Indicator of ionizing radiation on microcircuits. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Indicator of ionizing radiation on microcircuits. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

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This indicator reacts to the total flow of ionizing gamma, beta and alpha radiation and, despite its extreme simplicity, is quite reliable in operation.

The indicator circuit consists of a voltage converter and a measurement unit. The voltage converter is assembled according to the key circuit, switching the inductance L1 in the DC circuit with rectification and filtering of the emerging EMF of self-induction.

(click to enlarge)

The master oscillator with a frequency of about 700 Hz is assembled on the elements DD1.1, DD1.2. Since the generated pulses are not symmetrical, a shorter negative half-wave of the pulse is used after inversion to improve efficiency. The voltage rectified by the VD1 diode and filtered by the capacitor C2 (about 380 V) is fed through a load resistor to the Geiger-Muller ionizing radiation counter VL1. It should be noted that the change in the output voltage of the converter, caused by the instability of the power supply, has little effect on the measurement accuracy. In this case, for a STS-5 meter, the input voltage change can be about 90 V.

Short positive pulses arising on the resistor R3 are fed through the buffer inverter DD1.4 to the emitter follower VT2. Capacitor C3 serves to suppress interference from the voltage converter generator. The load of the repeater is the dynamic head BA1 and the LED HL1. The amplitude of the current pulse through the LED and the head is determined by the internal resistance of the power source and the resistance of the collector-emitter of the transistor VT2. And since the control pulses from the element are very short, the average current consumed by the device with a natural background is determined only by the current consumed by the voltage converter.

With an increase in the radiation level to 0,1 mR / h (and, accordingly, an increase in the frequency of the pulses), the average current consumption increases, therefore, for greater efficiency, the dynamic head can be turned off with the SB1 switch.

The site for measuring the level of radioactivity is the simplest analog frequency meter, assembled on the elements DD2.1, DD2.2. The RA1 microammeter serves as an indicator. The node circuit includes a standby multivibrator controlled by pulses from a DD1.4 inverter. The measurement accuracy is ensured by the power supply of the circuit from the VD3R11 parametric stabilizer. The SB2 button is used to switch the microammeter to control the supply voltage through a quenching resistor R10. The measurement limits are switched by the SA1.2 switch by switching the time-setting resistors R6-R8.

The indicator can be assembled with or without a measuring circuit. In the latter case, elements DD2.1, DD2.2, PA1 are excluded. If you use small-sized parts, and leave only the LED to determine the level of radioactivity, then the dimensions of the indicator will not exceed the dimensions of two Krona batteries. The VL1 counter can be replaced by SBM-10, SBM-20, SBM-21, STS, etc. Transistor VT1 - on KT605, transistor VT2 - on any low-power silicon of the corresponding structure. Measuring head PA1 type M4205 with a total deviation current of 100 μA (but it can be any other with a total deviation current of not more than 300 μA). Coil L1 is wound on two ferrite rings M2000NM of size K20x12x6 folded together and contains 200 turns of PELSHO wire 0,26 mm, inductance about 240 mH.

Setting up the indicator is easy. First of all, you need to assemble the input voltmeter divider to measure high voltage. Since the output current of the voltage converter is very small, the voltmeter used must have an input resistance of at least 10 MΩ.

By connecting the divider to capacitor C2, by changing the resistance of resistor R1, set the output voltage to about 380 ... 400 V. If the device is used as an indicator, then the setting ends there.

When using the indicator as a measuring device, it is necessary to calibrate the pointer head. In this case, it can be assumed that the dependence of the number of pulses at the output of the Geiger-Muller counter on the level of radioactivity is linear. If you accurately select the resistance of the timing resistors R6-R8, then you can calibrate the indicator only at one point on the scale. It is done like this. By placing the indicator next to the sensor of the exemplary factory instrument, determine the background level in the area. Let's say it is 0,003 mR / hour. By changing the resistance of the tuning resistor R8, set the arrow PA1 to the "30" division (with a scale of -100 μA). This completes the calibration. Here, however, one circumstance must be taken into account. Due to the counter having its own background, the latter can introduce an error during calibration in the range of 0...0,1 mR/h. Therefore, if possible, it is better to calibrate at elevated background levels, but even in the first case, the accuracy of the meter indicator will be sufficient for practical measurements. Turning on the tuning resistor instead of R10, while pressing the SB2 button, set the microammeter needle to the value corresponding to the supply voltage, and replace the resistor with a constant one. This is where the adjustment ends.

Publication: N. Bolshakov, rf.atnn.ru

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