This is a monster Geiger tube capable of detecting even the slightest increase of radiation from a considerable distance (e.g., several feet).  This is due to its long size and increased cathode area. Because of its greater sensitivity (nearly 4 times as sensitive as the popular SBM-20 Russian tube), it is a favorite of many an experimenter or teacher in demonstrating even normal (background) radioactivity to a classroom. (The SBM-19 GM tube was made by a different Soviet factory than the STS-6, but is practically identical in construction and specifications.) https://www.youtube.com/watch?v=046UjxgSf50 https://www.youtube.com/watch?v=GSKuy2fI2IA