I don't have much knowledge of soviet society, that's why. Just their cavalier attitude to nuclear safety.

Though to be fair, America wasn't much better in the 50s. Nor was Britain if you read about the "procedures" surrounding the windscale meltdown. Uranium rods would get stuck and people would just poke it with a stick.

The smoke detector in question was created in 70s.

I know but the Soviets continued their attitude until much later, when the Americans had already 'grown up' in terms of nuclear safety.

back in the 50s "fire" detectors had a block of uranium and a vacuum tube to detect smoke or ionized combustive particles