Abstract
The GRAPES-3 extensive air shower (EAS) array started operation with 256 scintillator detectors at Ooty in India. Each detector is viewed by a fast photomultiplier tube (PMT) mounted at a height of 60 cm above the scintillator. However, for further expansion of the array, an alternative readout of the scintillator using wave-length shifting (WLS) fibers is employed. This resulted in improved performance with a larger photon signal and a more uniform response. With the inclusion of a second PMT, the dynamic range for particle detection has been increased to ∼5 × 10 3 particles m −2. We now use plastic scintillators, developed in-house to cut costs. The measurement of the density spectrum, shows a power law dependence with an index γ = 1.57 ± 0.04. Using the zenith angle dependence of the density spectrum, an attenuation length Λ a = 98–106 g cm −2 for the EAS is obtained. These measurements are found to be consistent with the results reported earlier by other groups.
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