations from the average value. Only very few reasons, not related to artificial radiation sources, can put the "Storozh-R" into alarm mode **. But "Storozh-R" can also be useful in conditions of radiation contamination of the area that has already taken place. The identification of point sources and highly active "spots" against a new, technogenic background may turn out to be even more urgent: experience shows that radiation pollution in such places is extremely uneven. "Storozh-R" - in many of its prototypes and modifications has been tested and used in various regions of our country and abroad over the past forty years. With its help, discarded "luminous" elements of old devices and radioactive ampoules of fire detectors, "hot" particles of Chernobyl on household items and radioactive formations already circulating in the human bloodstream, highly active minerals and fossils in museums and collections, and food products that have passed the triple ( as stated) state control, accelerators of scientific research institutes "illuminating" passers-by and radioactive "dirt" in medical institutions. And many many others... But much more often "Storozh-R" removed unfounded fears and suspicions - what is called radiophobia with a degree of disdain, but in fact is a normal human reaction to an impersonal, "statistically average" attitude towards him. Or, what is the same, SBM-20. In the factory marking, a hyphen is often absent (this also applies to counters of other types). *) The average value of the natural radiation background at sea level is close to 15 μR/h. At a height of 1 km, the background grows approximately twice, at a height of 10...12 km - 10...15 times. There are several places on the globe with abnormally high levels of natural background radiation. It is overestimated by 2...4 times in some areas of France, Brazil, India, Egypt, and by almost 10 times - on the island of Niue in the Pacific Ocean. The reason for such anomalies is the peculiarities of local geological structures, their radionuclide composition.Publication: cxem.net
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