Described in the article the indicator was developed in 1986, after Chernobyl. It is made from readily available inexpensive parts. The author's purpose was to create a small, simple, but quite sensitive indicator of environment pollution and food. The description of this indicator was previously published in the magazine "Radio" with significant editorial errors, to fix that editors refused. Below is the author's version of the description of the indicator of radioactivity.
It is known that a person is exposed to both cosmic radiation and terrestrial radiation from radioactive minerals in the soil, building materials, watches and instruments with luminous hands and dials, especially the early editions, which used radium, and radiation from the gas radon, constantly released from the earth's crust. In addition, the radiation sources are currently in use, for example, the smoke sensors. In detail this problem is described in [1].
Notice that a slight excess of background radiation almost safe for a person under external influence. However when getting radioactive material inside, the picture changes dramatically. Particularly harmful alpha particles emitted by such a substance, trapped, for example, the lungs through the dust or in the gastro-intestinal tract with food. They actively destroy surrounding tissue.
To record the presence of radiation using simple indicators is usually required and a stopwatch. To count impulses and simultaneously to follow the arrow of the stopwatch uncomfortable in this indicator, these functions are combined.
Scheme indicator is shown on Fig.1.
Figure. 1
The indicator consists of a high voltage source, a Geiger counter, pulse counter, pulse extender, timer and indicators account on the LEDs.
В качестве счётчика Гейгера BD1 применён СБТ-11, поскольку из всех малогабаритных, имевшихся в то время, только он, благодаря наличию в окне тонкой слюды (20…25 мкм), способен регистрировать частицы с малой энергией.
The high voltage source to power the Geiger counters are assembled by well-known scheme, the blocking-oscillator on the VT1 transistor, pulse transformer T1 and the rectifier with voltage doubler on the elements VD2, VD3, C2, Sz.
With the passage of the particles or gamma-radiation via Geiger counter pulses cause pulsed voltage drop across the resistor R5, which is supplied to the input of the counter of impulses (a conclusion of 2 DD1) and in parallel through the diode VD5 to the extender pulse at the field VT2 transistor КП303А, triggering the flash led HL1. The VD4 diode limits the maximum amplitude of the pulses at the output of the Geiger counter.
On the chip DD1 К176ИЕ5 implemented two node: timer and pulse counter.
After the power is switched on, the counters are set to the zero state by filing a charging current of C7 to the reset input 3 DD 1. Then starts counting of pulses from the Geiger counter with input 2 and pulse generator assembled on the elements C8, C9, R8, R10, part of the micro circuitry with the input 9. The resistor R11 serves for the full discharge of the capacitor C5 before the account.
После заполнения старшего разряда счётчика импульсов со счётчика Гейгера (выводы 2 и 5), загорается HL3, а после заполнения старшего разряда счётчика импульсов генератора (выводы 9,11,12) загорается HL2. Частоту генератора подбирают с помощью R8 такой, чтобы при наличии только фонового излучения HL2 загорался раньше HL3, сигнализируя об отсутствии превышения естественного фона. Если за этот же период времени (примерно 2,5 мин) загорится HL3 – это будет означать, что число частиц превышает фоновое, причем, чем меньше будет промежуток времени между включением индикатора переключателем S1 и загоранием HL3, значит, тем интенсивнее излучение. При большой
the radiation intensity HL3 flashing, and the flashing frequency is proportional to the intensity (as the meter fills faster), and then lights up continuously. Thus, it is possible to estimate radioactive contamination of the environment or products. So, in 1986-1987 I was found a small contamination of some samples of tea, dry herbal and condensed milk.
The indicator is assembled in a metal housing dimensions mm 120x40x30 (photo 1), all parts located on a printed circuit Board (photo 2).
Photo 1
Photo 2
The meter is inserted in the usual semesterly panel and is covered by a hinged protective cover. The switch and LEDs located at the side. The indicator is powered from the battery size "Krona", located inside the housing of the indicator. A pulse transformer was wipan of faulty equipment, the marking has no data is not preserved over years, but you can use any transformer, the production of which is described in detail in [2-4]. You only need to reduce in 2 times the number of turns of high voltage winding, as described in the indicator applied voltage doubling or refuse the doubling.
На выходе выпрямителя при свежей батарее должно быть 450…460 В.
The phone uses parts of the following types:
- R7 – КИМ-0,125;
- R8 – СП-38а;
- остальные резисторы – МЛТ-0,125;
- С5 – К 50-6;
- S2 and Sz tubular KT-m;
- остальные конденсаторы – КМ5, КМ6;
- VD1 – КД510А;
- VD4, VD 5 – КД522А;
- VT1 – КТ315Г;
- VT2 – КП303А;
- HL1-HL3 – АЛ102, АЛ307.
The LEDs is desirable to use high brightness and colorful. In 1986, I had no such.
In the device instead of the specified types of the electronic components is permissible to use the same types of items from other manufacturers.
Наладка индикатора сводится к установке высокого напряжения 450 В (рабочий диапазон счётчика 320…460 В) путём подбора резисторов R1, R2 и установке частоты генератора с помощью R8. Измерение высокого напряжения необходимо проводить вольтметром с высоким входным сопротивлением, например современным цифровым, а частоту генератора устанавливают так, чтобы HL2 загорался чуть раньше, чем HL3 при отсутствии другого источника излучения, кроме естественного фона. Необходимо учитывать, что фон непостоянен, поэтому настройку частоты генератора придётся производить несколько раз.
Ток, потребляемый индикатором в режиме счёта, 0,8…0,9 мА.
Literature
- Радиация. Дозы, эффекты, риск. – М.: Мир, 1990.
- Виноградов Ю. Питание газоразрядного счётчика // Радио. – 1989. – №2.
- Виноградов Ю. Измеритель интенсивности ионизирующего излучения // Радио. – 1990. – N
- Виноградов Ю. О любительских дозиметрах // Радио. – 1992. – №10.
Author: Henry Zakomorny, Tbilisi
