[en] A scanning automatic device was developed to investigate the β-activity distribution on a tape of the electromagnetic mass separator receiver. As a detector the beta-counter was used, ''scanning'' a target throuth the collimator slit. The system could be used to measure the beta-activity on the 80x400 mm² area. The automatic device operating on-line with the computer is applied to analyze a mass spectrum which appears when separating targets activated by the accelerator. A set of mass spectra of radioactive products was obtained, the apparatus resolution was not worse than 3 mm. The exposition time for each of the single isotope-beam traces was 5 sec, the absolute registration efficiency of beta-particle was about 2%, and the back-ground of the SBT-11 beta-counter was 14 pulses/min. The minimal radioactivity counting by the scanning apparatus was approximately 25 radioactive decays/s