Measurements of the atmospheric muon flux using a mobile detector based on plastic scintillators read-out by optical fibers and PMTs

Precise measurements of the muon flux are important for different practical applications, in environmental studies and for the estimation of the water equivalent depths of underground sites. A first configuration of the mobile detector was composed of two 1 m(2) scintillator plates, each viewed by wave length shifters and read out by two PMTs (Photomultiplier Tubes). A more recent configuration of the mobile muon detectors, set up in IFIN-HH, Romania, consists of two 1 m(2) detection layers, each one including four 1x0.25 m(2) large scintillator plates. The light output in each plate is collected by twelve optical fibers and then read out by one PMT. The calibration has been made by comparing the energy deposit spectrum of minimum ionizing particles with the spectra simulated with the GEANT4 code. The device is used to measure the muon flux on different locations at the surface and underground.