Expressions for the counting rate of rectangular telescopes in the case of single as well as multiple particles are given. The aperture for single particles is obtained in the form of a double integral and analytical solutions are given for some cases. The intensity for different multiplicities of parallel particles is related to the geometry of the detectors and to the features of the radiation. This allows an absolute comparison between the data recorded by different devices.
D'Ettorre Piazzoli, B; Mannocchi, G;  Melone, S;  Picchi, P; Visentin, R 
- Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica
- Istituto di Fisica dell'Universita, Ancona, Italy
- Comitato Nazionale per l'Energia Nucleare, Frascati (Italy). Laboratori Nazionali di Frascati