Microroentgenometer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electronics in medicine
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The microroentgenometer provides measurement of the dose rate of gamma radiation in open areas, in industrial premises, X-ray rooms and laboratories up to 500 μR/s.
The schematic diagram of the device is shown in fig. 1. Under the influence of gamma radiation in the IR ionization chamber, the air is ionized and the voltage applied to its electrodes causes an ordered movement of ions, as a result of which a current of the order of 10-12 ... 10-9 A appears through the chamber. This current passes through the resistor R1 and creates a voltage drop on it proportional to the radiation power. This voltage is applied to the grid of the L1 electrometric triode operating in the cathode follower. The load of the latter is the voltage divider R3-R6.
Rice. 1 (click to enlarge)
Depending on the expected dose rate, switch B1 sets the measurement limit to 5, 50, or 500 μR/s.
On transistors T1 and T2, a DC voltmeter is assembled according to a balanced circuit with an IP1 microammeter for a total deviation current of 50 μA. Resistor R11 serves to calibrate the instrument scale.
The voltage converter on the transistor T3 gives an anode voltage of 6-20 V to the electrometric triode and a voltage of 140-150 V to the ionization chamber. The latter is stabilized by a gas-filled zener diode L2, the anode voltage of the lamp L1 by silicon zener diodes D3 and D4. The required value of this voltage is set using the potentiometer R16. The operating mode of the blocking generator of the voltage converter is set by a variable resistor R20.
The incandescence of the L1 triode is powered by element 373 or one element from a 3336L pocket flashlight battery. The filament voltage of this lamp is set in the range of 0,5-0,7 V using a variable wire resistor R2. The voltage converter and transistor voltmeter are powered by battery B2 (3336L). The voltmeter meter is set to zero by adjusting the variable resistor R10, while the Kn1 button closes the resistor R1.
The microroentgenometer is mounted in a housing measuring 210x100x125 mm. The ionization chamber is built into the same housing.
The transformer Tp1 of the blocking generator is made on the magnetic circuit Ш6х12. Winding data: 1-2 - 300 turns of PEV-2 0,1; 2-3 - 500 turns of PEV-2 0,08; 4-5 - 800 turns of PEV-2 0,1: 5-6 - 3200 turns of PEV-2 0,05; 6-7 - 1000 turns of PEV-2 0,05.
Author: S. Vorobev
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