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Alternatively, the detecting unit can be fastened to the surface where it will be directly
installed is shown in Figure 1 (b). The Figure 1 (b) shows that the barrel of the detecting unit with a
reference point (5), indicating the direction towards the radioactive source, is attached with its base
(2) to the surface using a plank (3). The connecting cable is connected to the connector (4).
1.4.2 Operation principle of the detecting unit
The detecting unit consists of a microcontroller, a high sensitivity detector, a low sensitivity
detector, a supply voltage former, a temperature detector and an RS-485 interface node.
Operation of the detecting unit is based on the method of gamma radiation transformation into
voltage pulse sequence at the detectors' outlet. The high sensitivity scintillation detecting unit
(SDUGR) based on a CsI(Tl) scintillator with 9 cm
200 cps per 1 μSv/h coupled with a semiconductor photomultiplier and a low-sensitive Geiger-
Mueller counter (GMC) of СБМ-21 type are used as detectors in the detecting unit.
The microcontroller processes the pulse flow from the detectors, and forms gamma radiation
DER value, which corresponds to the flow. The microcontroller also calculates a maximum value
of DER measurement statistical error for each gamma radiation DER value. At the same time the
microcontroller runs the power supply of the detectors and continuously controls their operability.
If requested by the data display system, the microcontroller sends a protocol frame via RS-485
interface nod. The protocol frame contains information about current gamma radiation DER,
maximum statistical error in its measurement, and results of the operability control of the detectors.
The supply voltage former transforms voltage from the external power supply to 3.3 V
voltage for powering secondary part of the detecting unit circuit as well as to 350 V for powering
the low sensitivity detector and to 27 V – for the high sensitivity detector.
Figure 1 (b)
3
volume and sensitivity for
6
137
Cs not less than
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