Absolute calibration of the amplitude threshold of the FINUDA external scintillator barrel

Two different experimental methods, based on cosmic rays measurements, have been investigated to calibrate in absolute units the scintillation light detected, near the threshold, at both ends of the long scintillators constituting the External Scintillator Barrel of the FINUDA experiment. rst one is based on the selection of the cosmic rays intercepting also the vertex detectors. The second one takes into account all the cosmic rays detected by the barrel itself. ethods are shown to be able to evaluate with enough precision an absolute value of the threshold for neutron detection efficiency calculations.