IT-65 Geiger counter (radiac meter)

Description: Czechoslovak army Geiger counter.
Manufacturer: Rudi Čajavec and TESLA
Made in year(s): late 60s-mid 80s; 1969 is mine model
Country of origin: Yugoslavia & Czechoslovakia
Status: Working, last calibration Feb 2006

The Intenzimeter IT-65  is an army radioactivity contamination (radiac) intensity metering device used in the former Czechoslovak People’s Army (ČSLA). It is consisting of a Geiger-Müller detector for lower ranges and has an internal ionisation chamber for detecting high contamination levels. The IT-65 was produced as a result of cooperation between former Czechoslovakia and Yugoslavia, since it is a clone of a meter called DR-M3, which was produced in Rudi Čajavec factory in what is now Bosnia. Both devices are almost the same, the “Čajavec” factory logo exists in both versions; just the front panel markings differ, and the Czechoslovak variant IT-65 is equipped with foil capacitors made by TESLA, a former Czechoslovak electrotechnical conglomerate.

IT-65 measurementsMeasuring a small piece of uraninite

The meter itself is made from sturdy plastics, with exception of the faceplate, which is made of metal, and the logarithmic scale is behind a specially-curved glass, which magnifies the numbers a bit, to ease readouts. It has two ranges: 0.05-500 mR/h in Geiger counter mode, and 0.05-500 R/h in ionisation chamber mode. A Western-made Philips 18504 Geiger tube, equipped with a mica window, is present inside the black probe (this probe is permanently attached to the meter) and detects beta, gamma and even alpha radiation, if the probe shield is unscrewed and disassembled. For the second range, the internal ionisaton chamber is used, along with a special electrometric vacuum tube which is sealed inside the chamber. This range is useful only for high level gamma radiation, since the chamber is shielded with a 1mm lead plate to filter out soft rays (this had been removed in my X-ray experiments). In this setting, a manual calibration of the chamber is mandatory, usually done with the KAL pushbutton and knob.

IT-65 probe shield set to beta+gammaBeta and gamma detection, shield open

IT-65 probe set to gamma onlyGamma only detection, shield closed

Accessories included: an instruction manual, 2 weird spare lightbulbs, a 12-24 volt battery eliminator (car adapter) – first versions of this extension have used forementioned lightbulbs instead of resistors to limit the current; an earpiece, a few disposable rubber bags to protect the probe against fallout contamination – these sheats look like condoms 🙂 and a strontium-90 control check source, which was used to check for proper functionality of the meter and for calibration purposes.

Strontium 90 for IT-65Check source

The machine is powered from two 1.5 volt D cells (or from a vehicle through the special cable) and the total weight is 2.8 kg, including the accessories.


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