Radiometer KDG-1
A retro-look to dosimetry equipment

Back to 70s and beginning of 80s, most of devices were analog-based, and displayed power of the dose using microampermeter with custom dial. A principle of operation of nearly all of them is based on measurement of average frequency of impulses produced by Geiger tube during registering γ-radiation, that are transmitted to measurement circuit board, that counts them and charge the main capacitor accordingly. This charge then displayed on a meter.

Soviet dosimeter

This particular device is KDG-1 (КДГ-1). Originally designed for marine use and for dosimetry control of cargo, it is one of quite small number of radiometers that could measure levels of γ-radiation up to an astronomical number — 1000 Roentgens per hour (approximately 10 Sv/h). Due to good selection of detection block material, it reacts faster than DP-5V, which is quite crucial when measurements being done in heavy radiation fields. So, despite of their initial purpose, such devices, along with beta-counters KRB-1 got their application during initial phase of Chernobyl disaster liquidation.

Let's take a closer look.

Soviet dosimeter

Soviet dosimeter

KDG-1 consists of portable measuring block and precisely-finished telescopic handle. On the end of the handle there is a detection block, based on a Geiger tube with rotary cover. If the cover is open, device will register β-particles if some strong flow (more than 600 decays / cm * min) is present.

The measuring block itself is solid-built, with compartment for 3 x R12 batteries. A meter installed, is equipped with light-charging glowing dial, so it glows pretty bright, making measurements easier in dark time. Additionally it is mounted in a thick plastic box, that provides protection from humidity and vibration.

Soviet dosimeter

The main control is rotary knob, that allows to change a mode of operation — switching on, testing batteries, setting up zero, and make meaurements with different scales — х1 mR/h, х10 mR/h, х100 mR/h, x1 R/h, x10 R/h and x100 R/h.

Soviet dosimeter

The common problem of analog devices of that times was even not that much their accuracy (this one has, for example, 30% mistake probability), like the fact that are quite slow. In case of severe radiation level it increases the risk for operator to get unwanted personal dose. For example, In case of this device, a user manual requires one-minute warm-up and setting up zero (using small rotary knob on the right top of device). Given that display functions based on capacitor's charge, in case of significant changes of radiation flow, an analog device can 'freeze' for a while. To eliminate this effect, KDG-1 equipped with reset function triggered by a button under the meter.

In conclusion, in the condition of modern Zone this is more a historical artifact — on the routes permitted for visitors it won't react very much even on the lowest scale set up — as minimal level it capable to register is 100 µR/h (approximately 1 µSv/h). However, it is a perfect device to understand and feel, what a work of dosimetrist on that hard times looked like.

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