Abstract: The present invention relates to a process for the detection of superimposed sheets, the apparatus making it possible to perform this process and the application thereof to bank notes. The process for detecting superimposed sheets by evaluating their surface mass is characterized in that it comprises the stages of passing the sheets oriented in the direction of their width between a beta particle source and a Geiger-Muller counter, counting the number of particles received by the counter by measuring the frequency F.sub.g of the pulses from the Geiger counter to determine the surface mass and eliminating the notes having a high superimposition level by comparison with a limit value.

Abstract: Apparatus for separating and extracting stacked sheets one by one, in which the top sheet is driven by a friction roller only forward in the extraction direction and is passed between two rollers 6, 9 which have suitable profiles to curve it transversely at least once. Roller 6 rotates with the friction roller, while roller 9 is permitted only a few degrees of rotation in the forward direction and is then spring-returned, preferably to slightly beyond its initial position; so that the roller 9 indexes slightly in the counterfeed direction with each dispensing cycle, thereby evenly distributing wear around its periphery.The invention applies in particular to bank-note extractors.