Abstract <p>Fifty years ago, the Unified Track Theory by American professor Robert Katz was very popular all over the world. It was based on the many-hit model of the detector response and the adequacy of the dose-effect relationship. In 1979 we constructed the Refined Unified Track Theory based on the many-hit response model and the differential flux density function of the multiple scattering theory of electrons. According to R. Katz’s theory, the most sensitive detector is the nuclear photoemulsion. From our theory it follows that the most sensitive microvolumes are in glass. This looks like a paradox of sensitivity. The article shows that this is an imaginary paradox.</p>