X-ray photometer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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X-ray photometer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Dosimeters

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The radiometer, according to the scheme shown in the figure, is designed to measure radioactive radiation (gamma and hard beta rays) up to 0,5 R/h, which corresponds to about 3,6 A/kg in the SI system.

X-ray photometer

At the same time, the device is highly sensitive to the rays of the visible part of the spectrum and to infrared rays. This allows you to use it as a photometer and exposure meter.

A cadmium sulfide photoresistor R6 of the FSK-2 type is used as a radiation detector in the device (two FSK-1a photoresistors connected in parallel or a block of ten FSK-5 photoresistors can be used). A constant stabilized voltage of 100 V is applied to the photoresistor. The photocurrent arising from exposure to radiation is amplified by a factor of 107-108 by a composite transistor T2-T5 (1MM6 microcircuit). The IP1 pointer indicator is included in the collector circuit of the latter, which is an M355-1 microammeter with a total deflection current of 50 μA. Its scale is graduated in units of radiation exposure dose rate - R/h. The given sensitivity is set using a trimmer resistor R5, shunting the microammeter.

The device is powered by a battery of three dry cells connected in series 332. The increased voltage for the photoresistors is generated by the converter on the transistor T1 and diodes D1-D4. Diode D5 and resistor R4 form a parametric rectified voltage stabilizer.

The details of the X-ray photometer are mounted on a fiberglass board 2-2,5 mm thick, which is fixed inside the microammeter case. Instead of fiberglass, you can use getinaks. A slot is made in the body of the microammeter, in which the photoresistor window is located.

The Tpl transformer is made on the Ш6Х8 core (from the output transformer of the transistor receiver). Its windings have the following data: 1-2 - 300 and 2-3 - 500 turns of PEV-2 wire 0,07; 4-5 - 4500 turns of PEV-2 0,05.

When measuring the exposure dose rate of gamma and hard beta radiation, the photoresistor window is tightly closed with a retractable shutter made of getinax or textolite 0,8-1 mm thick. The same damper plays the role of an infrared filter when the device is used to detect and measure the intensity of infrared radiation, and the role of a diaphragm when measuring the intensity of light fluxes.

The device is calibrated for gamma and hard beta radiation using the control preparation Co60 (radioactive cobalt) - on a wooden calibration track (table) or by comparing with the readings of any industrial dosimeter.

The distance between the radiation source and the X-ray meter on the calibration line must be maintained with maximum accuracy, while it must be borne in mind that the radiation power dose is inversely proportional to the square of the distance between the source and the X-ray meter (halving the distance increases the dose by four times). It should also be taken into account that the permissible exposure dose of radiation is 2,8 mR/h. Therefore, when calibrating the X-ray meter, one should not approach the radiation source with the device at unacceptably small distances. If it is necessary to calibrate the radiometer for high doses of radiation power, you can use an additional 50 μA microammeter, which is connected in series with the built-in microammeter of the radiometer using an elongated two-wire wire.

Similarly, the device is calibrated as a photometer, replacing the radioactive preparation with a light source, and the dosimeter with a photoexposure meter (photometer). In this case, it is necessary, of course, to take into account the position of the shutter that closes the window of the photoresistor.

Author: S. Vorobev

See other articles Section Dosimeters.

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